Twin hull variable draft drilling vessel

Abstract

The vessel comprises a pair of laterally spaced elongated hulls having a plurality of upstanding columns spaced therealong supporting a working platform in spaced relation above the hulls a distance slightly greater than the maximum anticipated wave height. The hulls buoyantly support the vessel in a low draft floating condition with the hulls having freeboard. The hulls have ballast compartments to submerge the hulls and portions of the stabilizing columns to a distance of approximately half the effective height of the stabilizing columns which is slightly greater than maximum anticipated wave height, to maintain the vessel in a high draft floating condition with the platform elevated above the waterline. The columns stabilize the vessel in the high draft condition about roll and pitch axes. The working platform mounts either a drilling rig or a heavy duty crane or like operational equipment along the centerline of the vessel. .[.This application is a continuation-in-part of application Ser. No. 666,395, filed Sept. 8, 1967 and now abandoned..]..Iadd.

What is claimed and desired to be secured by United States Letters Patent is: 
     
       1. A variable draft vessel comprising: a pair of elongated hulls disposed in side-by-side spaced substantially parallel relation one to the other;   a working platform;   means connected to said hulls and said platform to support said platform in spaced relation above said hulls;   said connecting means including at least six upstanding stabilizing columns disposed on said hulls, a pair of said columns being located adjacent opposite ends of said hulls on opposite sides of the pitch axis of the vessel, at least three columns being located on each hull and on opposite sides of the roll axis of the vessel;   said hulls having a combined displacement sufficient to float the vessel in a low draft condition with the hulls having freeboard;   and means for ballasting and deballasting the vessel to respectively submerge the hulls and portions of said connecting means below said platform below the waterline thereby to provide a high draft condition and refloat the vessel with the hulls having freeboard, the displacement of the submerged hulls and portions of said connecting means being sufficient to maintain the vessel buoyant in the high draft condition;   said connecting means being spaced one from the other to provide an open frame area between the components thereof and between said platform and said hulls;   the cross sectional area and configuration of said columns, the weight distribution of the vessel, and the geometry of the submerged hulls and portions of said connecting means being such as to maintain the natural period of the vessel in the high draft condition no less than six seconds;   said vessel having a length to width ratio of at least 2 to 1;   said stabilizing columns being connected to said hulls on the outboard sides thereof with the distance between the pitch axis and the centroid of the stabilizing columns on opposite sides of the pitch axis being greater than the transverse distance between the roll axis and the centroid of the stabilizing columns on opposite sides of the roll axis, said stabilizing columns having outboard portions thereof which extend transversely beyond the outboard sides of the respective hulls thereby providing increased moment for stabilizing action about the roll axis.   
     
     
       2. A variable draft vessel comprising: a pair of elongated hulls disposed in side-by-side spaced substantially parallel relation one to the other;   a working platform;   means connected to said hulls and said platform to support said platform in spaced relation above said hulls; said connecting means including at least four stabilizing columns located on said hulls with a pair of said columns on each of the opposite sides of the respective pitch and roll axes of the vessel;   said hulls having a combined displacement sufficient to float the vessel in a low draft condition with the hulls having freeboard;   and means for ballasting and deballasting the vessel to respectively submerge the hulls and portions of said connecting means below said platform below the waterline thereby to provide a high draft condition and refloat the vessel with the hulls having freeboard, the displacement of the submerged hulls and portions of said connecting means being sufficient to maintain the vessel buoyant in the high draft condition;   said connecting means being spaced one from the other to provide an open frame area between the components thereof, and between said hulls and said platform;   the cross sectional area and configuration of the columns, the weight distribution of the vessel, and the geometry of the submerged hulls and portions of said connecting means being such as to maintain the natural period of the vessel in the high draft condition no less than 6 seconds; said stabilizing columns being connected to said hulls on the outboard sides thereof with the distance between the pitch axis and the centroid of the stabilizing columns on opposite sides of the pitch axis being greater than the transverse distance between the roll axis to the centroid of the stabilizing columns on opposite sides of the roll axis, said stabilizing columns having outboard portions thereof which extend transversely beyond the outboard sides of the respective hulls thereby providing increased moment for stabilizing action about the roll axis.   
     
     
       3. A variable draft vessel comprising: a pair of elongated hulls disposed-in side-by-side spaced substantially parallel relation one to the other;   a working platform;   a plurality of elements upstanding from said hulls with at least a portion of said elements being connected to said platform to support the platform in spaced relation above the hulls a predetermined height at least equal to the height of the maximum anticipated wave; at least a portion of said upstanding elements including at least six stabilizing columns disposed on said hulls and upstanding therefrom a predetermined effective height at least equal to the height of the maximum anticipated wave, a pair of said columns being located adjacent opposite ends of said hulls on opposite sides of the pitch axis of the vessel, at least three columns being located on each hull and on opposite sides of the roll axis of the vessel;   said hulls having a combined displacement sufficient to float the vessel in a low draft condition with the hulls having freeboard;   and means for ballasting and deballasting the vessel to respectively submerge the hulls and portions of said elements below the waterline thereby to provide a high draft condition and refloat the vessel with the hulls having freeboard, the displacement of the submerged hulls and portions of said elements being sufficient to maintain the vessel buoyant in the high draft condition;   said elements being spaced one from the other to provide an open frame area therebetween and between said platform and hulls;   the cross sectional area and configuration of the columns, the weight distribution of the vessel and the geometry of the submerged hulls and portions of said elements being such as to maintain the natural period of the vessel in the high draft condition no less than 6 seconds;   said vessel having a length to width ratio of at least 2 and 1;   the displacement of the submerged hulls and portions of said elements being sufficient to maintain the vessel buoyant in the high draft condition with the mean waterline located a distance above the hulls at substantially one-half the effective height of said stabilizing columns;   said stabilizing columns being connected to said hulls on the outboard sides thereof with the distance between the pitch axis and the centroid of the stabilizing columns on opposite sides of the pitch axis being greater than the transverse distance between the roll axis and the centroid of the stabilizing columns on opposite sides of the roll axis, said stabilizing columns having outboard portions thereof which extend transversely beyond the outboard sides of the respective hulls thereby providing increased moment for stabilizing action about the roll axis.   
     
     
       4. A variable draft vessel comprising: no more than two hulls disposed in side-by-side spaced substantially parallel relation one to the other; a working platform;   means connected to said hulls and said platform to support said platform in spaced relation above said hulls a predetermined height at least equal to the height of the maximum anticipated wave, said connecting means including at least six upstanding stabilizing columns disposed on said hulls and upstanding therefrom a predetermined effective height of at least equal to the height of the maximum anticipated wave, a pair of said columns being located adjacent opposite ends of said hulls on opposite sides of the pitch axis of the vessel, at least three columns being located on each hull and on opposite sides of the roll axis of the vessel;   said hulls having a combined displacement sufficient to float the vessel in a low draft condition with the hulls having freeboard;   and means for ballasting and deballasting the vessel to respectively submerge the hulls and portions of the connecting means below said platform below the waterline thereby to provide a high draft condition and refloat the vessel with the hulls having freeboard, the displacement of the submerged hulls and portions of said connecting means being sufficient to maintain the vessel buoyant in the high draft condition;   said connecting means being spaced one from the other to provide an open frame area between the components thereof and between said platform and said hulls;   said vessel having a length to width ratio of at least 2 to 1;   said stabilizing columns being connected to said hulls on the outboard sides thereof with the distance between the pitch axis and the centroid of the stabilizing columns on opposite sides of the pitch axis being greater than the transverse distance between the roll axis and the centroid of the stabilizing columns on opposite sides of the roll axis, said stabilizing columns having outboard portions thereof which extend transversely beyond the outboard sides of the respective hulls thereby providing increased moment for stabilizing action about the roll axis.   
     
