Flotation Foam Calculator

Buoyancy credits every material its displaced volume: fiberglass laminate at ~96 lb/ft³ displaces 64 of those pounds in seawater, leaving ~33% effective. Wood is better than free (it lifts), aluminum keeps ~60%, and lead keeps ~94%. The submerged ledger is why two boats of equal dry weight need wildly different foam — the metal-heavy one is the hard case.

The US standard (33 CFR 183, most monohull outboard boats under 20 ft): swamped, the boat must float LEVEL — supporting its gear and the rated crew weight distributed as clinging survivors — not just bob bow-up somewhere. It dictates foam placement (high and outboard, plus under-sole), not merely quantity: the same cubic feet low amidships passes basic flotation but fails level. Builders certify it by swamp test.

Closed-cell only: 2-lb polyurethane (poured) and PE/PVC sheet hold their lift; open-cell upholstery foam is a sponge wearing a costume. The fine print is longevity — even closed-cell pour foam absorbs water over decades through skin damage and saturation, which is the classic story of the old whaler that floats low and weighs double. Restoration rule: soggy foam is replaced foam, weighed against this tool's fresh requirement.

Mostly no — past ~20 ft the volumes become absurd (this tool scales linearly with weight; a 8,000-lb cruiser would want 60+ ft³ for the hardware alone) and the safety architecture changes: compartmentation, bilge systems, self-bailing decks and liferafts replace the float-when-swamped philosophy. Foam survives aboard bigger boats in specific roles: sealed flotation chambers in RIBs and some cats, and impact zones.