http://files.dnr.state.mn.us/educati...atbuilders.pdf
coast guard regs. for boat builders . . . I believe guidlines are the same for real boat builders. A 2000lb fiberglass boat under water doesn't require 2000lbs of foam floatation to float. see pages 16 - 29.
BASIC FLOTATION. Builders of inboards and inboard-outdrives are required to
comply with the Basic Flotation portion of the Coast Guard Flotation Standard. Basic
Flotation requires a fully loaded boat to float with some portion of the boat above the
surface of the water when it is swamped. This means that the boat must contain
sufficient flotation to support two-fifteenths (2/15) of the persons capacity and 25
percent of the dead weight. Basic Flotation is designed to give the survivors of a
boating accident in which the boat has swamped something on the hull to hang onto.
The advantages of Level Flotation versus Basic Flotation are obvious (see introductory
paragraphs to Level Flotation section).
Builders of boats that are subject to the Basic Flotation requirements should perform
Steps I and II in the “Calculations section on the following pages and substitute 25
percent of their boats’ rated maximum weight capacity for Step III in the appropriate
example. Also, since Basic Flotation requires only that some portion of the boat
remain above the surface of the water, the location for the required amount of flotation
material is unimportant.