Safe Loading — Subpart C

Calculation of Maximum Displacement

The most practical methods used to calculate displacement are:

CAD System (Computer Aided Design): If CAD software is available and the hull lines are in the computer, it is easy to establish the float-plane and figure the volume below this plane. Any program with hydrostatic capabilities can compute this.

Boat Immersion: Although this method requires some infrastructure, such as a pool, an overhead crane or other lifting system, plenty of weights, and labor, it is the method followed by professionals who do this work under contract for others.

The system, as its name implies, consists of placing the boat in a tank or pool while it is suspended level from above by a pair of hoists that permit lowering it into the water, and then adding weights distributed evenly so the boat immerses with the float-plane parallel to the surface of the water. All points of minor leaks are sealed, such as deck-to-hull joints, bilge pump discharges, other scuppers or drains, and a three inch hole in the engine well as described in CFR 183.35 (b) (1) in the case of an outboard. When the water begins to come into the boat, which is at the lowest point of immersion, the weights are computed and give us the maximum displacement.

It is important to understand that the maximum displacement is the weight added to immerse the boat to its static float-plane, plus the weight of the boat, propulsion machinery and full fuel tank. This method is a hands-on procedure as opposed to a calculated one. When the boat is placed in the water, its weight already displaces water and consequently this weight must be added to the weights being placed on the boat in order to submerge it to the static float-plane.

All other methods shall consider the weights of the boat and machinery as the formulae indicate in sections 5.0, 6.0 and 7.0.

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