Dredge cutterhead

Abstract

A dredge cutterhead has a plurality of helical arms inter-connecting a hub and a ring. Each of the arms has a front leading edge for attachment of cutting teeth. In one aspect, each of the arms has a trough portion, and the arm is shaped such that dredged material is directed toward the ring along the center of the trough portion. In another aspect, the ring of the cutterhead defines an annular channel for receiving loosened material.

What is claimed is: 
     
       1. A dredge cutterhead comprising:
 (a) a hub, a ring, and a plurality of helical arms interconnecting said hub and said ring; 
 (b) each of said helical arms having a leading edge for attachment of cutting teeth, and a trailing edge, and at least some of the helical arms being driving helical arms each having a trough portion located between said leading and trailing edges and extending along said driving helical arm toward said ring, each said trough portion being substantially free from structures obstructing movement of material along said driving helical arm toward said ring, and each said trough portion having a degree of curvature of between about 10% to about 25%; and 
 (c) each of said driving helical arms being shaped such that said leading edge of a part of a respective driving helical arm near said ring trails behind said leading edge of a part of said respective helical arm near said hub as said cutterhead is rotated about a rotational axis thereof, and a net force exerted on dredged material in said trough portion pushes said material toward said ring generally along the center of said trough portion as said cutterhead is rotated. 
 
     
     
       2. The dredge cutterhead of  claim 1  wherein each of said driving helical arms has a degree of curvature that generally increases along at least a respective portion of each of said driving helical arms that is nearer to said ring than to said hub. 
     
     
       3. The dredge cutterhead of  claim 1  wherein each of said driving helical arms has a maximum degree of curvature and a minimum degree of curvature, and wherein said maximum degree of curvature is located nearer to said ring than is said minimum degree of curvature. 
     
     
       4. The dredge cutterhead of  claim 1  wherein each of said driving helical arms has a degree of curvature near said ring and a degree of curvature near said hub, and wherein said degree of curvature near said ring is at least 1.5 times as great as said degree of curvature near said hub. 
     
     
       5. The dredge cutterhead of  claim 1  wherein each of said driving helical arms is wider near said ring than near said hub. 
     
     
       6. The dredge cutterhead of  claim 1  herein wherein each said leading edge has a helix angle of at least 140° near said ring. 
     
     
       7. The dredge cutterhead of  claim 1  wherein said cutterhead has an aspect ratio of at least 2.0. 
     
     
       8. The dredge cutterhead of  claim 1  wherein each said trough portion is thinner than a leading portion of each of said driving helical arms. 
     
     
       9. The dredge cutterhead of  claim 1  wherein said ring further defines a plurality of notches, each of said notches communicating with a respective trough portion. 
     
     
       10. The dredge cutterhead of  claim 1  wherein said trailing edge of each said driving helical arm curves inwardly into the interior of said cutterhead. 
     
     
       11. The dredge cutterhead of  claim 1  wherein said ring defines a channel extending annularly along an interior of said ring and facing openly inward from said ring toward said rotational axis of said cutterhead. 
     
     
       12. A dredge cutterhead comprising:
 (a) a hub, a ring and a plurality of helical arms interconnecting said hub and said ring;   (b) each of said helical arms having a leading edge for attachment of cutting teeth, a trailing edge, and a trough portion located between said leading and trailing edges and extending along said helical arm toward said ring, said trough portion being free from structures obstructing movement of material along said helical arm toward said ring; and   (c) each of said helical arms having a degree of curvature near said ring of at least 15%.   
     
     
       13. The dredge cutterhead of  claim 12  wherein said degree of curvature generally increases over at least a respective portion of each of said helical arms that is located nearer to said ring than to said hub. 
     