     
       5. A variable draft vessel comprising: no more than two hulls disposed in side-by-side spaced substantially parallel relation one to the other;   a working platform;   means connected to said hulls and to said platform to support said platform in spaced relation above said hulls a predetermined height at least equal to the height of the maximum anticipated wave, said connecting means including at last six upstanding stabilizing columns disposed on said hulls and upstanding therefrom a predetermined effective height at least equal to the height of the maximum anticipated wave, a pair of said columns being located adjacent opposite ends of said hulls on opposite sides of the pitch axis of the vessel, at least three columns being located on each hull and on opposite sides of the roll axis of the vessel with the cross sectional area of said columns being substantially constant throughout the effective height thereof;   said hulls having a combined displacement sufficient to float the vessel in a low draft condition with the hulls having freeboard;   and means for ballasting and deballasting the vessel to respectively submerge the hulls and portions of said connecting means below the waterline thereby to provide a high draft condition and refloat the vessel with the hulls having freeboard, the displacement of the submerged hulls and portions of said connecting means being sufficient to maintain the vessel buoyant in the high draft condition with the mean waterline located a distance above the hulls at substantially one-half the effective height of said stabilizing columns;   said connecting means being spaced one from the other to provide an open frame area between the components thereof and between said platform and said hulls;   the cross sectional area and configuration of said columns, the weight distribution of the vessel and the geometry of the submerged hulls and portions of said connecting means being such as to maintain the natural period of the vessel in the high draft condition no less than 6 seconds;   said vessel having a length to width ratio of at least 2 to 1;   said stabilizing columns being connected to said hulls on the outboard sides thereof with the distance between the pitch axis and the centroid of the stabilizing columns on opposite sides of the pitch axis being greater than the transverse distance between the roll axis and the centroid of the stabilizing columns on opposite sides of the roll axis, said stabilizing columns having outboard portions thereof which extend transversely beyond the outboard sides of the respective hulls thereby providing increased moment for stabilizing action about the roll axis.   
     
     
       6. A variable draft vessel comprising: a base structure having hydrostatic and hydrodynamic characteristics;   a working platform;   a plurality of elements upstanding from said base structure with at least a portion of said elements being connected to said platform to support said platform in spaced relation about said base structure, at least a portion of said upstanding elements including at least six stabilizing columns disposed on said base structure with a pair of said columns being located adjacent opposite ends of said base structure on opposite sides of the pitch axis of the vessel, at least three columns being located on said base structure on opposite sides of the roll axis of the vessel;   said base structure having displacement sufficient to float the vessel in a low draft condition with the base structure having freeboard;   and means for ballasting and deballasting the vessel to respectively submerge the base structure and portions of said elements below the waterline thereby to provide a high draft condition and refloat the vessel with the base structure having freeboard;   said elements being spaced one from the other to provide an open frame area therebetween and between said platform and said hulls;   the cross sectional area and configuration of said columns, the weight distribution of the vessel, and the geometry of the submerged base structure and portions of said elements being such as to maintain the natural period of the vessel in the high draft condition no less than 6 seconds;   said vessel having a length to width ratio of at least 2 to 1;   said stabilizing columns being connected to said base structure on the outboard sides thereof with the distance between the pitch axis and the centroid of the stabilizing columns on opposite sides of the pitch axis being greater than the transverse distance between the roll axis and the centroid of the stabilizing columns on opposite sides of the roll axis, said stabilizing columns having outboard portions thereof which extend transversely beyond the outboard sides of the base structure thereby providing increased moment for stabilizing action about the roll axis. .[.7. A variable draft vessel comprising:   a pair of elongated flotation members disposed in side-by-side spaced substantially parallel relation one to the other;   a working platform;   means connected to said flotation members and said platform to support said platform in fixed spaced relation above said members;   said connecting means including at least six upstanding stablizing columns disposed on said members, a pair of said columns being located adjacent opposite ends of said members on opposite sides of the pitch axis of the vessel, at least three columns being located on each member and on opposite sides of the roll axis of the vessel;   said platform being spaced above said members a predetermined height at least equal to the height of the maximum anticipated wave, said columns upstanding from said members a predetermined effective height at least equal to the height of the maximum anticipated wave, the cross sectional area of said columns being substantially constant throughout the effective height thereof;   said members having a combined displacement sufficient to float the vessel in a low draft condition with the members having freeboard;   means for ballasting and deballasting the vessel to respectively submerge the members and portions of said connecting means below said platform below the waterline thereby to provide a high draft, otherwise unsupported, floating condition and return the vessel to the low draft condition with the members having freeboard, the displacement of the submerged members and portions of said connecting means being sufficient to maintain the vessel buoyant in the high draft floating condition;   said connecting means being spaced one from the other to provide an open frame area between the components thereof and between said platform and said members;   the combined water plane areas of said columns forming at least the major portion of the total water plane area of said vessel in the high draft condition;   the cross sectional area and configuration of said columns, the weight distribution of the vessel, and the geometry of the submerged members and portions of said connecting means being such that the vessel obtains motion minimizing characteristics in the high draft condition;   and means carried by the vessel for conducting drilling operations while the vessel is maintained in the high draft floating condition;   said vessel having a length to width ratio of about 2 to 1..]. .[.8. A vessel according to claim 7 wherein the natural periods in pitch and roll of the vessel in the high draft condition lie within a range of 6 to 40 seconds..]. .[.9. A vessel according to claim 7 wherein the displacement of said submerged members and portions of said connecting means is sufficient to maintain the vessel buoyant in the high draft condition with the mean waterline located a distance above said members at substantially one-half the effective height of said stabilizing columns;   said ballasting and deballasting means being operable to vary the submergence of the vessel when in the high draft condition such that the distance between the mean waterline and either the underside of the platform or the topside of said members is not less than 0.75 of the mean wave height for wave heights less than the maximum anticipated wave to preclude amplification of vessel motion due to interaction of wave and vessel motion..]. .[.10. A vessel according to claim 7 including a stabilizing column on each member located adjacent the transverse axis through the center of flotation of the vessel, said connecting means including a plurality of support members forming trusses extending between said member and said platform at spaced longitudinal positions along the vessel, said trusses including transversely extending elements connecting one member to the other with said elements lying above the uppermost portions of said flotation members..]. .[.11. A vessel according to claim 7 wherein at least one of said stabilizing columns on each said member has a cross section elongated in a direction substantially parallel to the roll axis of the vessel..]. .[.12. A vessel according to claim 7 wherein at least one of said stabilizing columns on each said member is substantially oblong in cross section and extends longitudinally parallel to said member a distance greater than its width..]. .[.13. A vessel according to claim 7 wherein said drilling means includes a drilling rig mounted on said platform over the space between said members..]. .[.14. A vessel according to claim 7 wherein each of said members has bow and stern designs to minimize resistance to movement through the water in said low draft condition..]. .[.15. A vessel according to claim 7 wherein the centroids of said columns are transversely spaced from vertical planes containing the longitudinal centerlines of said members..]. .[.16. A vessel according to claim 7 wherein the centroids of said columns are spaced outboard of vertical planes passing through the longitudinal centerlines of said members..]. .[.17. A vessel according to claim 7 including a crane for transferring loads between horizontally spaced positions..]. .[.18. A vessel according to claim 7 wherein said ballasting and deballasting means includes at least two ballast compartments in each of said members, said two ballast compartments being horizontally spaced one from the other, and means for selectively ballasting and deballasting said two compartments in each said member to alter the natural period of said vessel..]. .[.19. A vessel according to claim 18 wherein said ballasting and deballasting means includes at least four ballast compartments in each of said members, a pair of said ballast compartments in each member being transversely spaced one from the other, another pair of said ballast compartments in each member being longitudinally spaced one from the other and means for effecting ballast transfer into and out of the ballast compartments of each said pair thereof to alter the natural period of said vessel about roll and pitch axes..]. .[.20. A variable draft vessel comprising: a pair of elongated hulls disposed in side-by-side spaced substantially parallel relation one to the other;   a working platform;   means connected to said hulls and said platform to support said platform in fixed spaced relation above said hulls;   said connecting means including at least four stabilizing columns located on said hulls with a pair of said columns on each of the opposite sides of the respective pitch and roll axes of the vessel;   the cross sectional area of said columns being substantially constant throughout the height thereof;   said hulls having combined displacement sufficient to float the vessel in a low draft condition with the hulls having freeboard, each of said hulls having bow and stern designs to minimize resistance to movement through the water in said low draft condition;   means for ballasting and deballasting the vessel to respectively submerge the hulls and portions of said connecting means below said platform below the waterline thereby to provide a high draft, otherwise unsupported, floating condition and return the vessel to the low draft condition with the hulls having freeboard, the displacement of the submerged hulls and portions of said connecting means being sufficient to maintain the vessel buoyant in the high draft floating condition;   said connecting means being spaced one from the other to provide an open frame area between the components thereof, and between said hulls and said platform;   the combined water plane areas of said columns forming at least the major portion of the total water plane area of said vessel in the high draft condition;   the cross sectional area and configuration of the columns, the weight distribution of the vessel, and the geometry of the submerged hulls and portions of said connecting means being such that the vessel obtains moton minimizing characteristics in the high draft condition;   and means carried by the vessel for conducting drilling operations while   
     
