Metacentric Height (GM)
Metacentric height (GM) is the distance between a ship's centre of gravity (G) and its metacentre (M), calculated as KM minus KG. A positive GM means the vessel tends to return upright after heeling. The general criteria of the IMO Intact Stability Code require an initial GM of at least 0.15 m, but each ship has its own limits in its stability booklet. Too little GM makes a ship tender; too much makes it stiff, with violent rolling that raises loads on deck lashings.
Related terms
- Centre of Gravity (CoG)
The centre of gravity is the point where the whole weight of a load can be considered to act.
- Stowage Plan
A stowage plan is the planned position of every container or cargo unit on board a vessel, built by line and terminal planners before the ship berths.
- Lashing
Lashing means securing cargo so it cannot shift under the accelerations of a sea voyage or a road journey.
- Draft (Draught)
Draft, or draught, is the vertical distance from the waterline to the keel, read from draft marks at the bow, midships and stern.
Covered in these guides
Onboard Loading Computer vs Shore-Side Planning: Class Approval and Reconciliation
What a class-approved loading instrument is (IACS UR L5, Rec. 48), type vs ship-specific approval, and how to reconcile shore-side stowage plans with it.
5 min read Vessel stowageVGM in Vessel Stowage Planning: Discrepancy Thresholds, Hold Status and VERMAS
How planners use SOLAS VI/2 VGM in the stowage plan, VGM vs booking weight thresholds, the no VGM no load Hold status, VERMAS EDI and the effect on stability.
6 min read Vessel stowageMetacentric Height (GM) Explained: Calculation, Corrections and Limits
A deeper look at a ship's GM, from hydrostatic KM, loading KG and free surface correction to worked examples and the risks of too little or too much GM.
6 min read Maritime professionalsWhat Is a Stowage Plan? Meaning, Who Makes It, Inputs and Constraints
What a container ship stowage plan is, who prepares it, inputs such as VGM, DG and reefers, stability and lashing constraints, and how it differs from a load plan.
5 min read