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Freeboard is the vertical distance from the waterline to the freeboard deck: moulded depth minus draft. It is the measure of reserve buoyancy, the watertight volume above water that keeps the ship afloat when it heels or takes water on deck, which is why load line rules assign a minimum value.
Freeboard
Freeboard = moulded depth - loaded draft; reserve buoyancy ratio = freeboard / draft
Marine results are planning estimates only. Verify against the vessel's approved stability booklet, loading manual, class society rules and applicable maritime regulations before loading or sailing.
Because reserve buoyancy determines survivability in heavy weather and after damage. The Load Line Convention assigns freeboard from length, type and superstructure.
Each mark is the maximum draft for a zone and season — tropical, summer, winter and fresh water — reflecting different sea conditions and water densities.