Page:Popular Science Monthly Volume 88.djvu/476

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��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.

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