Auto-Top Size Fisherman's Boat


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  • Pub No.: 5863
$7.95
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by Bruce N. Crandall

LOA 111/2 FT., BEAM 4 ft. 9 in., DRAFT 6 1/2 in., DISPLACEMENT 575 lbs.

An easy-to-build 111/2-foot, medium-high-speed, soft-riding utility, it's specially designed for low-horsepower outboards and features simple, light construction.

This is a general-utility, auto-topsize outboard boat designed for use with the modern economical 5and 6-hp fisherman’s motors. It is a developable-surface, sheet-plywood model, particularly easy for an amateur to build. The construction is simple and light, with relatively few frames, as the boat is soft-riding and not intended for use at high planing speeds, at which it could be subjected to hard pounding. It is light enough to be carried about on an auto-top carrier. An easy-planing and efficient bottom design is necessary to get the most economical operation from small 5- and 6-hp motors. Their gas economy may be quite poor on a hull which they cannot make plane, but they are capable of 30 miles per gallon or even more on a planing hull of the proper size. The type of bottom design used here is efficient and soft-riding at low planing speeds, though less efficient—uses more fuel for the speed, in other words—than many others at higher planing speeds. Compared to other bottom types, it is also quite efficient at semiplaning speeds, which helps make planing easier with small motors. It’s the large planing area and uniform angle of attack that make planing easier and increase efficiency at iow planing speeds. Absence of suction drag at the chines also increases efficiency at semiplaning and low planing speeds. The seating arrangement is designed for most efficient weight distribution at semi-planing and planing speeds up to 18 mph. With 5- and 6— hp motors, good fore-and-aft weight distribution can be attained with only one aboard, sitting in the stern seat steering by the motor handle, provided the fuel tank and all other weights are placed as far forward as possible. About the same weight distribution will result with the driver in the forward seat, steering by a wheel, and all other weights placed far aft. With two people aboard and the same 5- or 6-hp motor, the boat will be in semi-planing condition and therefore will stand more weight forward; thus two can sit in the forward seat with the rest of the weight aft, or one forward and one aft with all other weights far forward. With motors of less than 5 hp, the boat will always be in semi-planing condition, and it will be difficult to get the correct fore-and-aft balance with only one person aboard except by driving from the forward seat with either a steering wheel or an extension handle. With motors of about 8 hp, the boat will plane with two people aboard, and a steering wheel becomes necessary for safe operation. This is an ideal small fishing boat for most protected waterways, not only because of its exceptional efficiency with 5- and 6-hp motors, but also because it is very seaworthy and safe for its size. The freeboard is higher and the beam much greater than that of the average auto-topsize boat, making for much better stability. This same extra width, especially at the transom, makes for very poor efficiency at speeds below 10 mph, when the hull is in pure displacement condition—-for transom drag is considerable at these speeds. For this reason the hull will not be suitable for rowing any great distance, although it will handle quite well with oars while still-fishing. A hull for best efficiency at rowing speed or with a 1- or 2-hp motor should be very long and narrow, with almost no transom. This same inefficiency at slow speeds, however, especially the transom drag, makes the boat ideal for trolling with a 5- or 6-hp motor, as the transom drag acts much like a trolling plate or large bucket dragged behind and enables the driver to easily secure any trolling speed desired.

8 pages, 5 plate(s)


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