STEAM NAVIGATION. 



56. To remove this defect, and economise as much as possible the 

 propelling effect of the paddle-boards, it would be necessary so to 

 construct them that they may enter and leave the water edgeways, 



Fig. 13. 



or as nearly so as possible ; such an arrangement would be, in 

 effect, equivalent to the process called feathering, as applied to 

 oars. Any mechanism which would perfectly accomplish this 

 would cause the paddles to work in almost perfect silence, and 

 would very nearly remove the inconvenient and injurious vibration 

 which is produced by the action of the common paddles. But the 

 construction of feathering paddles is attended with great difficulty, 

 under the peculiar circumstances in which such wheels work. 

 Any mechanism so complex that it could not be easily repaired 

 when deranged, with such engineering implements and skill as 

 can be obtained at sea, would be attended with great objections. 



Feathering paddle-boards must necessarily have a motion inde- 

 pendently of the motion of the wheel, since any fixed position which 

 could be given to them, though it might be most favourable to 

 their action in one position, would not be so in their whole course 

 throiigh the water. Thus the paddle-board when at the lowest 

 point should be in a vertical position, or so placed that its plane, 

 if continued upwards, would pass through the axis of the wheel. 

 In other positions, however, as it passes through the water, it 

 should present its upper edge, not towards the axle of the wheel, 

 but towards a point above the highest point of the wheel. The 

 precise point to which the edge of the paddle-board should be di- 

 rected is capable of mathematical determination. But it will vary 

 according to circumstances, which depend on the motion of the 

 vessel. The progressive motion of the vessel, independently of 

 the wind or current, must obviously be slower than the motion of 

 the paddle-boards round the axle of the wheel ; since it is by the 

 difference of these velocities that the re-action of the water is pro- 

 duced, by which the vessel is propelled. The proportion, however , 

 between the progressive speed of the vessel and the rotative speed 

 of the paddle-boards is not fixed ; it will vary with the shape and 

 152 