     
        the vessel is maintained in the high draft floating condition..]. .[.21. A vessel according to claim 20 wherein said connecting means includes at least 6 upstanding stabilizing columns disposed on said hulls, a pair of said columns being located adjacent opposite ends of said hulls on the opposite sides of the pitch axis of the vessel, at least 3 columns being located on each hull and on opposite sides of the roll axis of the vessel..]. .[.22. A vessel according to claim 20 having a length to width ratio of at least 2 to 1..]. .[.23. A vessel according to claim 20 wherein said platform is spaced above said hulls a predetermined height at least equal to the height of the maximum anticipated wave, said columns upstanding from said hulls a predetermined effective height at least equal to the height of the maximum anticipated wave..]. .[.24. A vessel according to claim 20 wherein the natural periods in pitch and roll of the vessel in the high draft condition lies within a range of 6 to 40 seconds..]. .[.25. A vessel according to claim 23 wherein the displacement of said submerged hulls and portions of said connecting means is sufficient to maintain the vessel buoyant in the high draft condition with the mean waterline located a distance above said hulls at substantially one-half the effective height of said stabilizing columns; said ballasting and deballasting means being operable to vary the submergence of the vessel when in the high draft condition such that the distance between the mean waterline and either the underside of the platform or the topside of said hulls is not less than 0.75 of the mean wave height to preclude amplification of vessel motion due to interaction of wave and vessel motion..]. .[.26. A vessel according to claim 20 wherein said drilling means includes a drilling rig mounted on said platform over the space between the hulls..]. .[.27. A vessel according to claim 24 wherein said ballasting and deballasting means include a plurality of compartments in each of said hulls together with means for selectively ballasting and deballasting said compartments..]. .[.28. A vessel according to claim 20 wherein the centroids of said columns are transversely spaced from vertical planes passing through the longitudinal centerlines of said hulls..]. .[.29. A vessel according to claim 20 wherein said platform is spaced above said hulls a predetermined effective height at least equal to the height of the maximum anticipated wave, said columns upstanding from said hulls a predetermined effective height at least equal to the height of the maximum anticipated wave, said ballasting and deballasting means including a plurality of compartments in each of said hulls together with means for selectively ballasting and deballasting said compartments, the displacement of the submerged hulls and portions of said connecting means being sufficient to maintain the vessel buoyant in the high draft condition with the mean waterline located a distance above the hulls at substantially one-half the effective height of said stabilizing columns..]. .[.30. A vessel according to claim 20 wherein said ballasting and deballasting means includes at least two ballast compartments in each of said hulls, said two ballast compartments being horizontally spaced one from the other, and means for selectively ballasting and deballasting said two compartments in each said hull to alter the natural period of said vessel..]. .[.31. A variable draft vessel comprising: a pair of elongated flotation members disposed in side-by-side spaced substantially parallel relation one to the other;   a working platform;   a plurality of elements upstanding from said members with at least a portion of said elements being connected to said platform to support the platform in spaced relation above the members; at least a portion of said upstanding elements including at least six stabilizing columns disposed on said members and upstanding therefrom a predetermined height, a pair of said columns being located adjacent opposite ends of said members on opposite sides of the pitch axis of the vessel, at least three columns being located on each member and on opposite sides of the roll axis of the vessel;   the cross sectional area of said columns being substantially constant throughout the predetermined height thereof;   said flotation members having a combined displacement sufficient to float the vessel in a low draft condition;   means for ballasting and deballasting the vessel to respectively submerge the members and portions of said elements below the waterline thereby to provide a high draft, otherwise unsupported, floating condition and return the vessel to a low draft condition; the displacement of the submerged members and portions of said elements being sufficient to maintain the vessel buoyant in the high draft floating condition;   said elements being spaced one from the other to provide an open frame area therebetween and between said platform and members;   the combined water plane areas of said columns forming at least the major portion of the total water plane area of said vessel in the high draft condition;   the cross sectional area and configuration of the columns, the weight distribution of the vessel and the geometry of the submerged members and portions of said elements being such that the vessel obtains motion minimizing characteristics in the high draft condition;   and means carried by the vessel for conducting drilling operations while the vessel is maintained in the high draft floating condition;   said vessel having a length to width ratio of at least 2 to 1..]. .[.32. A vessel according to claim 31 including a crane for transferrng loads between horizontally spaced positions..]. .[.33. A vessel according to claim 31 wherein the displacement of the submerged members and portions of said elements is sufficient to maintain the vessel buoyant in the high draft condition with the mean waterline located a distance above the members at substantially one-half the predetermined height of said stabilizing columns..]. .[.34. A vessel according to claim 31 wherein the natural periods in pitch and roll of the vessel in the high draft condition lie within a range of 6 to 40 seconds..]. .[.35. A vessel according to claim 33 wherein said columns upstand from said members a predetermined height at least equal to the height of the maximum anticipated wave; said ballasting and deballasting means being operable to vary the submergence of the vessel when in the high draft condition such that the distance between the mean waterline and either the underside of the platform or the topside of said members is not less than 0.75 of the mean wave height for wave heights less than the maximum anticipated wave to preclude amplification of vessel motion due to interaction of wave and vessel motion..]. .[.36. A vessel according to claim 33 including a stabilizing column on each member located adjacent the transverse axis through the center of flotation of the vessel, said connecting means including a plurality of trusses extending between said members and said platform at spaced longitudinal positions along the vessel, said trusses including transversely extending elements connecting one member to the other with said elements lying adjacent the uppermost portions of said members..]. .[.37. A vessel according to claim 31 wherein at least one of said stabilizing columns on each said member has a cross section elongated in a direction substantially parallel to the roll axis of the vessel..]. .[.38. A vessel according to claim 37 wherein the centroid of said one stabilizing column on each said member is spaced outboard of the vertical plane containing the longitudinal centerline of the corresponding member..]. .[.39. A vessel according to claim 31 wherein the members have freeboard in the low draft condition of the vessel..]. .[.40. A vessel according to claim 31 wherein said platform is fixed in spaced relation above said members each of said members having bow and stern designs to minimize resistance to movement through the water in said low draft condition..]. .[.41. A vessel according to claim 31 wherein said ballasting and deballasting means includes at least two ballast compartments in each of said members, said two ballast compartments being horizontally spaced one from the other, and means for selectively ballasting and deballasting said two compartments in each said member to alter the natural period of said vessel..]. .[.42. A variable draft vessel comprising: no more than two hulls disposed in side-by-side spaced substantially parallel relation one to the other;   a working platform;   means connected to said hulls and said platform to support said platform in spaced relation above said hulls, said connecting means including at least six upstanding stabilizing columns disposed on said hulls and upstanding therefrom a predetermined effective height, a pair of said columns being located adjacent opposite ends of said hulls on opposite sides of the pitch axis of the vessel, at least three columns being located on each hull and on opposite sides of the roll axis of the vessel;   said hulls having a combined displacement sufficient to float the vessel in a low draft condition with the hulls having freeboard;   the cross sectional area of said columns being substantially constant throughout the effective height thereof;   means for ballasting and deballasting the vessel to respectively submerge the hulls and portions of the connecting means below said platform below the waterline thereby to provide a high draft, otherwise unsupported, floating condition and return the vessel to the low draft condition with the hulls having freeboard, the displacement of the submerged hulls and portions of said connecting means being sufficient to maintain the vessel buoyant in the high draft floating condition;   said connecting means being spaced one from the other to provide an open frame area between the components thereof and between said platform and said hulls;   the combined water plane areas of said columns forming at least the major portion of the total water plane area of said vessel in the high draft condition;   and means carried by the vessel for conducting drilling operations while the vessel is maintained in the high draft floating condition;   said vessel having a length to width ratio of at least 2 to 1..]. .[.43. A vessel according to claim 42 including a crane for transferring loads between horizontally spaced positions..]. .[.44. A vessel according to claim 42 wherein the displacement of the submerged hulls and portions of said connecting means is sufficient to maintain the vessel in the high draft condition with the mean waterline located a distance above the hulls at substantially one-half the effective height of said stabilizing columns..]. .[.45. A vessel according to claim 42 wherein the cross sectional area and configuration of the columns, the weight distribution of the vessel and the geometry of the submerged hulls and portions of said connecting means are such that the vessel obtains a natural period in the high draft condition no less than 6 seconds..]. .[.46. A vessel according to claim 44 wherein said ballasting and deballasting means is operable to vary the submergence of the vessel when in the high draft condition such that the distance between the mean waterline and either the underside of the platform or the topside of said hulls is not less than 0.75 of the mean wave height for wave heights less than the maximum anticipated wave to preclude amplification of vessel motion due to interaction of wave and vessel motion..]. .[.47. A vessel according to claim 42 wherein said stabilizing columns are substantially oblong in cross section and extend longitudinally parallel to said hulls a distance greater than their width..]. .[.48. A vessel according to claim 42 wherein said drilling means includes a drilling rig mounted on said platform over the space between the hulls..]. .[.49. A vessel according to claim 42 wherein said platform is fixed in spaced relation above said hulls, each of said hulls having bow and stern designs to minimize resistance to movement through the water in said low draft condition..]. .[.50. A vessel according to claim 42 wherein said ballasting and deballasting means includes at least two ballast compartments in each of said hulls, said two ballast compartments being horizontally spaced one from the other, and means for selectively ballasting and deballasting said two compartments in each said hull to alter the natural period of said vessel..]. .[.51. A vessel according to claim 42 wherein the cross sectional area and configuration of said columns, the weight distribution of the vessel and the geometry of the submerged hulls and portions of said connecting means being such as to provide motion minimizing characteristics to the vessel..]. .[.52. A variable draft vessel comprising: a base structure having hydrostatic and hydrodrynamic characteristics;   a working platform;   a plurality of elements carried by said base structure with at least a portion of said elements upstanding therefrom and being connected to said platform to support said platform in spaced relation above said base structure, at least a portion of said elements including at least four stabilizing columns carried by said base structure and extending vertically a predetermined effective height between generally horizontal planes containing said platform and said base structure, a pair of said columns being located adjacent opposite ends of said base structure on opposite sides of the pitch axis of the vessel, at least two columns being located on opposite sides of the roll axis of the vessel;   the cross sectional area of said columns being substantially constant throughout the effective height thereof;   said base structure having a displacement sufficient to float the vessel in a low draft condition with the base structure having freeboard;   means for ballasting and deballasting the vessel to respectively submerge the base structure and portions of said elements below the waterline thereby to provide a high draft, otherwise unsupported, floating condition and return the vessel to the low draft condition with the base structure having freeboard;   said elements being spaced one from the other to provide an open frame area therebetween and between said platform and said base structure;   the combined water plane areas of said columns forming at least the major portion of the total water plane area of said vessel in the high draft condition;   the cross sectional areas and configuration of said columns, the weight distribution of the vessel, and the geometry of the submerged base structure and portions of said elements being such that the vessel obtains a natural period in the high draft condition no less than 6 seconds;   and means carried by the vessel for conducting drilling operations while the vessel is maintained in the high draft floating condition;   
     
