448 



Popular Science Mo7ithly 



should be made of steel, and should be 

 riveted in place. On the end of the 

 brass tube is mounted the steering wheel. 

 A good idea of the complete device can 

 be gained from Fig. 5. 



The two rear runners should now be 

 bolted to the body of the craft with i/4'' 

 bolts. These runners should overlap the 

 rear of the body by 3", leaving about 11'' 

 of surface to bear against the body. The 

 bottom edges of the runners should be 

 3'' below the body. In other words the 

 clearance of the body at the rear should 

 be 3". At least 3 bolts should be put 

 through each runner. 



Figure 6 gives a good view of the 

 brake. This is constructed of two pieces 

 of iron, or soft steel. One piece 30" 

 long by V2'' in diameter has its extremi- 

 ties bent at right angles making legs 4" 

 long. These are flattened as shown, and 

 saw teeth filed to engage with the ice. 

 To one of these legs is affixed the 1" 

 X ^/4" iron lever by means of rivets. This 

 is brought to the bottom of the leg and 

 afifords additional surface to engage with. 

 The upper end of this is rounded to fit 

 the hand. This brake is attached to the 

 bottom of the body 20" from the rear by 

 means of three stout brass straps. The 

 lever is bent out to clear the side by about 

 3" and when not in use is held against 

 a small block by means of a spring as 

 shown in Fig. 1, so as not to drag on 

 the ice. 



The next step is to select a good sec- 

 ond-hand motorcycle motor of from 3 to 

 4 h.p. A motor in good running condition 

 can be bought for $10.00 with battery 

 ignition, and for about $15.00 with a 

 magneto. This motor is mounted at the 

 extreme rear of the sled, and is held 

 firmly in position by two U-shaped iron 

 supports, one of which is shown in Fig. 

 1. These supports should be about Vi" 

 thick by IV^" wide, and should be high 

 enough to elevate the motor so that the 

 distance between the top rear edge of the 

 body and the main crankshaft bearing is 

 about 18". This will require about 44" 

 of strap iron for each support, as these 

 pieces must extend high enough up on 

 each side of the crankcase to permit of 

 two crankcase bolts on each side being 

 passed through the supports, provided 

 the engine in question has two bolts to a 

 side, which is generally the case. 



The controls on most second-hand mo- 

 tors are so different that it is practically 

 impossible to give any method for rig- 

 ging them up on the motor ice-boat. The 

 simplest method, is to use flexible con- 

 trols for the spark and gas, mounting the 

 levers on the side of the boat near the 

 brake handle, in such a manner that they 

 do not come in the way when actuating 

 the brake. 



The next consideration in equipping 

 the craft is to provide an aerial propeller 

 of the proper diameter and pitch. So 

 many things must be taken into consider- 

 ation in designing a propeller for an ice- 

 boat that it is practically impossible to 

 submit any one design which will work 

 at high efficiency on any motor ice-boat. : 

 In order to obtain the very highest effi- 

 ciency exhaustive experiments with pro- 

 pellers of different dimensions would be 

 necessary. However, for ordinary work 

 an aerial screw having an over-all length 

 of 3' will be found entirely satisfactory, 

 in Fig. 7, a design is submitted which will 

 give good results with a motor of from 

 3 to 4 h. p. The greatest pitch of this 

 propeller is 4'. This means that at every 

 revolution the propeller theoretically ad- 

 vances 4' and in practice somewhat less 

 than 3' if we figure the efficiency at about 

 70 per cent. 



The exact dimensions for the propeller 

 are indicated in the sketch. The cross- 

 sections of the blades given show the 

 size and angle every 3" from the center 

 to the tip. It will be noted that the un- 

 der-surface of the blade is slightly con- 

 cave, most of the cross-sections being 

 semi-streamline in form. This propeller 

 can be constructed of a 2" by 6" spruce 

 plank slightly over 3' long. Spruce is 

 one of the best materials for this pur- 

 pose and also the cheapest. Most of the 

 work in turning out this propeller can be 

 done with a small hatchet or a draw- 

 shave, and finished up with a spoke- 

 shave. The blades should be well sand- 

 papered and given several coats of shel- 

 lac. This propeller is bolted directly to 

 the pulley or sprocket as the case may 

 be, on the end of the motor crankshaft, 

 with two %" bolts, the ends of which 

 should be secured to prevent their loos- 

 ening. 



Tlie machine which has been described 

 will carry two passengers. 