     
       14. The A dredge cutterhead of  claim 12  comprising:
 (a) a hub, a ring and a plurality of helical arms interconnecting said hub and said ring; 
 (b) each of said helical arms having a leading edge and a trailing edge, and a plurality of the helical arms being driving helical arms each having a trough portion located on an inner side of the driving helical arm between said leading and trailing edges and extending along said driving helical arm toward said ring, each said trough portion being free from structures obstructing movement of material along said driving helical arm toward said ring; and 
 (c) each of said driving helical arms having a degree of curvature that is larger near said ring than near said hub and which has a degree of curvature near said ring of at least 15%, wherein each of said driving helical arms has a minimum and a maximum degree of curvature that are different, and wherein said maximum degree of curvature is located nearer to said ring than is said minimum degree of curvature. 
 
     
     
       15. The dredge cutterhead of  claim 14  wherein said minimum degree of curvature is near said hub and said maximum degree of curvature is near said ring. 
     
     
       16. The A dredge cutterhead of  claim 12  comprising:
 (a) a hub, a ring and a plurality of helical arms interconnecting said hub and said ring; 
 (b) each of said helical arms having a leading edge and a trailing edge, and a plurality of the helical arms being driving helical arms each having a trough portion located on an inner side of the driving helical arm between said leading and trailing edges and extending along said driving helical arm toward said ring, each said trough portion being free from structures obstructing movement of material along said driving helical arm toward said ring; and 
 (c) each of said driving helical arms having a degree of curvature that is larger near said ring than near said hub and which has a degree of curvature near said ring of at least 15%, wherein said degree of curvature at a location near said ring is at least 1.5 times as great as said degree of curvature at another location near said hub for each said driving helical arm. 
 
     
     
       17. The A dredge cutterhead of  claim 12  comprising:
 (a) a hub, a ring and a plurality of helical arms interconnecting said hub and said ring; 
 (b) each of said helical arms having a leading edge and a trailing edge, and a plurality of the helical arms being driving helical arms each having a trough portion located on an inner side of the driving helical arm between said leading and trailing edges and extending along said driving helical arm toward said ring, each said trough portion being free from structures obstructing movement of material along said driving helical arm toward said ring; and 
 (c) each of said driving helical arms having a degree of curvature that is larger near said ring than near said hub and which has a degree of curvature near said ring of at least 15%, wherein each of said driving helical arms is wider near said ring than near said hub. 
 
     
     
       18. The A dredge cutterhead of  claim 12  comprising:
 (a) a hub, a ring and a plurality of helical arms interconnecting said hub and said ring; 
 (b) each of said helical arms having a leading edge and a trailing edge, and a plurality of the helical arms being driving helical arms each having a trough portion located on an inner side of the driving helical arm between said leading and trailing edges and extending along said driving helical arm toward said ring, each said trough portion being free from structures obstructing movement of material along said driving helical arm toward said ring; and 
 (c) each of said driving helical arms having a degree of curvature that is larger near said ring than near said hub and which has a degree of curvature near said ring of at least 15%, 
 
       wherein each said leading edge has a helix angle of at least 140° near said ring. 
     
     
       19. The A dredge cutterhead of  claim 12  comprising:
 (a) a hub, a ring and a plurality of helical arms interconnecting said hub and said ring; 
 (b) each of said helical arms having a leading edge and a trailing edge, and a plurality of the helical arms being driving helical arms each having a trough portion located on an inner side of the driving helical arm between said leading and trailing edges and extending along said driving helical arm toward said ring, each said trough portion being free from structures obstructing movement of material along said driving helical arm toward said ring; and 
 (c) each of said driving helical arms having a degree of curvature that is larger near said ring than near said hub and which has a degree of curvature near said ring of at least 15%, wherein said cutterhead has an aspect ratio of at least 1.7. 
 
     
     
       20. The dredge cutterhead of claim  12  14 wherein said trough portion is thinner than a leading portion of each said driving helical arm. 
     
     
       21. The dredge cutterhead of claim  12  14 wherein said ring further defines a plurality of notches, each of said notches communicating with a respective trough portion. 
     