     
       said vessel having a length to width ratio of at least 2 to 1..]. .[.53.  A vessel according to claim 52 including a crane for transferring loads between horizontally spaced positions..]. .[.54. A vessel according to claim 52 wherein said platform is spaced above said base structure a predetermined height at least equal to the height of the maximum anticipated wave, said columns extending vertically a predetermined effective height at least equal to the height of the maximum anticipated wave..]. .[.55. A vessel according to claim 52 wherein the natural periods in pitch and roll of the vessel lie within a range of 6 to 40 seconds..]. .[.56. A vessel according to claim 52 wherein said ballasting and deballasting means includes at least two ballast compartments carried by said base structure on each of the opposite sides of the centerline of said vessel, said two ballast compartments being horizontally spaced one from the other, and means for effecting ballast transfer into and out of said two compartments on each side of said vessel to alter the natural period of said vessel..]. .[.57. A vessel according to claim 52 wherein at least one column on eah of the opposite sides of the roll axis is oblong with its long axis extending substantially parallel to the longitudinal centerline of said vessel..]. .[.58. A variable draft column stabilized vessel comprising: a pair of elongated flotation members disposed in side-by-side spaced substantially parallel relation one to the other; a working platform;   means connected to said members and said platform to support said platform in fixed spaced relation above said members;   said connected means including at least six stabilizing columns disposed on said members and upstanding therefrom a predetermined height;   a pair of said columns being located adjacent opposite ends of said members on opposite sides of the pitch axis of said vessel, at least three columns being located on each member and on opposite sides of the roll axis of said vessel, at least one column on each member being substantially oblong in cross section and disposed such that its long axis extends substantially parallel to the longitudinal axes of the members;   the cross sectional area of said columns being substantially constant throughout the height thereof;   said members having a combined displacement sufficient to float the vessel in a low draft condition with the members having freeboard;   means for ballasting and deballasting said vessel to respectively submerge the members and portions of said connecting means below said platform below the waterline thereby to provide a high draft, otherwise unsupported, floating condition and return said vessel to the low draft condition with the members having freeboard, the displacement of the submerged members and portions of said connecting means being sufficient to maintain said vessel buoyant in the high draft floating condition;   the combined water plane areas of said columns forming at least the major portion of the total water plane area of said vessel in the high draft condition;   said connecting means being spaced one from the other to provide an open frame area between the components thereof and between said platform and said members;   and means carried by the vessel for conducting drilling operations while the vessel is maintained in the high draft floating condition..]. .[.59. A vessel according to claim 58 including a crane for transferring loads between horizontally spaced positions..]. .[.60. A vessel according to claim 58 wherein the cross sectional area and configuration of said columns, the weight distribution of the vessel and the geometry of the submerged members and portions of said connecting means are such as to provide motion minimizing characteristics to said vessel in roll, pitch and heave in the high draft condition..]. .[.61. The vessel according to claim 58 wherein said members are connected one to the other by said connecting means with the area between said members below a horizontal plane extending through said members adjacent their upper surfaces being open and substantially unobstructed..]. .[.62. A variable draft vessel according to claim 58 wherein said platform is supported in spaced relation above said members a predetermined height at least equal to the height of the maximum anticipated wave, said columns upstanding from said members an effective height at least equal to the height of the maximum anticipated wave, the displacement of said submerged members and portions of said connecting means being sufficient to maintain said vessel buoyant in the high draft condition with the mean waterline located a distance above said members at substantially one-half the effective height of said stabilizing columns..]. .[.63. A vessel according to claim 58 wherein said connecting means includes a plurality of support members forming trusses extending between said members and said platform at spaced longitudinal positions along said vessel, said trusses including transversely extending members lying adjacent the uppermost portions of said members..]. .[.64. A vessel according to claim 58 wherein each of said members has streamlined bow and stern portions to minimize resistance to movement through the water in said low draft condition..]. .[.65. A vessel according to claim 58 wherein said ballasting and deballasting means includes at least two ballast compartments in each of said members, said two ballast compartments being horizontally spaced one from the other, and means for selectively ballasting and deballasting said two compartments in each said member..]. .[.66. A vessel according to claim 58 wherein said drilling means includes a drilling mast disposed substantially along the longitudinal centerline of the vessel for supporting a drill string extending between said members..]. .[.67. A vessel according to claim 58 wherein said vessel has a length to width ratio of at least 2 to 1..]. .[.68. A vessel according to claim 58 wherein said platform is supported in spaced relation above said members a predetermined height at least equal to the height of the maximum anticipated wave, said columns upstanding from said members an effective height at least equal to the height of the maximum anticipated wave, the displacement of said submerged members and portions of said connecting means being sufficient to maintain said vessel buoyant in the high draft condition with the mean waterline located a distance above said members at substantially one-half the effective height of said stabilizing columns, said connecting means including a plurality of support members forming trusses extending between said members and said platform at spaced longitudinal positions along said vessel, said trusses including transversely extending members connectng one flotation member to the other and lying adjacent the uppermost portions of said flotation members, said ballasting and deballasting means including at least two ballast compartments in each of said flotation members, said two ballast compartments being horizontally spaced one from the other, and means for selectively ballasting and deballasting the compartments in each said member..]. .[.69. A vessel according to claim 58 wherein the centroids of said columns are spaced outboard of vertical planes containing the longitudinal axes of said members..]. .[.70. A variable draft vessel comprising: a pair of elongated flotation members disposed in side-by-side spaced substantially parallel relation one to the other;   a working platform;   means connected to said members and said platform to support said platform in fixed spaced relation above said members;   said connecting means including at least six upstanding stabilizing columns disposed on said members, a pair of said columns being located adjacent opposite ends of said members on opposite side of the pitch axis of the vessel, at least three columns being located on each member and on opposite sides of the roll axis of the vessel, the centroids of said columns being spaced outboard of vertical planes containing the longitudinal axes of said members;   the cross sectional area of said columns being substantially constant throughout the height thereof;   said members having a combined displacement sufficient to float the vessel in a low draft condition with the members having freeboard;   means for ballasting and deballasting the vessel to respectively submerge the members and portions of said connecting means below said platform below the waterline thereby to provide a high draft, otherwise unsupported, floating condition and return the vessel to the low draft condition with the members having freeboard, the displacement of the submerged members and portions of said connecting means being sufficient to maintain the vessel buoyant in the high draft floating condition;   said connecting means being spaced one from the other to provide an open frame area between the components thereof and between said platform and said members;   the combined water plane area of said columns forming at least the major portion of the total water plane area of said vessel in the high draft condition;   the cross sectional area and configuration of said columns, the weight distribution of the vessel, and the geometry of the submerged members and portions of said connecting means being such as to provide motion minimizing characteristics to said vessel in roll, pitch and heave in the high draft condition;   and means carried by the vessel for conducting drilling operations while the vessel is maintained in the high draft floating condition..]. .[.71. A vessel according to claim 70 including a crane for transferring loads between horizontally spaced positions..]. .[.72. A vessel according to claim 70 wherein the cross sectional area of said columns is substantially constant throughout the predetermined height thereof..]. .[.73. A variable draft vessel according to claim 70 wherein said platform is supported in spaced relation above said members a predetermined height at least equal to the height of the maximum anticipated wave, said columns upstanding from said members an effective height at least equal to the height of the maximum anticipated wave, the displacement of said submerged members and portions of said connecting means being sufficient to maintain said vessel buoyant in the high draft condition with the mean waterline located a distance above said members at substantially one-half the effective height of said stabilizing columns..].  .[.74. A vessel according to claim 70 wherein said ballasting and deballasting means includes at least two ballast compartments in each of said members, said two ballast compartments being horizontally spaced one from the other, and means for selectively ballasting and deballasting said two compartments in each said member..]. .[.75. A vessel according to claim 70 wherein said drilling means includes a drilling mast disposed substantially along the longitudinal centerline of the vessel for supporting a drill string extending between said members..]. .[.76. A vessel according to claim 70 wherein each of said members has streamlined bow portions to minimize resistance to movement through the water in said low draft condition..]. .[.77. A vessel according to claim 70 wherein said platform is supported in spaced relation above said members a predetermined height at least equal to the height of the maximum anticipated wave, said columns upstanding from said members an effective height at least equal to the height of the maximum anticipated wave, the displacement of said submerged members and portions of said connecting means being sufficient to maintain said vessel buoyant in the high draft condition with the mean waterline located a distance above said members at substantially one-half the effective height of said stabilizing columns, said ballasting and deballasting means including at least two ballast compartments in each of said members, said two ballast compartments being horizontally spaced one from the other, and means for selectively ballasting and deballasting said two compartments in each said member, each of said members having streamlined bow portions to minimize resistance to movement through the water in said low draft condition..]. .[.78. A variable draft vessel comprising:   a pair of discrete elongated flotation members disposed in side-by-side spaced substantially parallel relation one to the other;   a working platform;   means for supporting said platform in fixed spaced relation above said members;   said connecting means including at least six stabilizing columns disposed on said members and upstanding therefrom, a pair of said columns being located adjacent opposite ends of said members on opposite sides of the pitch axis of said vessel, at least three columns being located on each member and on opposite sides of the roll axis of said vessel;   the cross sectional area of said columns being substantially constant throughout the height thereof;   at least one of said columns on each said member being substantially oblong in cross section and disposed such that its long axis extends substantially parallel to the longitudinal axes of said members;   means for ballasting and deballasting said vessel to selectively obtain high and low draft, otherwise unsupported, floating conditions with said members and portions of said connecting means below said platform located below the waterline in the high draft floating condition, the displacement of said members and portions of said connecting means being sufficient to maintain said vessel buoyant in the high draft floating condition;   the combined water plane areas of said columns forming at least the major portion of the total water plane area of said vessel in the high draft condition; and   means carried by the vessel for conducting drilling operations while the vessel is maintained in the high draft floating condition..]. .[.79. A variable draft vessel comprising:   a pair of discrete elongated flotation members disposed in side-by-side spaced substantially parallel relation one to the other;   a working platform;   means for supporting said platform in fixed spaced relation above said members;   said connecting means including at least six stabilizing columns disposed on said members and upstanding therefrom, a pair of said columns being located adjacent opposite ends of said members on opposite sides of the pitch axis of said vessel, at least three columns being located on each member and on opposite sides of the roll axis of said vessel;   at least one of said columns on each of said member being substantially oblong in cross section and disposed such that its long axis extends substantially parallel to the longitudinal axes of said members;   and means for ballasting and deballasting said vessel to selectively obtain high and low draft conditions with said members and portions of said connecting means below said platform located below the waterline in the high draft condition, the displacement of said members and portions of said connecting means being sufficient to maintain said vessel buoyant in the high draft condition;   said columns being substantially constant in cross sectional area throughout their height, said vessel having a length to width ratio   
     
