OOW Prep
Module 15 · Interactive

Stability Visualiser

Watch GM change in real time as you consume fuel, introduce free surface, and fill a high ballast tank. The cross-section shows K, B, G, M live — and the GZ curve redraws instantly. Push all three controls to their extremes and see the vessel loll.

What you're practising

How fuel consumption, free surface effect, and high ballast each move KG — and why the combined effect can produce negative GM and loll.

Pass criterion

Explain GM = KM − KG, the free surface correction formula, and what happens to the GZ curve when GM goes negative. Identify loll on sight.

Full tanks0%Empty

Removes 0t from double bottom (KG 0.5m) → G rises

i_t = 100 m⁴ — toggle to activate

Empty0%Full

Adds 0t at KG 6m — raises G further

KG

3.10 m

KM

4.20 m

GM

+1.10 m

Adequate
KkeelBcentre of buoyancyKB 1.8mGcentre of gravityMmetacentreBM 2.4mGM +1.10mwaterline
Cross-section — K, B, G, M update live as you move the sliders

GZ curve — righting lever vs angle of heel

Green = positive righting · Red = loll · Initial slope = GM

Module 15 — Study Notes

Full written notes covering GM, righting lever, free surface effect, freeboard, watertight integrity, and heavy weather preparation.

Open Module 15 notes →