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Geometric Entities

Dimensions

1. Length: It is defined as the distance between the bow and stern of the ship (front to back, measured in a straight line).
2. Beam: It is defined as the distance between the port side to the starboard ship measured at the mid ship. It is the width of the boat at it’s widest point.
3. Depth: It is defined as the distance between the underside of the deck to the bottom the hull.
4. Forward Direction: The axis direction along which the ship moves.
5. Up Direction: The axis perpendicular to the forward direction pointing upward from the water surface.

 

Figure 8.5 - Vessel Dimensions1Source: http://www.brighthubengineering.com

Figure 8.6 - Center of gravity and buoyancy2Source: http://www.otenmaritime.com

Physical Properties

1. Mass: Mass of the vessel.
2. Moment of inertia: The moment of inertia of the ship about the longitudinal axis (pitch direction)
3. Center of Gravity: The point through which the entire weight of the ship is acting vertically downwards.
4. Center of Buoyancy: The point through which the entire buoyancy force(opposing the weight)of the ship is acting vertically upwards.

The relative positions of the center of gravity and the center of buoyancy will determine the stability of the vessel.