A Safe-Load Rule for Dugout Canoes: Freeboard, Metacentric Height and the Cost of Standing Up

A dugout canoe is usually loaded by eye: fish, gear and people are added until the boat feels low or tender, and the judgement is made afloat, when changing it is hardest. This paper replaces that judgement, for planning purposes, with a computed rule. A simple hydrostatic model of a dugout hull — displacement from a block coefficient, freeboard from hull depth minus draft, and transverse stability from the metacentric height — is applied to four canoe sizes, and the largest payload is found at which two stated limits both hold: a minimum freeboard of 0.15 m and a minimum metacentric height of 0.15 m. In every size the stability limit is reached long before the freeboard limit. For the reference canoe of 5.0 m length, 0.85 m beam and 0.45 m depth, the safe payload with everyone seated is 300 kg, while the freeboard alone would allow 588 kg; loading to the freeboard figure would leave the metacentric height negative in the standing case and at the stated minimum in the seated case. When the payload is treated as standing, the safe payload of the same canoe falls to 151 kg, a reduction of 149 kg or 49.7 percent. Across the four sizes the reduction on standing ranges from 47.5 percent to 55.9 percent. The practical rule is therefore twofold: load a dugout by its stability figure, not by the space or freeboard that remains, and treat standing up in a loaded canoe as roughly halving the load the canoe can safely carry. The study is simulated, not measured.