Thanks for that link. Excellent resource! =D> Very technical, but a little basic math can help determine whether you've got enough foam.
They give an example, although, they give it for a fiberglass boat. That doesn't help those of us with aluminum boats. We need an example for that. So, if y'all don't mind me posting this.....here ya go:
Here's what I came up with for my jetboat, which is a modified 1648 Duracraft.
DISCLAIMER: This is a rough guess-timate, your particular application may be different, but this should at least give everyone an idea:
Step 1: Determine the flotation needed to support the submerged boat (Fb).
Fb =([Wh x K] + [Wd x K]+ .69We ) ÷ B
Fb = flotation needed
Wh = dry weight of hull (425 lbs for Duracraft 1648)
Wd = dry weight of deck and superstructure (75 lbs for flooring, rear deck)
We = dry weight of factory installed equipment, hardware and accessories (50 lbs for console, cables and wires)
K = conversion factor for material used. See Table 4.1 below
B = buoyancy of one cubic foot of flotation material expressed in pounds.
Since the total weight for aluminum is multiplied by .33.....I added up the weight of everything, did the conversion, and arrived at (284 lbs)
Step 2: Determine the flotation material needed to support the submerged propulsion equipment (Fp).
Fp = G ÷ B
G = 75% of the installed weight of the engine, drive and battery (inboard), or the engine, outdrive and battery (sterndrive) - in pounds to the nearest whole number;
(320 lbs total...this accounts for 75% of the weight of the engine, battery, and jet pump)
Step 3: Determine the flotation material needed to support the persons capacity (Fc).
Fc = .25 (C) ÷ B
C = Maximum weight capacity. ( 3 persons @ 150 lbs or 450 total)
B = Buoyancy of 1 cu.ft. of flotation material used in pounds.
(112 lbs total)
Step 4: Determine the total flotation material needed (F) to support the boat. This is the sum of steps 1, 2, and 3 above.
F = Fb + Fp + Fc
So, I added up the 112 lbs for persons, 320 lbs for the engine, and the 284 lbs for the hull, etc...and then divided that total number by 60 (buoyancy of foam per cubic foot) and arrived at a figure of 11.933...that's the amount of cubic feet of foam required....roughly.
Then, knowing that a 4x8 sheet of 1.5" foamboard is about 3.9 cubic feet, and that my floor is about 4x8, along with the 2 gunwales at roughly 2x8', (totalling up for another 4x8' sheet), that's 2 sheets of foam, or roughly 7.8 cubic feet.
I have another cubic foot of foam in the stern, and then about 2-3 more cubic feet in the bow...for a rough estimate of somewhere between 11 and 12 cubic feet of foam all together.
So, I have the minimal amount required, but at least now after doing the math and figuring it out, I feel a lot better about that boat's seaworthiness!
Again, thanks for posting that link, definitely clarifies everything.