A 21' Low-Powered V-Bottom Runabout
By William Atkin
A Speedy and Comfortable 21-Foot V-Bottom Runabout Designed for Modest Power
The plans of Slipby show a handsome little boat of a very practical and useful type; and one that will be fast considering the modest power installed. Stepby is 21 feet in overall length; 20 feet on the water line; 5 feet in breadth; and 1 foot 1 1/2 inches in draft. The hull is of V-bottom form and all the sections are straight, making an easy boat to build.

I must point out that Slipby, as her name suggests, is designed to go through the water easily, rather than over it. Consequently she will be especially comfortable in rough water and a very good sea boat in the bargain. One can over-do the feature of narrowness in a motor boat but if the breadth is kept to about one fourth of the water line length and without excessive freeboard and height, an excellent model will result and one that will travel well with very little horsepower.

The two seats make comfortable room for four. Steering is done with tiller lines running, all around the inside of the cockpit having two blocks forward and two aft as shown. There is no objection to fitting standard steering wheel or side lever, if these are desired. I had in mind keeping the boat as simple and practical as possible.

The motor is installed under a house amidships, having hatches for access. The advantage of the house all the way across the boat is that it provides space for oil tins, tools and athwartships room for the exhaust which is always a problem in a little open boat. I would be disposed to run the exhaust through the side of the boat with wafer-cooled muffler to dampen down the noise. However this is a preference and extending the exhaust pipe to the stern will do no harm. The motor shown in the plans is a 5.5 h.p. Lauson. This has a bore and stroke of 3 inches by 3 1/4 inches; cylinder displacement, approximately 23 cubic inches; and develops its power turning 2,100 r.p.m. The weight of the motor with one-way clutch is 184 pounds. This is a water-cooled motor and designed for marine service. At 2,100 turns a minute the speed of Slipby should be close to 11 3/4 miles an hour. And this is nice speed for a low powered boat. The little boat should do up to 15 miles an hour with a motor of 10 to 15 h.p. providing the weight is within reason, say about 325 pounds with its equipment.

Rather than use a strut and have the shaft and propeller exposed to damage when aground, Slipby has a long keel and deadwood. While this adds to the surface resistance and results in a slight reduction in speed, the loss is more than compensated for by the strength and protection the keel gives the boat and its appendages. Also the long keel keeps the boat on a straighter course in rough water. When grounded or out of water the boat can be moved on rollers or skids without the necessity of a special cradle, thanks to the straight strong keel. It will be noticed from the plans that the keel is cut up abaft station 10 leaving just enough propeller post to hold the stuffing box. This permits excellent flow of water into the propeller and protects the shaft and rudder from striking if the boat is pulled up on the beach.
Plans for Slipby are $100




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