The trimming moment in tonne-metres needed to alter a vessel's trim by one centimetre, used in stability calculations.
In practice
In practice, the chief mate applies MCT1cm to determine what weight must be shifted—or what trim moment must be created—to achieve the required departure trim. Trim by the stern is generally preferred for sea passage to improve propeller immersion and steering, while trim by the head may be needed to float the vessel off a berth with limited aft water depth. Bending moment calculations in the loading instrument also use MCT1cm implicitly. A good understanding of MCT1cm enables the chief mate to quickly estimate the consequences of any weight change on the vessel's trim before entering it into the loading computer.
Regulatory detail & full definition
The Moment to Change Trim one centimetre (MCT1cm or MCTC) is the trimming moment in tonne-metres required to change a vessel's trim by one centimetre without altering the mean draught. It is a function of the ship's waterplane area, underwater hull form, and the distance between the centre of buoyancy and the metacentre for trim (BML). MCT1cm is tabulated in the hydrostatic tables of the ship's stability booklet at each mean draught and is used by the chief mate to calculate the trim change resulting from loading, discharging, or transferring cargo, ballast, or fuel between tanks.
In practice, the chief mate applies MCT1cm to determine what weight must be shifted—or what trim moment must be created—to achieve the required departure trim. Trim by the stern is generally preferred for sea passage to improve propeller immersion and steering, while trim by the head may be needed to float the vessel off a berth with limited aft water depth. Bending moment calculations in the loading instrument also use MCT1cm implicitly. A good understanding of MCT1cm enables the chief mate to quickly estimate the consequences of any weight change on the vessel's trim before entering it into the loading computer.