     
        greater than 2 to 1..]. .[.80.  The vessel according to claim 79 wherein the centroid of said oblong column on each said member lies outboard of vertical planes passing through the longitudinal centerlines of said member..]. .[.81. The vessel according to claim 79 wherein said ballasting and deballasting means includes at least two ballast compartments in each of said members, said two ballast compartments being horizontally spaced one from the other, and means for selectively ballasting and deballasting said two compartments in each said member..]. .[.82. The vessel according 
     
     
        to claim 79 including a derrick..]. 83. A variable draft vessel comprising: a base structure having hydrostatic and hydrodynamic characteristics;   a working platform;   a plurality of elements carried by said base structure with at least a portion of said elements upstanding therefrom and being connected to said platform to support said platform in spaced relation above said base structure, at least a portion of said elements including at least four stabilizing columns carried by said base structure and extending vertically a predetermined effective height between generally horizontal planes containing said platform and said base structure, a pair of said columns being located adjacent opposite ends of said base structure on opposite sides of the pitch axis of the vessel, at least two columns being located on opposite sides of the roll axis of the vessel;   said base structure having displacement sufficient to float the vessel in a low draft condition with the base structure having freeboard;   and means for ballasting and deballasting the vessel to respectively submerge the base structure and portions of said elements below the waterline thereby to provide a high draft condition and return the vessel with the base structure having freeboard;   said elements being spaced one from the other to provide an open frame area therebetween and between said platform and said base structure;   the cross sectional areas and configuration of said columns, the weight distribution of the vessel and the geometry of the submerged base structure and portions of said elements being such that the vessel obtains a natural period in the high draft condition no less than 6 seconds;   said vessel having a length to width ratio of at least 2 to 1;   said stabilizing .[.column.]. .Iadd.columns .Iaddend.having portions thereof which extend transversely beyond the outboard sides of said base structure thereby providing increased moment for stabilizing action about the roll axis.  .[.84. A variable draft vessel comprising:   a pair of elongated hulls disposed in side-by-side spaced substantially parallel relation one to the other;   a working platform;   means connected to said hulls and said platform to support said platform in fixed spaced relation above said hulls;   said connecting means including at least four stabilizing columns located on said hulls with a pair of said columns on each of the opposite sides of the respective pitch and roll axes of the vessel;   said platform being spaced above said hulls a predetermined height at least equal to the height of the maximum anticipated wave, said columns upstanding from said hulls a predetermined effective height at least equal to the height of the maximum anticipated wave, the cross sectional area of said columns being substantially constant throughout the effective height thereof;   said hulls having a combined displacement sufficient to float the vessel in a low draft condition with the hulls having freeboard, each of said hulls having bow and stern designs to minimize resistance to movement through the water in said low draft condition;   means for ballasting and deballasting the vessel to respectively submerge the hulls and portions of said connecting means below said platform below the waterline thereby to provide a high draft, otherwise unsupported, floating condition and return the vessel to the low draft condition with the hulls having freeboard, the displacement of the submerged hulls and portions of said connecting means being sufficient to maintain the vessel buoyant in the high draft floating condition;   said connecting means being spaced one from the other to provide an open frame area between the components thereof, and between said hulls and said platform;   the combined water plane areas of said columns forming at least the major portion of the total water plane area of said vessel in the high draft condition;   the cross sectional area and configuration of the columns, the weight distribution of the vessel, and the geometry of the submerged hulls and portions of said connecting means being such that the vessel obtains motion minimizing characteristics in the high draft condition; and   means carried by the vessel for conducting drilling operations while the vessel is maintained in the high draft floating condition..]. .Iadd. 85. A vessel according to claim 83 wherein said base structure includes a pair of elongated hulls disposed in side-by-side spaced substantially parallel relation one to the other, at least a portion of said elements including a plurality of trusses extending between said hulls and said platform and in spaced longitudinal positions along said vessel, said trusses including substantially horizontally extending members disposed adjacent uppermost portions of said hulls and restraining the hulls against lateral displacement with respect to each other..Iaddend. .Iadd. 86. A column stabilized semisubmersible vessel consisting of a pair of elongated hulls disposed in substantially parallel spaced side-by-side relation with each of said hulls spaced from and lying on an opposite side of the longitudinal centerline of said vessel, said vessel further comprising:   a working platform spaced above said hulls a predetermined height and normally lying in a generally horizontal plane;   means for supporting said platform in fixed spaced relation above said hulls including at least three pairs of upstanding columns connecting with each of said hulls and said platform; each of said columns having a substantially constant cross sectional area over the effective height of the column between the platform and associated hull;   each of said hulls having, over substantially the entire length thereof, a substantially rectangular transverse cross section with its breadth greater than its height;   a plurality of longitudinally spaced structural truss means interconnecting and reinforcing the structural relationship of the hulls, platform and columns, with such truss means including substantially transversely extending members structurally interconnecting uppermost portions of the hulls;   said vessel being generally rectangular in plan with the length of said vessel along its longitudinal centerline and roll axis being at least 2.5 times greater than the width of said vessel along its transverse centerline and pitch axis;   at least three of said columns being located on each of said two hulls on opposite sides of the vessel's roll axis with pairs of such columns being located near opposite ends of each of said hulls on opposite sides of the vessel's pitch axis and another pair of said columns being located at an intermediate position on each of said hulls;   each of said columns having an oblong cross section with a dimension extending in the direction of the vessel's longitudinal axis greater than the column's dimension extending transversely of the vessel;   the centroid of the cross section of each column on said hulls lying outboard of the longitudinal centerline of the associated hull;   the configuration and cross-sectional areas of said columns throughout effective height thereof and the distances of said columns from the vessel's longitudinal roll axis and transverse pitch axis being such that said columns maintain the vessel's metacenter above the vessel's center of gravity for all high draft semisubmerged operating positions of the vessel and also being such that said columns provide righting moment about the longitudinal roll axis which is less than righting moment provided about said transverse pitch axis when the vessel is in semisubmerged column stabilized operating positions;   said hulls having ballast compartments;   means for ballasting said vessel when required to alter its draft between a low draft hull-supported floating condition in which the hulls have freeboard with said transversely extending members structurally interconnecting uppermost portions of the hulls being disposed above the mean waterline and a high draft semisubmerged column stabilized floating and operating condition in which the mean waterline is located along intermediate portions of said columns above said hulls and below the underside of said platform;   said means for ballasting including means for adjusting vessel angle of heel change caused during semisubmerged operations to provide a reduction of the vessel's angle of heel about its roll axis when required during semisubmerged column stabilized operations; and   said means for ballasting including means for adjusting vessel angle of trim change caused during semisubmerged operations to provide a reduction of the vessel's angle of trim about its pitch axis when required during   
     
