Freeboard Calculator

Type A vessels (tankers and similarly built ships) typically have better subdivision and damage stability characteristics than general cargo Type B vessels, so the International Convention on Load Lines, 1966 -- carried into U.S. regulation at 46 CFR §42.20-5 -- assigns them freeboard from a lower table than Type B vessels for a given length. This calculator reflects that by applying a smaller freeboard factor (0.025 x length) to Type A versus a larger one (0.035 x length) to Type B, meaning the same vessel length produces a lower minimum-freeboard requirement when Type A is selected.

A negative margin means the actual freeboard (depth minus loaded draft) is below this calculator's estimated minimum freeboard requirement for the vessel's length and type -- the vessel is loaded deeper than the minimum load line standard allows. In practice this calls for reducing cargo or ballast to raise the vessel in the water until actual freeboard meets or exceeds the minimum.

Increasing loaded draft, with overall depth held fixed, directly reduces actual freeboard (since freeboard = depth minus draft), which in turn lowers reserve buoyancy -- the percentage of overall depth still above the waterline. A deeper-drafted, more heavily loaded vessel therefore has proportionally less watertight hull volume in reserve before the deck edge submerges.

No -- it's a simplified, length-based approximation (a fixed percentage of vessel length depending on Type A or B) intended for quick estimation, not the full International Load Line Convention tabular calculation, which also accounts for factors like block coefficient, sheer, and superstructure. An official load line assignment and freeboard marking requires review by a naval architect or classification society against the actual convention tables.