     
       22. The dredge cutterhead of claim  12  14 wherein said trailing edge of each said driving helical arm curves inwardly into the interior of said cutterhead. 
     
     
       23. The A dredge cutterhead of  claim 12  comprising:
 (a) a hub, a ring and a plurality of helical arms interconnecting said hub and said ring; 
 (b) each of said helical arms having a leading edge and a trailing edge, and a plurality of the helical arms being driving helical arms each having a trough portion located on an inner side of the driving helical arm between said leading and trailing edges and extending along said driving helical arm toward said ring, each said trough portion being free from structures obstructing movement of material along said driving helical arm toward said ring; and 
 (c) each of said driving helical arms having a degree of curvature that is larger near said ring than near said hub and which has a degree of curvature near said ring of at least 15%, wherein said ring defines a channel extending annularly along an interior of said ring and facing openly inward from said ring toward a rotational axis of said cutterhead. 
 
     
     
       24. A dredge cutterhead comprising:
 (a) a hub, a ring and a plurality of helical arms interconnecting said hub and said ring; 
 (b) each of said helical arms being capable of supporting a plurality of cutting teeth; and 
 (c) said ring defining a channel extending annularly along an interior of said ring and facing openly inward from said ring toward a rotational axis of said cutterhead for retaining loosened material. 
 
     
     
       25. The dredge cutterhead of  claim 24  wherein said channel has a cross-section in the shape of a half-pipe. 
     
     
       26. The dredge cutterhead of  claim 24  wherein at least one of said helical arms has a trough portion extending therealong toward said ring. 
     
     
       27. The dredge cutterhead of  claim 26  wherein said ring defines a notch in communication with said trough portion and said channel. 
     
     
       28. A dredge cutterhead comprising:
 (a) a hub, a ring defining an annular channel having a cross-section in the shape of a half-pipe, and a plurality of helical arms interconnecting said hub and said ring;   (b) each of said helical arms having a leading edge for attachment of cutting teeth, a trailing edge, and a trough portion therebetween; and   (c) each of said helical arms having a degree of curvature near said ring of at least 10%.   
     
     
       29. The A dredge cutterhead of  claim 28  comprising:
 (a) a hub, a ring defining an annular channel having a cross-section in the shape of a half-pipe, and a plurality of helical arms interconnecting said hub and said ring; 
 (b) each of said helical arms having a leading edge for attachment of cutting teeth, a trailing edge, and a trough portion therebetween; and 
 (c) each of said helical arms having a degree of curvature near said ring of at least 10%, wherein said ring defines a notch in communication with said trough portion and said channel. 
 
     
     
       30. A dredge cutterhead comprising:
 (a) a hub, a ring and a plurality of helical arms interconnecting said hub and said ring;   (b) each of said helical arms being capable of supporting a plurality of cutting teeth; and   (c) said ring defining an interior annular channel having a cross-section in the shape of a halfpipe, for retaining loosened material.   
     
     
       31. The dredge cutterhead of  claim 30  wherein at least one of said helical arms has a trough portion. 
     
     
       32. The A dredge cutterhead of  claim 31  comprising:
 (a) a hub, a ring and a plurality of helical arms interconnecting said hub and said ring; 
 (b) each of said helical arms being capable of supporting a plurality of cutting teeth, wherein at least one of said helical arms has a trough portion; and 
 (c) said ring defining an interior annular channel having a cross-section in the shape of a half-pipe for retaining loosened material, wherein said ring defines a notch in communication with said trough portion and said channel. 
 
     
     
       33. A dredge cutterhead comprising:
 (a) a hub, a ring, and a plurality of helical arms interconnecting said hub and said ring; 
 (b) each of said helical arms having a leading edge for attachment of cutting teeth, a trailing edge, and a trough portion therebetween; and 
 (c) each of said helical arms having a degree of curvature that generally increases along at least a portion of each of said helical arms that is located nearer to said ring than to said hub and being shaped such that a net force exerted on dredged material in said trough portion pushes said material toward said ring generally along the center of said trough portion. 
 
