In article ,
"Eisboch" wrote:

"Short Wave Sportfishing" wrote in message
...
On Tue, 19 Aug 2008 06:17:37 GMT, Buzzihd Beah
wrote:

Gentlemen,

Say I want to make sure my boat does not sink even if it's full of
water.

It weighs 4330 pounds. Does that mean I have to add about two cubic
meters of foam somewhere? There isn't enough space for that much.

Or can I somehow take into account the buoyancies of fiberglass, fuel
tank, engine, and all the other stuff? Is there a method to calculate
things like that?

Yep - ABYC H-5 (Capacity) and ABYC H-8 (Swamped Bouyancy).

What you want is ABYC H-8.

H-8.7.2 Calculations - Basic Flotation
H-8.7.2.1 Perform the following steps to calculate the volume of
flotation material required to support the swamped boat (Fb), the
submerged propulsion equipment (Fp), the persons capacity (Fc1), and
the dead weight (Fc2).
H-8.7.2.1.1 Step 1: Determine the flotation needed to support the
swamped boat (Fb).
Formula: Fb = (Wh x K1 + Wd x K2 + .69 We) ÷ B
Where
Wh = dry weight of hull, i.e., everything below swamped water line
Wd = dry weight of deck and superstructure
We = dry weight of factory installed equipment, hardware, and
accessories
K1 and K2 = conversion factors for materials
B = buoyancy of flotation material in pounds per cubic foot


EXAMPLE
Calculate the flotation material needed to support the swamped boat
(Fb).
Assume
Wh = weight of hull (fiberglass) = 600 lbs.
Wd = weight of deck and superstructure (plywood) = 120 lbs.
We = weight of equipment, hardware and accessories = 50 lbs.
Fb = ((Wh x K1) + (Wd x K2) + (0.69 x 50)) ÷ B
Fb =((600x0.33)+ (120x-0.81) + 0.69x50)) ÷ 60.4*
Fb = (198 - 97.2 + 34.5) ÷ 60.4
Fb = 135.3 ÷ 60.4
Fb = 2.24 cu. ft.

However, depending on how old your boat is (and/or how big) CG
regulations require level floatation.


That reminds me of when I was a kid living on a small lake during the
summer. We had an old, leaky, canvas covered canoe with a small deck
section at each end. A friend of my father brought some liquid stuff over
in two bottles one Saturday that he had "confiscated" from work.

They poured some liquid from each bottle in the void under each deck section
and we watched as they reacted and "grew" into huge mushrooms of foam. They
used a little too much and spent an hour or so with a hacksaw blade cutting
most of it out to make room for passengers.

A good modern expanding foam would crack that canoe