     
        semisubmerged column stabilized operations..Iaddend..Iadd. 87.  A vessel according to claim 86, wherein the ballast compartment of each of said rectangular twin hulls includes at least two separate ballast compartments spaced transversely within each hull and a plurality of separate ballast compartments spaced longitudinally within each hull..Iaddend..Iadd. 88. A vessel according to claim 86 wherein said vessel ballast means includes means for transferring ballast directly from one of said rectangular twin hulls directly to the other of said rectangular twin hulls for controlling heel of said vessel about its roll axis when required during semisubmerged column stabilized operations..Iaddend..Iadd. 89. A vessel according to claim 86, wherein: the ballast compartments of each of said rectangular twin hulls includes at last two separate ballast compartments spaced transversely within each hull and a plurality of separate ballast compartments spaced longitudinally within each hull; and said vessel ballast means also includes means for transferring ballast from at least one compartment in one hull directly to at least one compartment in the other hull for controlling the heel of said vessel about its roll axis when required during semisubmerged column stabilized operations..Iaddend. .Iadd. 90. A column stabilized semisubmersible drilling vessel comprising a vessel according to claim 86 and further comprising: a drilling rig carried by said platform;   means carried by said vessel for accommodating sufficient drilling equipment for conducting offshore drilling operations in column stabilized semisubmerged high draft condition;   said vessel ballast means including means for counteracting change in vessel angle of trim caused when said vessel is in said high draft column stabilized semisubmerged condition for drilling operations and is subjected to load change of such location and magnitude with respect to the pitch axis so that such ballast means provides when required a reduction of the vessel's angle of trim about its pitch axis during semisubmerged column stabilized drilling operations; and   said vessel ballast means also including means for similarly counteracting angle of heel caused when said vessel is in said high draft semisubmerged condition for drilling and is subjected to load change of such location and magnitude with respect to the roll axis so that such ballast means provides when required a reduction of the vessel's angle of heel about its roll axis during high draft semisubmerged column stabilized drilling operations. .Iaddend. .Iadd. 91. A vessel as in claim 86 wherein: said transversely extending members have opposite end portions overlying top surfaces of said hulls with their opposite ends connected to columns on each of said hulls near said top surfaces..Iaddend..Iadd. 92. A vessel according to claim 91 wherein: said opposite end portions of said transversely extending members are secured to said top surfaces of said hulls..Iaddend. .Iadd. 93. A column stabilized semisubmersible vessel consisting of a pair of elongated hulls disposed in substantially parallel spaced side-by-side relation with each of said hulls spaced from and lying on an opposite side of the longitudinal centerline of said vessel, said vessel further comprising:   a working platform spaced above said hulls a predetermined height and normally lying in a generally horizontal plane;   means for supporting said platform in fixed spaced relation above said hulls including at least three pairs of upstanding columns connecting with each of said hulls and said platform; each of said columns having a substantially constant cross sectional area over the effective height of the column between the platform and associated hull;   each of said hulls having an oblong transverse cross section with a breadth greater than its height and having top and bottom substantially planar parallel surfaces extending substantially the entire length of each hull, whereby such hulls configuration provides increased mass resistance to movement of said hulls and vessel through water in a vertical direction when the vessel is in high draft semisubmerged column stabilized operating condition;   a plurality of longitudinally spaced structural truss means interconnecting and reinforcing the structural relationship of the hulls, platform and columns, with such truss means including substantially transversely extending members structurally interconnecting uppermost portions of the hulls;   said vessel being generally rectangular in plan with the length of said vessel along its longitudinal centerline and roll axis being at least plural times as great as the width of said vessel along its transverse centerline and pitch axis;   at least three of said columns being located on each of said two hulls on opposite sides of the vessel's roll axis with pairs of such columns being located near opposite ends of each of said hulls on opposite sides of the vessel's pitch axis and another pair of said columns being located at an intermediate position on each of said hulls;   at least one of said columns on each said hull having an oblong cross section with a dimension extending in the direction of the longitudinal vessel axis greater than the columns' transversely extending dimension; the centroid of the cross section of such oblong columns lying outboard of the longitudinal centerline of each associated hull;   the configuration and cross-sectional areas of said columns throughout effective height thereof and the distances of said columns from the vessel's longitudinal roll axis and transverse pitch axis being such that said columns maintain the vessel's metacenter above the vessel's center of gravity for all high draft semisubmerged operating positions of the vessel and also being such that said columns provide righting moment about the longitudinal roll axis which is less than righting moment provided about said transverse pitch axis when the vessel is in semisubmerged column stabilized operating position;   said hulls having ballast compartments;   means for ballasting said vessel when required to alter its draft between a low draft hull-supported floating condition in which the hulls have freeboard with said transversely extending members structurally interconnecting uppermost portions of the hulls being disposed above the mean waterline and a high draft semisubmerged column stabilized floating and operating condition in which the mean waterline is located along intermediate portion of said columns above said hulls and below the underside of said platform;   the ballast compartments of each of said oblong twin hulls including at least two separate ballast compartments spaced transversely within each hull and a plurality of separate ballast compartments spaced longitudinally within each hull. .Iaddend..Iadd. 94. A vessel according to claim 93, wherein said means for ballasting includes means for adjusting vessel angle of heel change caused during semisubmerged operations to provide a reduction of the vessel's angle of heel about its roll axis when required during semisubmerged column stabilized operations..Iaddend..Iadd. 95. A vessel according to claim 93, wherein said means for ballasting includes means for adjusting vessel angle of trim change caused during semisubmerged operations to provide a reduction of the vessel's angle of trim about its pitch axis when required during operations of said vessel in semisubmerged column stabilized operations..Iaddend..Iadd. 96. A vessel according to claim 93, wherein said vessel ballast means includes means for transferring ballast directly from one hull to the other hull to control heel of said vessel about its roll axis during semisubmerged column stabilized operations..Iaddend..Iadd. 97. A vessel according to claim 93, wherein all of said columns have such an oblong cross section with greater dimension extending in direction of the vessel's longitudinal axis..Iaddend..Iadd. 98. A vessel according to claim 97 wherein the centroid of all of said columns lies outboard of the longitudinal centerline of each associated hull..Iaddend. .Iadd. 99. A vessel according to claim 93, wherein each of said hulls is generally rectangular in cross section..Iaddend..Iadd. 100. A vessel according to claim 93, wherein said vessel has a length to width ratio of at least 2.5 to 1..Iaddend..Iadd. 101. A vessel according to claim 93, wherein said vessel has a length which is at least 2.5 times as great as its width; each of said columns has an oblong cross section with a dimension extending in the direction of the longitudinal vessel axis greater than the column's dimension extending transversly of the vessel; the centroid of the cross section of each column on each hull lies outboard of the longitudinal centerline of the associated hull; each of said hulls is generally rectangular in cross section; and said transversely extending members structurally interconnect said hulls adjacent uppermost portions thereof..Iaddend..Iadd. 102. A vessel according to claim 101 wherein said vessel ballasting means includes means operable to transfer ballast from at least one compartment in one hull directly to at least one compartment in the other hull to control the heel of said vessel about its roll axis when required during column stabilized semisubmerged operations..Iaddend..Iadd. 103. A column stabilized semisubmersible drilling vessel comprising a vessel according to claim 93 and further comprising:   a drilling rig carried by said platform;   means carried by said vessel for accommodating sufficient drilling equipment for conducting offshore drilling operations in column stabilized semisubmerged high draft condition;   said vessel ballast means including means for counteracting change in vessel angle of trim caused when said vessel is in said high draft column stabilized semisubmerged condition for drilling operations and is subjected to load change of such location and magnitude with respect to the pitch axis so that such ballast means provides when required a reduction of the vessel's angle of trim about its pitch axis during semisubmerged column stabilized drilling operations; and   said vessel ballast means also including means for similarly counteracting angle of heel caused when said vessel is in said high draft semisubmerged condition for drilling and is subjected to load change of such location and magnitude with respect to the roll axis so that such ballast means provides when required a reduction of the vessel's angle of heel about its roll axis during high draft semisubmerged column stabilized drilling operations..Iaddend. .Iadd. 104. A vessel as in claim 93 wherein: said transversely extending members have opposite end portions overlying top surfaces of said hulls with their opposite ends connected to columns on each of said hulls near said top surfaces..Iaddend..Iadd. 105. A vessel according to claim 104 wherein: said opposite end portions of said transversely extending members are secured to said top surfaces of said hulls..Iaddend. .Iadd. 106. A column stabilized semisubmersible vessel consisting of a pair of elongated hulls disposed in substantially parallel spaced side-by-side relation with each of said hulls spaced from and lying on an opposite side of the longitudinal centerline of said vessel, said vessel further comprising;   a working platform spaced above said hulls a predetermined height and normally lying in a generally horizontal plane;   means for supporting said platform in fixed spaced relation above said hulls including at least three pairs of upstanding columns connecting with each of said hulls and said platform, each of said columns having a substantially constant cross sectional area over the effective height of the column between the platform and associated hull;   each of said hulls having an oblong transverse cross section with a breadth greater than its height and having top and bottom substantially planar parallel surfaces extending substantially the entire length of each hull;   a plurality of longitudinally spaced structural truss means interconnecting and reinforcing the structural relationship of the hulls, platform and columns, with such truss means including substantially transversely extending members structurally interconnecting uppermost portions of the hulls;   said vessel being generally rectangular in plan with the length of said vessel along its longitudinal centerline and roll axis being at least plural times as great as the width of said vessel along its transverse centerline and pitch axis;   at least three of said columns being located on each of said two hulls on opposite sides of the vessel's roll axis with pairs of such columns being located near opposite ends of each of said hulls on opposite sides of the vessel's pitch axis and another pair of said columns being located at an intermediate position on each of said hulls;   the configuration and cross-sectional areas of said columns throughout effective height thereof and the distances of said columns from the vessel's longitudinal roll axis and transverse pitch axis being such that said columns maintain the vessel's metacenter above the vessel's center of gravity for the high draft semisubmerged operating positions of the vessel and also being such that said columns provide righting moment about the longitudinal roll axis which is less than righting moment provided about said transverse pitch axis when the vessel is in semisubmerged column stabilized operating position;   said hulls having ballast compartments; and   means for ballasting said vessel when required to alter its draft between a low draft hull-supported floating condition in which the hulls have freeboard with said transversely extending members structurally interconnecting uppermost portions of the hulls being disposed above the mean waterline and a high draft semisubmerged column stabilized floating and operating condition in which the mean waterline is located along intermediate portion of said columns above said hulls and below the underside of said platform..Iaddend..Iadd. 107. A vessel according to claim 106, wherein: said means for ballasting includes means for adjusting vessel angle of heel change caused during semisubmerged operations to provide a reduction of the vessel's angle of heel about its roll axis when required during semisubmerged column stabilized operations; and   said means for ballasting also includes means for adjusting vessel angle of trim change caused during semisubmerged operations to provide a reduction of the vessel's angle of trim about its pitch axis when required during operations of said vessel in semisubmerged column stabilized   
     