     
     
       34. A dredge cutterhead comprising:
 (a) a hub, a ring, and a plurality of helical arms interconnecting said hub and said ring; 
 (b) each of said helical arms having a leading edge for attachment of cutting teeth, a trailing edge, and a trough portion therebetween; and 
 (c) each of said helical arms having a maximum degree of curvature and a minimum degree of curvature which are different, and said maximum degree of curvature being located nearer to said ring than said minimum degree of curvature is located, and each of said helical arms being shaped such that a net force exerted on dredged material in said trough portion pushes said material toward said ring generally along the center of said trough portion. 
 
     
     
       35. A dredge cutterhead comprising:
 (a) a hub, a ring, and a plurality of helical arms interconnecting said hub and said ring; 
 (b) each of said helical arms having a leading edge for attachment of cutting teeth, a trailing edge, and a trough portion therebetween; 
 (c) each of said helical arms being shaped such that a net force exerted on dredged material in said trough portion pushes said material toward said ring generally along the center of said trough portion; and 
 (d) each of said helical arms having a degree of curvature near said ring and a degree of curvature near said hub, said degree of curvature near said ring being at least 1.5 times as great as said degree of curvature near said hub. 
 
     
     
       36. A dredge cutterhead comprising:
 (a) a hub, a ring, and a plurality of helical arms interconnecting said hub and said ring; 
 (b) each of said helical arms having a leading portion, a leading edge for attachment of cutting teeth, a trailing edge, and a trough portion between said leading edge and said trailing edge, and said trough portion being thinner than said leading portion; and 
 (c) each of said helical arms being shaped such that a net force exerted on dredged material in said trough portion pushes said material toward said ring generally along the center of said trough portion. 
 
     
     
       37. A dredge cutterhead comprising:
 (a) a hub, a ring, and a plurality of helical arms interconnecting said hub and said ring; 
 (b) each of said helical arms having a leading edge for attachment of cutting teeth, a trailing edge, and a trough portion therebetween; 
 (c) each of said helical arms being shaped such that a net force exerted on dredged material in said trough portion pushes said material toward said ring generally along the center of said trough portion; and 
 (d) said ring defining a plurality of notches, each of said notches communicating with a respective trough portion. 
 
     
     
       38. A dredge cutterhead comprising:
 (a) a hub, a ring and a plurality of helical arms interconnecting said hub and said ring;   (b) each of said helical arms having a leading edge for attachment of cutting teeth, a trailing edge, and a trough portion therebetween; and   (c) each of said helical arms having a degree of curvature that generally increases over at least a portion of said arm that is located nearer to said ring than to said hub, and said degree of curvature near said ring being at least 10%.   
     
     
       39. A dredge cutterhead comprising:
 (a) a hub, a ring and a plurality of helical arms interconnecting said hub and said ring; 
 (b) each of said helical arms having a leading edge for attachment of cutting teeth, a trailing edge, and a trough portion therebetween; 
 (c) each of said helical arms having a minimum degree of curvature and a maximum degree of curvature which are different, said maximum degree of curvature being located nearer to said ring than is said minimum degree of curvature; and 
 (d) each of said helical arms having a degree of curvature near said ring of at least 10%. 
 
     
     
       40. The dredge cutterhead of  claim 39  wherein said minimum degree of curvature is near said hub and said maximum degree of curvature is near said ring. 
     
     
       41. A dredge cutterhead comprising:
 (a) a hub, a ring and a plurality of helical arms interconnecting said hub and said ring; 
 (b) each of said helical arms having a leading edge for attachment of cutting teeth, a trailing edge, and a trough portion therebetween; and 
 (c) each of said helical arms having a degree of curvature, said degree of curvature at a location near said ring being at least 1.5 times as great as said degree of curvature at another location near said hub, and said degree of curvature near said ring being at least 10%. 
 
