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Ship handling involves the way a ship moves and the factors that affect its movements.
- Center of Mass (center of gravity). The imaginary point in a ship that is the center of the mass of the ship. It is the point about which the mass rotates.
- Pivot Point. The fore and aft location about which the ship pivots when her rudder is put over or when steering with engines. With the ship dead in the water, the ship pivots about a point 30 percent of the distance from the bow to the stern. When underway and proceeding ahead, the pivot point is abaft the bow about 15 to 20 percent of the length of the ship. The location of the pivot point must be considered in turning into and out of the wind.
- Axes. A ship moves in three-dimensions about its center of mass and along its 3-axes:
- Longitudinal Axis. An axis drawn through the center of the vessel from stern to bow, through the vessel’s center of mass, parallel to the waterline.
- Vertical Axis. An axis drawn vertically, through the vessel’s center of mass, perpendicular to the longitudinal axis, parallel to the waterline.
- Horizontal (lateral, transverse) Axis. An axis drawn from horizontally, through the vessel’s center of mass, perpendicular to the longitudinal axis, parallel to the waterline.
- Linear Motions
- Heave. The up and down motion along the vertical axis.
- Sway. The lateral (side-to-side) motion along the horizontal axis.
- Surge. The forward and backward motion along the longitudinal axis. The distance gained or lost while changing speed.
- Rotational Motions
- Pitch. Rotation about the horizontal axis. The bow and stern move up and down in opposite directions.
- Roll. Rotation about the longitudinal axis. The sides move up and down in opposite directions.
- Yaw. Rotation about the vertical axis. The bow and stern move side to side in opposite directions.
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