The boy mechanic, book 3

by Unknown

Unless a motor of extremely light weight is procured, a canoe of frail construction and less than 16 ft. long is not likely to stand the jar of the driving mechanism. The canoe illustrated in the [page plate] is 18 ft. long, of 36-in. beam, and strongly planked, decked, and braced. A canoe of even broader beam would tend to give more stability in rough water, and if it is desired to transport heavy camping packs, or other material, in the craft, this factor should be observed particularly. Likewise, the depth and draft must be considered, as the carrying capacity and seaworthiness of a canoe depend in part on these factors. The fitting of the various parts of the mechanism and accessories must be done with the aim of balancing the load evenly. If properly disposed, the weight of these parts should tend to lower the center of gravity of the canoe, thus rendering it more stable.

The actual work of installing the motor and fittings should be preceded by careful planning and the making of a full-size diagram of the stern portion of the canoe as rebuilt. Too much care cannot be taken in this work, as, if it is neglected, the craft may be rendered unsafe, or the motor and fittings may not operate satisfactorily. The motor should be set in the stern, as shown in the [illustration], as this will permit the use of a minimum of shafting and other fittings which must be accommodated. The exact location of the motor may vary with canoes and engines of different types. This should be tested out by placing the motor in the canoe and noting the effect on its balance in the water. For a canoe of the dimensions indicated, and a light-weight motor, 5 ft. from the stern is a satisfactory position. The motor should be placed as low in the canoe as possible, allowing the flywheel and crank case sufficient clearance below.

A convenient method of operation is as follows: Place the canoe on boxes, or sawhorses, taking care that it is properly supported about 2 ft. from the ground, or floor. Take measurements directly from the canoe, or part to be fitted, whenever convenient. Procure two sheets of paper, 30 in. wide and 7 ft. long; mark one “diagram” and the other “templates,” and use the former for the full-size detail and the other for the making of templates for curved or irregular parts.

Begin the diagram by drawing the base line AB, [Fig. 3]. This is the lower line of the engine bed and the upper surface of the ribs. Draw the line CD perpendicular to the base line, and 18 in. from the left end of the sheet. The point C is the center of the stern end of the driving shaft. The dimensions of parts are not given, except in special instances, since they must be obtained from the particular canoe and other parts entering into the construction. Indicate the layer of ribs E, the planking F, and the keel G. Using the template sheet, cut a template or pattern for the curved stern. This may be readily and accurately done by fixing a straightedge to the keel and permitting it to extend to A. Rest the long edge of the sheet on the straightedge when fitting the template to the curve. Use the template as a guide in marking the curve on the diagram, as at HJ. The curve K, of the stern decking, may be indicated similarly.

Determine the distance the motor is to be set from the stern and indicate it by the perpendicular line L. Measuring from the base line, indicate the height of the center of the motor shaft from the floor, as at M. This should be made as low as possible, permitting sufficient clearance for the flywheel and the crank case. Draw a straight line from C to M, which will thus indicate the center line of the driving shaft. This line is fundamental in determining the dimensions and placing of certain parts and fittings, and should be established with extreme care. The size and exact position of the engine bed N may now be indicated. Its dimensions, given in detail in the perspective sketch, [Fig. 5], are suggestive only. They may be varied in order to provide proper bearing on the floor, and so that the bolts holding the bed may pass through ribs. The cross brace at the forward end is important, and should be fitted carefully over a rib. The upper line of the engine bed must not be confounded with the center line of the shaft, for in many engines they are on a horizontal line when viewed from the forward end, yet not necessarily so. The slant of the engine bed must be made accurately, as any deflection from the angle of the center line of the shaft will disarrange the installation.

The shaft log O may next be indicated and a template made for use in guiding the bit when boring the hole for the shaft through it. The template used for the curve HJ may be altered by drawing the shaft log on it at the proper place. The point P, from which the bit is to be started when the shaft log is fixed into place, should be indicated and the center line of the shaft extended to Q, may then be used as a guide for the bit. If the homemade type of bearing R is used, it should be indicated on the diagram. A metal bearing may be made, or a suitable one obtained from dealers in marine hardware. In the latter case it will probably be necessary to block up the bottom of the canoe in order to provide a flat, horizontal bearing surface for the bearing flange.

The rudder and other parts, which are not directly connected with the motive-power unit, may be indicated in detail on the diagram or be made from sketches of a smaller scale. Paper patterns, made full size, offer a convenient method of outlining the parts of the engine bed, the rudder, and other irregular pieces. When the diagram is complete, measurements may be transferred directly from it without reducing them to figures, and, wherever possible, parts should be fitted to it.

The shaft log, shaft bearing, and engine bed may be made of oak, or other strong hard wood. It will be found desirable to have the engine bed complete before an attempt is made to fit the shaft and its connections. It is made of 1¹⁄₂-in. stock, bolted together with lag screws and fixed firmly into the canoe with bolts. The heads of the bolts should be provided with cotton and red-lead packing, and care should be taken that the bolts pass through ribs.

The shaft log should be fixed into place before it is bored. Bolts may be passed through it and fastened on the inside if there is room for drawing up the nuts in the stern. Large screws may be used to aid in the fastening and smaller screws may be used from the inside. The lower rudder support will also aid in holding the log in place, and the iron straps S, [Fig. 3], will insure its rigidity. This is an important point in the construction, as if the log is not fixed positively, the thrashing of the propeller will soon loosen it.