     
     
       42. A dredge cutterhead comprising:
 (a) a hub, a ring and a plurality of helical arms interconnecting said hub and said ring; 
 (b) each of said helical arms having a leading portion, a leading edge for attachment of cutting teeth, a trailing edge, and a trough portion between said leading edge and said trailing edge, and said trough portion being thinner than said leading portion; and 
 (c) each of said helical arms having a degree of curvature near said ring of at least 10%. 
 
     
     
       43. A dredge cutterhead comprising:
 (a) a hub, a ring and a plurality of helical arms interconnecting said hub and said ring; 
 (b) each of said helical arms having a leading edge for attachment of cutting teeth, a trailing edge, and a trough portion therebetween; 
 (c) each of said helical arms having a degree of curvature near said ring of at least 10%; and 
 (d) said ring defining a plurality of notches, each of said notches communicating with a respective trough portion. 
 
     
     
       44. The dredge cutterhead of claim 1 wherein all the helical arms are said driving helical arms. 
     
     
       45. The dredge cutterhead of claim 14 wherein all the helical arms are said driving helical arms. 
     
     
       46. The dredge cutterhead of claim 29 wherein the degree of curvature of each of the helical arms is smaller than about 25%. 
     
     
       47. A dredge cutterhead comprising:
 (a) a hub, a ring and a plurality of helical arms interconnected said hub and said ring; and   (b) said ring defining a channel extending annularly along an interior of said ring and facing openly inward from said ring toward a rotational axis of said cutterhead for retaining loosened material.   
     
     
       48. A dredge cutterhead comprising:
 (a) a hub, a ring, and a plurality of helical arms interconnecting said hub and said ring;   (b) each of said helical arms having a leading edge and a trailing edge, and a plurality of the helical arms being driving helical arms each having a trough portion between the leading and trailing edges; and   (c) each of said driving helical arms having a degree of curvature that generally increases along at least a portion of each of said driving helical arms that is located nearer to said ring than to said hub and being shaped such that a net force exerted on dredged material in said trough portion pushes said material toward said ring along said trough portion as the cutterhead is rotated.   
     
     
       49. A dredge cutterhead in accordance with claim 48 wherein the degree of curvature near the ring for each said driving helical arm is at least 10%. 
     
     
       50. A dredge cutterhead comprising:
 (a) a hub, a ring, and a plurality of helical arms interconnecting said hub and said ring;   (b) each of said helical arms having a leading edge and a trailing edge, and a plurality of the helical arms being driving helical arms each having a trough portion between the leading and trailing edges; and   (c) each of said driving helical arms having a maximum degree of curvature and a minimum degree of curvature which are different, and said maximum degree of curvature being located nearer to said ring than said minimum degree of curvature is located, and each of said driving helical arms being shaped such that a net force exerted on dredged material in said trough portion pushes said material toward said ring along said trough portion as the cutterhead is rotated.   
     
     
       51. A dredge cutterhead comprising:
 (a) a hub, a ring, and a plurality of helical arms interconnecting said hub and said ring;   (b) each of said helical arms having a leading edge and a trailing edge, and a plurality of the helical arms being driving helical arms each having a trough portion between the leading and trailing edges;   (c) each of said driving helical arms being shaped such that a net force exerted on dredged material in said trough portion pushes said material toward said ring along said trough portion as the cutterhead is rotated; and   (d) each of said driving helical arms having a degree of curvature near said ring and a degree of curvature near said hub, said degree of curvature near said ring being at least 1.5 times as great as said degree of curvature near said hub.   
     
     
       52. A dredge cutterhead comprising:
 (a) a hub, a ring, and a plurality of helical arms interconnecting said hub and said ring;   (b) each of said helical arms having a leading portion and a trailing edge, and a plurality of the helical arms being driving helical arms each having a trough portion between said leading edge and said trailing edge, and said trough portion being thinner than said leading portion; and   (c) each of said driving helical arms being shaped such that a net force exerted on dredged material in said trough portion pushes said material toward said ring generally along the center of said trough portion.   
     
