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Glen-L Can-Yak built by Bruce Kiley.

A common question is “how much weight will she hold?” This especially applies to smaller boats such as
canoes or kayaks.

The following will give a rough idea of the displacement of a typical double ended craft such as a kayak or canoe. It will not be accurate with boats that have a transom.

The factors required can usually be measured from the boat or possibly the lines or sections. All measurements must be in feet. These are:

  • D = draft . Estimate draft at the widest point of the boat or approximate midpoint; usually about 3″ – 6″ on the typical canoe / kayak.
  • B = maximum beam at bottom. If round bottom measure width about 3″ above keel.
  • L = waterline length or length chine point to chine point fore and aft measured along the centerline of the boat.
  • Disp. = displacement, weight of everything on board plus boat weight.

To find the displacement at the estimated waterline use the following formula.

.6D x B x L x 62 = Displacement in pounds, fresh water.

Let’s take an example:

We have a kayak that has a draft of 6″ (.5′), a midships bottom width of 20″ (*1.67′), and a waterline length of 17′. Putting these figures in the formula:

.6 x .5 x 1.67 x 17 x 62 = 528 lbs. fresh water displacement.

But let’s say we know the total weight to be carried, boat weight, passengers and gear, in other words
displacement: but how far will the boat sink in the water? Suppose we have a displacement of 450 lbs. Using the kayak example above the formula is altered to solve for draft.

Displacement
—————— = Draft (D)
.6 x B x L x 62

OR

450
———————– = .43′ or 5 1/8″ draft
.6 x 1.67 x 17 x 62

Are the formulas accurate? No, but close enough for estimates. Basically it calculates the underwater volume and converts with a factor (.6) derived from a group of kayaks whose characteristics had been calculated.

Be practical when you consider load carrying ability. Many people, however, are not. They want a small kayak that will carry two full blown adults with lots of gear. Don’t expect to load the boat so there are only a couple of inches of freeboard. Some even want to carry several passengers in a 12′ kayak. Use a
string to simulate the boat outline on the living room floor. Sit the passengers contemplated in the outline and you will readily see if what you desire is practical.

* Convert inches to feet by dividing by 12.

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One Response to Approximating Displacement for Canoes and Kayaks

  1. Peter Edmonds says:

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