     
        operations..Iaddend..Iadd. 108.  A vessel according to claim 106, wherein the ballast compartment of each of said hulls includes at least two separate ballast compartments spaced transversely within each hull and a plurality of separate ballast compartments spaced longitudinally within each hull..Iaddend..Iadd. 109. A vessel according to claim 106, wherein said vessel ballast means includes means for transferring ballast directly from one hull to the other hull to control heel of said vessel about its roll axis when required during semisubmerged column stabilized floating operations..Iaddend..Iadd. 110. A vessel according to claim 106 wherein at least one of the columns on each said hull has an oblong cross section with a dimension extending in the direction of the longitudinal vessel axis greater than the column's transversely extending dimension..Iaddend..Iadd. 111. A vessel according to claim 110 wherein all of said columns have such an oblong cross section with greater dimension extending in direction of the vessel's longitudinal axis..Iaddend..Iadd. 112. A vessel according to claim 106 wherein the centroid of the cross section of at least one column on each hull lies outboard of the longitudinal centerline of the associated hull..Iaddend..Iadd. 113. A vessel according to claim 112 wherein the centroid of all of said columns lies outboard of the longitudinal centerline of the associated hull..Iaddend..Iadd. 114. A vessel according to claim 106, wherein: each of said columns has a cross section with a dimension extending in the direction of the vessel's longitudinal axis greater than the column's dimension extending transversely of the vessel, with the centroid of the cross section of each column on each hull lying outboard of the longitudinal centerline of the associated hull..Iaddend..Iadd. 115. A vessel according to claim 106, wherein each of said hulls is generally rectangular in cross section..Iaddend..Iadd. 116. A vessel according to claim 106, wherein said vessel has a length to width ratio of at least 2.0 to 1..Iaddend..Iadd. 117. A vessel according to claim 106, wherein: said vessel has a length which is at least 2.5 times as great as its width; each of said columns has an oblong cross section with a dimension extending in the direction of the longitudinal vessel axis greater than the column's dimension extending transversely of the vessel; the centroid of the cross section of each column on each hull lies outboard of the longitudinal centerline of the associated hull; each of said hulls is generally rectangular in cross section; and said transversely extending members structurally interconnect said hulls adjacent uppermost portions thereof..Iaddend..Iadd. 118. A vessel according to claim 117, wherein: the ballst compartment of each of said hulls includes at least two separate ballast compartments spaced transversely within each hull and a plurality of separate ballast compartments spaced longitudinally of the hull; said means for ballasting includes means for adjusting vessel angle of heel change caused during semisubmerged operations to provide a reduction of the vessel's angle of heel about its roll axis when required during semisubmerged columns stabilized operations; said means for ballasting also includes means for adjusting vessel angle of trim change caused during semisubmerged operations to provide a reduction of the vessel's angle of trim about its pitch axis when required during operations of said vessel in semisubmerged column stabilized operations; and said vessel ballast means also includes means operable to transfer ballast from at least one compartment in one hull directly to at least one compartment in the other hull to control the heel of said vessel about its roll axis during semisubmerged operations..Iaddend..Iadd. 119. A vessel according to claim 106 wherein at least the upper end of said columns is modified in cross section to provide mechanical connection between the columns and the platform..Iaddend..Iadd. 120. A vessel according to claim 119, wherein said modified column cross section includes a frustoconical section..Iaddend..Iadd. 121. A vessel according to claim 106 wherein at least the lower end of said columns is modified in cross section to provide mechanical connection between the columns and the associated hulls..Iaddend..Iadd. 122. A vessel according to claim 121 wherein said modified column cross section includes a frustoconical section..Iaddend..Iadd. 123. A column stabilized semisubmersible drilling vessel comprising a vessel according to claim 106 and further comprising: a drilling rig carried by said platform;   means carried by said vessel for accommodating sufficient drilling equipment for conducting offshore drilling operations in column stabilized semisubmerged high draft condition;   said vessel ballast means including means for counteracting change in vessel angle of trim caused when said vessel is in said high draft column stabilized semisubmerged condition for drilling operations and is subjected to load change of such location and magnitude with respect to the pitch axis so that such ballast means provides when required a reduction of the vessel's angle of trim about its pitch axis during semisubmerged column stabilized drilling operations; and   said vessel ballast means also including means for similarly counteracting angle of heel caused when said vessel is in said high draft semisubmerged condition for drilling and is subjected to load change of such location and magnitude with respect to the roll axis so that such ballast means provides when required a reduction of the vessel's angle of heel about its roll axis during high draft semisubmerged column stabilized drilling operations..Iaddend..Iadd. 124. A vessel as in claim 106, wherein the centroids of the water plane areas defined by the cross sections of the columns are located outboard of the centerlines of the hulls an extended distance from the centerline of the vessel on opposite sides of the longitudinally extending roll axis to develop larger moments of intertia of the water plane area about the roll axis (than would otherwise be the case if the longitudinal centerlines of said hulls and their associated columns were coincident)..Iaddend..Iadd. 125. A vessel as in claim 106, wherein the vessel has six columns including three columns on each hull, with one middle pair of columns located adjacent the vessel's transverse pitch axis and with two other pairs of columns located adjacent the vessel's transverse pitch axis and with two other pairs of columns on opposite sides of the vessel pitch axis in generally symmetrical relation thereto near opposite ends of the associated hulls..Iaddend..Iadd. 126. A vessel as in claim 106, wherein: the vessel has a total odd number of pairs of columns and the middle pair of columns is located adjacent the vessel's pitch axis, with the remaining pairs of columns being disposed in equal numbers on opposite sides of the vessel pitch axis and with two pairs of columns located near opposite ends of said hulls..Iaddend..Iadd. 127. A vessel as in claim 106, wherein: the vessel has a total even number of pairs of columns and the middle two pairs of columns are located on opposite sides of and near the transverse pitch axis; the remaining pairs of said columns being located outwardly of said middle pairs of columns and including two pairs of each columns on the hulls near opposite ends of said hulls..Iaddend..Iadd. 128. A vessel as claimed in claim 106, wherein said stabilizing columns have outboard portions thereof which extend transversely beyond the outboard sides of the respective hulls..Iaddend. .Iadd. 129. A vessel as in claim 106 wherein: said transversely extending members have opposite end portions overlying top surfaces of said hulls with their opposite ends connected to columns on each of said hulls near said top surfaces..Iaddend..Iadd. 130. A vessel according to claim 129 wherein: said opposite end portions of said transversely extending members are secured to said top surfaces of said hulls..Iaddend. .Iadd. 131. A column stabilized semisubmersible vessel consisting of a pair of elongated hulls disposed in substantially parallel spaced side-by-side relation with each of said hulls spaced from and lying on an opposite side of the longitudinal centerline of said vessel, said vessel further comprising:   a working platform spaced above said hulls a predetermined height and lying in a generally horizontal plane;   means for supporting said platform in fixed spaced relation above said hulls including at least three pairs of upstanding columns connecting with each of said hulls and said platform;   each of said columns having a substantially constant cross sectional area over the effective height of the column between the platform and associated hull;   each of said hulls having an oblong transverse cross section with a breadth greater than its height and having top and bottom substantially planar parallel surfaces extending substantially the entire length of each hull, whereby such hull's configuration provides increased mass resistance to movement of said hulls and vessel through water in a vertical direction when the vessel is in high draft semisubmerged column stabilized operating condition;   a plurality of longitudinally spaced structural truss means interconnecting and reinforcing the structural relationship of the hulls, platform and columns, with such truss means including substantially transversely extending members structurally interconnecting uppermost portions of the hulls;   said vessel being generally rectangular in plan with the length of said vessel along its longitudinal centerline and roll axis being substantially greater than the width of said vessel along its transverse centerline and pitch axis;   at least three of said columns being located on each of said two hulls on opposite sides of the vessel's roll axis with pairs of such columns being located near opposite ends of each of said hulls on opposite sides of the vessel's pitch axis and another pair of said columns being located at an intermediate position on each of said hulls;   the configuration and cross-sectional areas of said columns throughout effective height thereof and the distances of said columns from the vessel's longitudinal roll axis and transverse pitch axis being such that said columns maintain the vessel's metacenter above the vessel's center of gravity for all high draft semisubmerged operating positions of the vessel and also being such that said columns provide righting moment about the longitudinal roll axis which is less than righting moment provided about said transverse pitch axis when the vessel is in semisubmerged column stabilized operating position;   said hulls having ballast compartments;   means for ballasting said vessel when required to alter its draft between a low draft hull-supported floating condition in which the hulls have freeboard with said transversely extending members structurally interconnecting uppermost portions of the hulls being disposed above the mean waterline and a high draft semisubmerged column stabilized floating and operating condition in which the mean waterline is located along intermediate portion of said columns above said hulls and below the underside of said platform;   said means for ballasting including means for adjusting vessel angle of heel change caused during semisubmerged operations to provide a reduction of the vessel's angle of heel about its roll axis when required during semisubmerged column stabilized operations; and   said means for ballasting including means for adjusting vessel angle of trim change caused during semisubmerged operations to provide a reduction of the vessel's angle of trim about its pitch axis when required during   
     
