Ship Stability API

Ship initial-stability maths as an API, computed locally and deterministically — the metacentric-height, righting-moment and rolling-period numbers a naval architect, ship officer or marine-surveyor judges a vessel by. The metacentric-height endpoint gives GM = KM − KG, the single most important stability figure: the height of the metacentre (set by the hull form and draught) above the centre of gravity (set by how the ship is loaded), with a classification from a dangerous negative GM, through tender and comfortable, to a stiff GM that rolls violently — naval architects aim for the middle, because too little is unsafe and too much is hard on cargo and crew. The righting-moment endpoint gives the small-angle righting arm GZ ≈ GM · sin(heel) and the righting moment (GZ × displacement) that pushes the ship back upright, valid up to roughly 7–10° before the true GZ curve bends away. The roll-period endpoint gives the natural transverse rolling period T = 2π·k / √(g·GM) from the GM and beam — the same relation sailors run in reverse as the rolling-period test, where a suddenly longer roll warns that GM has dropped. Everything is computed locally and deterministically, so it is instant and private. Ideal for naval-architecture and ship-design tools, marine-surveyor and loading-software utilities, maritime-training apps and stability dashboards. Pure local computation — no key, no third-party service, instant. Initial-stability estimates — use full KN cross-curves for large angles. 3 compute endpoints. For hull speed and design ratios use a sailing API.