Why A Fishing Vessel Remains Upright

Another way of understanding how a fishing vessel stays upright is to imagine the rocking of a baby cradle, as shown in the figure. The fishing vessel (weight) is represented by the cradle and its centre of gravity (G) is the near the centre of the cradle. The “buoyant force” supporting the cradle is represented by the rocker resting on the floor and the centre of buoyancy (B) is the point where rocker contacts the floor.

As with a fishing vessel, the cradle’s (vessel’s) centre of gravity (G) is above its rocker, the centre of buoyancy (B).

The slightest disturbance (wind or waves) causes the cradle (vessel) to roll (heel) to one side. As the cradle (vessel) rolls to one side, the point where the rocker touches the floor (the centre of buoyancy (B)) shifts outboard. To keep the cradle (vessel) upright, the point where the rocker touches the floor (the centre of buoyancy (B)) must shift outboard.

It is this shifting of the centre of buoyancy (B) that allows a fishing vessel to return to upright after being heeled by an external force.

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Metacenter

Vertical lines drawn from the centre f buoyancy at consecutive small angles of heel will intersect at a point called the metacentre (M). The metacentre can be considered as being similar to a pivot point when a vessel is inclined at small angles of heel.
The height of the metacentre is measured from the reference point (K) and is, therefore, called KM.

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