     
        semisubmerged column stabilized operations. .Iaddend..Iadd. 132.  A vessel according to claim 131, wherein the ballast compartment of each of said hulls includes at least two separate ballast compartments spaced transversely within each hull and a plurality of separate ballast compartments spaced longitudinally within each hull. .Iaddend..Iadd. 133. A vessel according to claim 131, wherein said vessel ballast means includes means for transferring ballast directly from one hull to the other hull to control heel of said vessel about its roll axis when required during semisubmerged column stabilized floating operations. .Iaddend..Iadd. 134. A vessel according to claim 131 wherein each of said columns on said hulls has an oblong cross section with a dimension extending in the direction of the longitudinal vessel axis greater than the column's transversely extending dimension. .Iaddend..Iadd. 135. A vessel according to claim 131, wherein the centroid of the cross section of each of the columns on each hull lies outboard of the longitudinal centerline of the associated hull. .Iaddend. .Iadd. 136. A vessel according to claim 131, wherein each of said columns has a cross section with a dimension extending in the direction of the vessel's longitudinal axis greater than the column's dimension extending transversely of the vessel; with the centroid of the cross section of each column on each hull lying outboard of the longitudinal centerline of the associated hull. .Iaddend..Iadd. 137. A vessel according to claim 131, wherein each of said hulls is generally rectangular in cross section. .Iaddend..Iadd. 138. A vessel according to claim 131, wherein said vessel has a length to width ratio of at least 2.5 to 1. .Iaddend..Iadd. 139. A vessel according to claim 131, wherein said vessel has a length which is at least plural times as great as its width; each of said columns has an oblong cross section with a dimension extending in the direction of the longitudinal vessel axis greater than the column's dimension extending transversely of the vessel; the centroid of the cross section of each column on each hull lies outboard of the longitudinal centerline of the associated hull; each of said hulls is generally rectangular in cross section; and said transversely extending members structurally interconnect said hulls adjacent uppermost portions thereof. .Iaddend..Iadd. 140. A vessel according to claim 139, wherein the ballast compartments of each of said hulls includes at least two separate ballast compartments spaced transversely within each hull and a plurality of separate ballast compartments spaced longitudinally of the hull; and said vessel also includes ballast means operable to transfer ballast from at least one compartment in one hull directly to at least one compartment in the other hull to control the heel of said vessel about its roll axis during semisubmerged operations. .Iaddend. .Iadd. 141. A column stabilized semisubmersible drilling vessel comprising a vessel according to claim 131 and further comprising: a drilling rig carried by said platform;   means carried by said vessel for accommodating sufficient drilling equipment for conducting offshore drilling operations in column stabilized semisubmerged high draft condition;   said vessel ballast means including means for counteracting change in vessel angle of trim caused when said vessel is in said high draft column stabilized semisubmerged condition for drilling operations and is subjected to load change at such location and magnitude with respect to the pitch axis so that such ballast means provides when required a reduction of the vessel's angle of trim about its pitch axis during semisubmerged column stabilized drilling operations, and   said vessel ballast means also including means for similarly counteracting angle of heel caused when said vessel is in said high draft semisubmerged condition for drilling and is subjected to load change of such location and magnitude with respect to the roll axis so that such ballast means provides when required a reduction of the vessel's angle of heel about its roll axis during high draft semisubmerged column stabilized drilling operations. .Iaddend. .Iadd. 142. A vessel as in claim 131 wherein: said transversely extending members have opposite end portions overlying top surfaces of said hulls with their opposite ends connected to columns on each of said hulls near said top surfaces. .Iaddend..Iadd. 143. A vessel according to claim 142 wherein: said opposite end portions of said transversely extending members are secured to said top surfaces of said hulls.