ON A WAVE PROPELLED VESSEL. 87 



" power may be abstracted from the swell of the ocean by means 

 "of the trochoided plane, thus : — Take aflat float and rigidly con- 

 " nect a plane at some distance below parallel to the float, and it 

 "will be found that the plane and float alternately pull each other 

 " in the direction of propagation of the waves, the result being that 

 " the apparatus progresses through the water faster than a float 

 " without the plane attached. If the plane is fixed vertically at 

 " right angles with the float, the resultant is in a direction con- 

 " trary to that in which the waves are moving."* 



This model will be seen from the drawing (Plate xn.) to be 

 a punt-like structure, ballasted with lead to a draft equal to half 

 the depth. The displacement is about five pounds. 



Under the fore-foot is a clamp for securing a boomf that carries 

 at its extremity a thing like a balanced rudder with the post 

 horizontal. This is called the plane-propeller. A piece of wire 

 projecting horizontally aft from the boom-end serves as a stop. 

 The plane-propeller is free to move on its axis either way, until 

 it is stopped by a piece of string and india-rubber connecting the 

 stop and the propeller blade. 



The axis of the plane-propeller is about half the model's length 

 in advance of the stem, and at a sufficient depth to be always 

 immersed. 



There is a vertical axis to the bearings of the plane-propeller, 

 so that the stop and propeller can be rotated horizontally. This 

 enables the model to turn circles or go with the wind and sea aft. 

 As the model rises and falls with the sea, the plane-propeller 

 acting in less disturbed water, makes a resultant greater than the 

 wind friction plus the skin resistance. 



* Photographs of these two models will be found in " The Evolution 

 of the Flying-machine " in the Library of the Royal Society of N'.S. Wales. 



f It will be obvious that in practice the boom will not project, as in 

 this experimental model, from the forefoot. The vessels will be of great 

 beam, with long overhanging bows, at the extreme end of which the pro- 

 peller will be situated. (Plate xiii.) 



