Displacement of a Deflected Ship Hull

This note summarizes relevant approximations based on permanent waterplane characteristics for a more accurate assessment of the effects of longitudinal deflections of an elastic ship's hull on drafts and displacement during marine surveys of merchant ships. The possibility of a different practice for placement of draft marks alongside a ship, ensuring the same precision in displacement assessment of a deflected and trimmed hull by only two draft observations, is investigated by employing the waterplane properties. Correction factors for conventional ships, based on waterline coefficient for changes of hydrostatic load, arising due to hull deflections, are also summarized. The results are demonstrated on a bulk-carrier built in Croatia as an example.