     
       53. A dredge cutterhead in accordance with claim 52 wherein each of said driving helical arms having a degree of curvature near said ring of at least 10%. 
     
     
       54. A dredge cutterhead comprising:
 (a) a hub, a ring, and a plurality of helical arms interconnecting said hub and said ring;   (b) each of said helical arms having a leading edge and a trailing edge, and a plurality of the helical arms being driving helical arms each having a trough portion between the leading and trailing edges;   (c) each of said driving helical arms being shaped such that a net force exerted on dredged material in said trough portion pushes said material toward said ring along said trough portion as the cutterhead is rotated; and   (d) said ring defining a plurality of notches, each of said notches communicating with a respective trough portion.   
     
     
       55. A dredge cutterhead comprising:
 (a) a hub, a ring, and a plurality of helical arms interconnecting said hub and said ring, said dredge cutterhead having an aspect ratio of at least 1.4;   (b) each of said helical arms having a leading edge and a trailing edge, a plurality of the helical arms being driving helical arms each having a trough portion located between said leading and trailing edges and extending along said driving helical arm toward said ring, said trough portion being substantially free from structures obstructing movement of material along said driving helical arm toward said ring; and   (c) each of said driving helical arms being shaped such that said leading edge of a part of a respective driving helical arm near said ring trails behind said leading edge of a part of said respective helical arm near said hub as said cutterhead is rotated about a rotational axis thereof, and a net force exerted on dredged material in said trough portion pushes said material toward said ring along said trough portion as said cutterhead is rotated.   
     
     
       56. A dredge cutterhead in accordance with claim 55 wherein the aspect ratio is at least 1.7. 
     
     
       57. A dredge cutterhead in accordance with claim 56 wherein each said helical arm is a driving helical arm. 
     
     
       58. A dredge cutterhead in accordance with claim 55 wherein the aspect ratio is at least 2. 
     
     
       59. A dredge cutterhead comprising:
 (a) a hub, a ring, and a plurality of helical arms interconnecting said hub and said ring;   (b) each of said helical arms having a leading edge and a trailing edge, a plurality of the helical arms being driving helical arms each having a trough portion located between said leading and trailing edges and extending along said driving helical arm toward said ring, each said trough portion being substantially free from structures obstructing movement of material along said driving helical arm toward said ring, and each said trough portion having a pair of ends that curve inward relative to a central portion of the trough portion; and   (c) each of said driving helical arms being shaped such that said leading edge of a part of a respective driving helical arm near said ring trails behind said leading edge of a part of said respective helical arm near said hub as said cutterhead is rotated about a rotational axis thereof, and a net force exerted on dredged material in said trough portion pushes said material toward said ring along said trough portion as said cutterhead is rotated.   
     
     
       60. A dredge cutterhead comprising:
 (a) a hub, a ring, and a plurality of helical arms interconnecting said hub and said ring;   (b) each of said helical arms having a leading edge and a trailing edge, a plurality of the helical arms being driving helical arms each having a trough portion located between said leading and trailing edges, and a leading portion between the leading edge and the trough portion, the leading portion having a width that is within 10% to 35% of the width of the entire driving helical arm, and the trough portion extending along each said driving helical arm toward said ring, each said trough portion being substantially free from structures obstructing movement of material along said driving helical arm toward said ring; and   (c) each of said driving helical arms being shaped such that said leading edge of a part of a respective driving helical arm near said ring trails behind said leading edge of a part of said respective helical arm near said hub as said cutterhead is rotated about a rotational axis thereof, and a net force exerted on dredged material in said trough portion pushes said material toward said ring along said trough portion as said cutterhead is rotated.   
     
