Polytechnic Association Proceebings. 357 



strength and safety 

 Are an essential feature in any propeller. In this we claim supe- 

 riority. First: in the employment of steel in its construction, which 

 is six times as strong as cast iron. 



In the paddle wheel and screw the strain is multiplied by lever- 

 age, or momentum and concussion; while in this propeller the 

 parts are so peculiarly arranged that they are subjected only to 

 direct tension and compression, with no leverage or shocks of any 

 kind. We not only have a stronger material for its coustruction 

 but have from one hundred to three hundred per cent less strain 

 upon the parts. 



Second: we have four chances instead of one in case any acci- 

 dent happens to the steering aparatus. If the rudder is disabled, 

 the boat is uncontrollable. Bat if one of the blades of this pro- 

 peller is disabled, there are three left. If two are disabled we have 

 two remaining. And if we have but one we can control our boat 

 and keep on our course, as each blade is independent of the other. 



The blades being in a vertical position there is no lashing the 

 sea and straining the boat as the stern rises and falls in a seway; 

 and in case of leakage at the shaft, the boat will not sink as the 

 apparatus through which the shaft passes into the boat is above the 

 water line. 



The wheel is in a less exposed situation, not coming so near the 

 surface of the water nor extending to such a depth into the water 

 as the screw, though of the same propelling powers. For this rea- 

 son it is more securely below ice and other obstructions floating on 

 the surface of the water; and not so likely to come in contact with 

 rocks or objects upon the bottom of shoal waters as the screw. 

 True it has more lateral extension than the screw, but this is the 

 direction in which there is the most room and least exposure. 



SIMPLICITY OF MACHINERY 



Is a marged feature, when it is taken into account the number of 

 results produced. Let us suppose that the screw is so arranged 

 that it can turn in its own length of water, and back without any 

 liability of sticking its engines on their centers. To do that it will 

 require two propellers and two double engines. How does a com- 

 parison with this stand ? For one wheel on this you will have two 

 wheels on the screw. For one cylinder on this you will have four 

 cylinders on the screw. For two eccentrics on this you will have 

 only eight eccentrics on the screw. And for the absence of any 



