Quote:
For a 17' outboard they say 20 cubic feet (or about 5 gallons of uncured foam). For a 20' inboard, they say 22 cubic feet. P. 26 suggests pouring foam down the gunnels.
How much floatation should I add? I assume what is in the stringers is enough to pass the restrictions, but how much is enough to float the boat?
Can we convert that to plain english for 20's and 23's?
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Ken - The formula breaks the equation down to 3 steps. Calculate the foam floatation required for Boat (FB) motor (FM) and People (FPC). To keep it simple we'll not use include any floatation added by coring (like transom plywood, balsa deck, etc).
Boat = 1600 x .33 (fiberglass) + weight of gear on deck (200lbs) = 728lbs/60.4 = 12 cu. ft
Motor = 352lbs (suggested submerged weight) includes battery, controls, etc. (75% of dry weight)
=352lbs/60.4 = 5.82 cu. ft
People = Still not 100% sure on this one. maybe someone can explain this.
18cu. ft of foam is enough to float a rigged 20 seacraft without people on board. If you count the transom wood and the balsa/plywood deck quite a bit less than 18 cu. ft. You can take measurements on the stringers . . . but I would guess that 4 stringers full of dry foam (pre-72 hull) would be more than enough to float that hull with the motor and people. The boat might turtle b/c of stability, but won't sink.