     
       61. A dredge cutterhead comprising:
 (a) a hub, a ring, and a plurality of helical arms interconnecting said hub and said ring;   (b) each of said helical arms having a leading edge and a trailing edge, a plurality of the helical arms being driving helical arms each having a trough portion located between said leading and trailing edges and extending along said driving helical arm toward said ring, each said trough portion being substantially free from structures obstructing movement of material along said driving helical arm toward said ring; and   (c) each of said driving helical arms being shaped such that a width of each said driving helical arm generally increases from the hub to the ring said leading edge of a part of a respective driving helical arm near said ring trails behind said leading edge of a part of said respective helical arm near said hub as said cutterhead is rotated about a rotational axis thereof, and a net force exerted on dredged material in said trough portion pushes said material toward said ring along said trough portion as said cutterhead is rotated.   
     
     
       62. A dredge cutterhead comprising:
 (a) a hub, a ring, and a plurality of helical arms interconnecting said hub and said ring;   (b) each of said helical arms having a leading edge and a trailing edge, and a plurality of the helical arms being driving helical arms each having a trough portion located between said leading and trailing edges and extending along said driving helical arm toward said ring, each said trough portion being substantially free from structures obstructing movement of material along said driving helical arm toward said ring; and   (c) each of said driving helical arms being shaped such that (i) said leading edge of a part of a respective driving helical arm near said ring trails behind said leading edge of a part of said respective helical arm near said hub as said cutterhead is rotated about a rotational axis thereof, (ii) said trough portion at the trailing end being directed inward and downward to retain dredged material in the trough portion, and (iii) a net force exerted on dredged material in said trough portion pushes said material toward said ring along said trough portion as said cutterhead is rotated.   
     
     
       63. A dredge cutterhead comprising:
 (a) a hub, a ring, and a plurality of helical arms interconnecting said hub and said ring;   (b) each of said helical arms having a leading edge and a trailing edge, said leading edge of each said helical arm near said ring trailing behind said leading edge of said helical arm near said hub as said cutterhead is rotated about a rotational axis, the leading edge being adapted to dig into the ground as the cutterhead is rotated, the arm traversing an arcuate path through the ground with each rotation of the cutterhead such that the leading edge initially moves downward into the ground and then upward out of the ground with each rotation about the rotational axis;   (c) the helical arms being positioned with gaps between each adjacent pair of arms through which dredged material passes into the cutterhead as the helical arms move through the ground; and   (d) a plurality of the helical arms being driving helical arms each having a trough portion located between said leading and trailing edges and extending along said driving helical arm toward said ring, each said trough portion facing generally inward and shaped with inturned sides to retain dredged material passing through the respective gap as the driving helical arm moves upward out of the ground, and each said trough portion being substantially free from structures obstructing movement of the dredged material retained in each said trough portion along said driving helical arm toward said ring; and   (e) said trough portion in each said driving helical arm being shaped along the length thereof such that gravity, buoyancy, and centrifugal forces caused by rotation of the cutterhead pushes the dredged material in said trough portion along the length of the trough portion to the ring as the arm moves upward out of the ground with each rotation of the cutterhead.   
     
     
       64. A dredge cutterhead comprising:
 (a) a hub, a ring, and a plurality of helical arms interconnecting said hub and said ring;   (b) each of said helical arms having a leading edge and a trailing edge, and a plurality of the helical arms being driving helical arms each having a trough portion located between said leading and trailing edges and extending along said driving helical arm toward said ring, each said trough portion being substantially free from structures obstructing movement of material along said driving helical arm toward said ring; and   (c) each of said driving helical arms being shaped such that said leading edge of a part of a respective driving helical arm near said ring trails behind said leading edge of a part of said respective helical arm near said hub as said cutterhead is rotated about a rotational axis thereof, and a net force exerted on dredged material in said trough portion pushes said material along said trough portion as said cutterhead is rotated to and inward of said ring for collection into a suction pipe.