10.8 Manoeuvring diagrams
Define:
- Advance
- Transfer
- Tactical diameter
- Track reach
- Stopping distance
- Turning circles at various draughts and speeds
Explain
- The effects of displacement, draught, trim, speed and under-keel clearance on turning circles and stopping distances
- Effect of transverse thrust on turning circle of the ship with right/ left handed propeller.
Definitions:
Advance: The distance made good in the direction of the intended track during a turning maneuver. It represents the horizontal movement of the ship.
Transfer: The lateral movement of the ship from the initial heading to the final heading during a turning maneuver.
Tactical diameter: The diameter of the circle that the ship follows during a turning maneuver, which is the sum of the advance and transfer.
Track reach: The distance made good in the direction of the intended track from the initial position to the final position of the ship during a stopping maneuver.
Stopping distance: The distance traveled by the ship from the time the engines are put astern until the ship comes to a complete stop.
Turning circles at various draughts and speeds: The paths followed by the ship during a complete 360-degree turn at different draughts (ship's draft or depth in the water) and speeds.
Explanation:
The effects of displacement, draught, trim, speed, and under-keel clearance on turning circles and stopping distances: The ship's displacement, draught (the depth of the ship below the waterline), trim (the longitudinal balance of the ship), speed, and under-keel clearance (the distance between the bottom of the ship and the seabed) all affect the ship's maneuvering characteristics. These factors influence the ship's ability to turn, stop, and maneuver safely.
For example, a ship with a larger displacement or draught may have larger turning circles and stopping distances compared to a smaller ship.
Similarly, higher speeds and reduced under-keel clearance can impact the ship's maneuvering performance and safety.
Effect of transverse thrust on the turning circle of the ship with right/left-handed propeller: Transverse thrust refers to the sideways force generated by the ship's propeller. In a ship with a right-handed propeller (rotating clockwise when viewed from astern), the transverse thrust tends to push the ship's stern to the port side, resulting in a smaller turning circle to starboard (right). Conversely, in a ship with a left-handed propeller (rotating counterclockwise when viewed from astern), the transverse thrust pushes the ship's stern to the starboard side, resulting in a smaller turning circle to port (left). The effect of transverse thrust needs to be considered by ship handlers during maneuvers to ensure safe and efficient navigation.
Maneuvering Logic
The turning circle of a ship is influenced by several factors, and one significant factor is the fullness of the bow volume under water. Ships with a greater bow volume have more resistance to water flow right up forward. This increased resistance creates a greater turning effect, allowing the ship to execute tighter turns.
For example, a bulk carrier ship typically has a substantial bow volume under water, resulting in increased resistance to water flow in the forward region. Consequently, the ship experiences a stronger turning force, enabling it to navigate through tighter turns compared to other ship types. This is because the greater resistance generated by the bow volume contributes to a shorter turning circle.
On the other hand, a container ship often features a streamlined or arrow-shaped bow region under water, which reduces the resistance to water flow. As a result, the turning circle of a container ship is generally larger compared to a bulk carrier ship due to the reduced turning force caused by the lesser resistance from the bow volume.
In contrast, a cuboidal barge, with its box-like shape and significant bow volume under water, experiences even greater resistance to water flow. Consequently, the turning circle of a cuboidal barge is typically tighter than that of both bulk carriers and container ships.