Basics of Ship Handling

Ship handling basics for masters and mates.

Ship’s Body and Forces Acting

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High and Low Pressure Area
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Bow and Stern Wave System

Forces Acting on the Manoeuvring Ship

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Longitudinal, Rotational and Lateral Motions

Pivot Point

The Pivot point (PP) is the point around which the ship rotates: when the ship rotates then at this point there is no transverse velocity. The Pivot Point is a kinematic object – it tells about the transverse (lateral) velocity distribution of the ship’s centre plane. The Pivot Point moves depending of the instantaneous set of forces acting on the ship.
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Position of Pivot Point During Swinging

With no forward speed and at steady rotational motion, when bow and stern swing in opposite directions the Pivot Point is located within the ship (often close to the midship).

When the ship is making headway, the Pivot Point moves forward. When the ship is making sternway, the Pivot Point moves aft.

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Position of Pivot Point Wnen the Ship is Making Headway/Sternway

Below picture shows how the Pivot Point position depends on block coefficient (slender ship vs full bodied ship).

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Position of Pivot Point Depending on Ship's Shape

Rudder Force & its Effect

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Hull Lateral Force Due to Sway

Transverse Trust of the Propeller

Ahead - Higher pressure on the port side transverse thrust causes small swing to port hardly noticeable.

Astern - Higher pressure on the starboard side much more significant transverse thrust causes swing to starboard.

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Ahead
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Astern

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Right Handed Propeller - Ahead and Astern
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Right Handed vs Left Handed
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Right Handed Propeller

Wedge Effect While Running Astern

Water is pushed by the propeller working astern in the narrow space between the ship and the jetty causing higher pressure to arise on the ship’s bow area. This results in creation a force F2 that may be larger than the transverse thrust F1. The ship swings then in the opposite direction to which is expected.
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The Ship Swings to the Opposite Direction

Effect of Thruster Forces

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The effectiveness of thruster depends on whether the ship is moving ahead or astern.

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Example: bow thrusters are more effective when the ship is moving astern

Rudder & Thruster Action

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Lateral motion to port
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Lateral motion to starboard

Effect of Tug Forces

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Forces Acting on the Ship When Turning

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