Stability
How a ship floats and stays upright: GM, free surface and loading.
Topics in study order
- 1.Flotation, Centres and Metacentric Height
Why a ship floats (density, Archimedes, the law of flotation, draught), the four points of stability K, B, G and M, and how GM = KM − KG tells you if she is stable, neutral or unstable. Every stability question at sea and in the MCA oral starts here.
12 cards
1 Nov 2026 - 2.Good and Poor Stability: Stiff, Tender and the Warning Signs
What good and poor stability look like at sea: stiff and tender vessels, what GM and GZ tell you, the warning signs of a ship losing stability, and how raising weights, low freeboard, blocked freeing ports and slack tanks reduce it. A standard question in the MCA OOW oral.
9 cards
1 Nov 2026 - 3.The GZ Curve and Intact Stability Criteria
How to read the GZ curve (righting lever against angle of heel), what an angle of loll is, and the intact and damage stability criteria of the REG Yacht Code and the 2008 IS Code. Examiners expect you to sketch the curve, name its features and quote the minimum figures.
11 cards
1 Nov 2026 - 4.Free Surface Effect
How liquid moving in slack tanks, flooded spaces or water on deck acts as a virtual rise of G and cuts GM, what makes the effect bigger or smaller, and how to reduce it on board. A standard MCA oral question and a factor in many capsizes.
8 cards
1 Nov 2026 - 5.List, Loll and Heel
The three ways a ship can lean: a list (G off the centreline, positive GM), a loll (G above M, negative GM) and a heel (a temporary tilt from wind, waves or turning). How to tell them apart on board and how to correct each one safely. Mistaking loll for list can capsize a ship, and examiners always ask.
8 cards
1 Nov 2026 - 6.Stability Booklet and Inclining Experiment
What the approved stability information booklet contains, which vessels must carry one, and how the inclining experiment finds the lightship weight, KG and LCG that every loading calculation starts from. A classic MCA oral question for yacht and workboat masters.
10 cards
1 Nov 2026 - 7.Dry-Docking and the Critical Instant
How a vessel loses stability as she settles on the keel blocks: the upthrust P, the critical period and critical instant, and the virtual loss of GM. How to prepare for docking and undocking, with and without damage. A classic MCA Master oral and stability question.
11 cards
1 Nov 2026