“This pamphlet shows how to calculate your boat’s safe horsepower capacity (if it will
be powered by an outboard) and its safe load capacity (both in pounds and the
numbers of people). This pamphlet also explains how to determine how much flotation
material you need to keep your boat afloat if it is swamped, and where to install the
flotation.”
http://files.dnr.state.mn.us/education_safety/safety/boatwater/backyardboatbuilders.pdf
relevance for canoes/kayaks?
While containing some important info for powerboats and large sailboats, there is little useful information contained within for home built canoes or kayaks.
Dave
For a kayak, the safe capacity
in persons is usually equal to the number of cockpits. I’m not sure why a motor-oriented site would be of help regarding the pound capacity of a canoe. Canoe makers often lie about this by using the 6" freeboard capacity. But knock about 40% off that figure and you’ve got a safe estimate of load capacity.
I have used this method to check
the volume of homemade canoes. A board clamped accross the rails with a level taped on top and a ruler taped down the side allows accurate detection of 6 inch freeboard. The 17’ canoe I built held about 625 pounds of water to the 6 inch freeboard line. I estimate the top 6 inches might have held 800 pounds. In use that boat is good for about 500 pounds comfortably. I suspect the Coasties may be in the ballpark for canoes as well as motor boats.