A propulsion device

Abstract

A blade (300) for a rowing oar (100), comprises: a first lifting element (310a) having a first chord line (320a) at a first point along its span, the first chord line extending from a trailing edge (340a) to a leading edge (330a) of the first lifting element; a second lifting element (310b) having a second chord line (320b) at a second point along its span, the second chord line extending from a trailing edge (340b) to a leading edge (330b) of the second lifting element; and a slot (370a) through which water may flow when in use, the slot (370a) having a constant width across more than half of the slot's length. The constant width extends between the trailing edge of the second lifting element (340b) and the nearest point on the first lifting element. The first and the second chord lines (340a, 340b) are non-parallel so as to form a first angle (550b) therebetween.

1 . A blade for a rowing oar, the blade comprising:
 a first lifting element having a first chord line at a first point along its span, the first chord line extending from a trailing edge to a leading edge of the first lifting element;   a second lifting element having a second chord line at a second point along its span, the second chord line extending from a trailing edge to a leading edge of the second lifting element; and   a slot through which water may flow when in use, the slot having a constant width across more than half of the slot's length, the constant width extending between the trailing edge of the second lifting element and the nearest point on the first lifting element, and   wherein the first and the second chord lines are non-parallel so as to form a first angle therebetween.   
     
     
         2 . The blade according to  claim 1  wherein the first and/or the second lifting element is selected from the group comprising an aerofoil, hydrofoil, or a flat sheet. 
     
     
         3 . The blade according to  claim 1  wherein the first point is midway along the first lifting element's span, and the second point is midway along the second lifting element's span. 
     
     
         4 . The blade according to  claim 1  wherein the slot is defined by a gap between the first lifting element and the second lifting element. 
     
     
         5 . The blade according to  claim 1  wherein the first angle is between −10 and −1 degrees or between 1 and 60 degrees. 
     
     
         6 . The blade according to  claim 1  wherein the first lifting element is positioned so as at least partially to overlap the second lifting element when viewed normally to the first chord line. 
     
     
         7 . The blade according to  claim 1  further comprising a proximal edge and a distal edge opposite the proximal edge, wherein the first and the second lifting elements extend from the proximal edge to the distal edge and are in connection with each other at the proximal edge and/or distal edge. 
     
     
         8 . The blade according to  claim 7  wherein the first and the second lifting elements are only in connection with each other at one of the proximal edge and the distal edge. 
     
     
         9 . The blade according to  claim 7  wherein the second lifting element is connected to the first lifting element at the proximal edge and/or the distal edge via a flange extending from the second lifting element to the first lifting element. 
     
     
         10 . The blade according to  claim 7  wherein the second lifting element is connected to the first lifting element at the proximal edge via an upper peripheral frame. 
     
     
         11 . (canceled) 
     
     
         12 . The blade according to  claim 10  wherein the upper and/or the lower peripheral frame comprises a hydrodynamic fence. 
     
     
         13 . The blade according to  claim 1  wherein the span of the second lifting element is larger than the span of the first lifting element. 
     
     
         14 . The blade according to  claim 1  further comprising:
 a third lifting element having a third chord line at a third point along its span, the third chord line extending from a trailing edge to a leading edge of the third lifting element; and 
 a second slot through which water may flow when in use, the second slot having a constant width across more than half of the second slot's length, the constant width extending between the trailing edge of the third lifting element and the nearest point on the second lifting element, and 
 wherein the second and the third chord lines are non-parallel so as to form a second angle therebetween. 
 
     
     
         15 . (canceled) 
     
     
         16 . (canceled) 
     
     
         17 . The blade according to  claim 14  wherein the second angle is greater than the first angle. 
     
     
         18 . The blade according to  claim 17  wherein the second angle is greater than the first angle by an amount in the range 3 to 20 degrees. 
     
     
         19 . (canceled) 
     
     
         20 . The blade according to  claim 14 , further comprising a proximal edge and a distal edge opposite the proximal edge, wherein the first and the second lifting elements extend from the proximal edge to the distal edge and are in connection with each other at the proximal edge and/or distal edge, and wherein the third lifting element extends from the proximal edge to the distal edge and is in connection with the second lifting element only at the proximal edge and/or distal edge. 
     
     
         21 . (canceled) 
     
     
         22 . The blade according to  claim 20  wherein the third lifting element is connected to the second lifting element at the proximal edge and/or the distal edge via a flange extending from the third lifting element to the second lifting element. 
     
     
         23 .- 25 . (canceled) 
     
     
         26 . An oar comprising a blade and a shaft extending away therefrom, the blade comprising:
 a first lifting element having a first chord line at a first point along its span, the first chord line extending from a trailing edge to a leading edge of the first lifting element;   a second lifting element having a second chord line at a second point along its span, the second chord line extending from a trailing edge to a leading edge of the second lifting element; and   a slot through which water may flow when in use, the slot having a constant width across more than half of the slot's length, the constant width extending between the trailing edge of the second lifting element and the nearest point on the first lifting element, and   
       wherein the first and the second chord lines are non-parallel so as to form a first angle therebetween. 
     
     
         27 . (canceled) 
     
     
         28 . (canceled) 
     
     
         29 . The oar according to  claim 26  wherein the second lifting element is further away from the shaft than the first lifting element. 
     
     
         30 . (canceled) 
     
     
         31 . The blade according to  claim 7  wherein the first and second lifting elements are in connection with each other only at the proximal edge and/or distal edge.