10.3 Berthing and Unberthing
Describe:
- the effects of right- and left-handed propellers on manoeuvring
- the use of twin screws for manoeuvring
- the advantages and disadvantages of controllable-pitch propellers with regard to ship handling
- the use of lateral thrusters (bow & stern)
- how an anchor or anchors may be used to assist in manoeuvring
- the different ways in which tugs may be made fast and used
- Berthing and Unberthing under various conditions of wind, tide and current (with & without tugs)
- Types of rudder (Flap rudder, Rotor rudder, T-shaped rudder and Twin Schilling rudders)
Effects of right- and left-handed propellers on maneuvering:
The rotation direction of the propeller, either right-handed (clockwise) or left-handed (counterclockwise), has an impact on a vessel's maneuvering characteristics. These effects are most noticeable at low speeds and during maneuvers, such as turning or docking.
Right-Handed Propellers: With a right-handed propeller, the vessel tends to turn to the left when in reverse and turn to the right when moving forward. This effect is known as "propeller walk" and is caused by the rotational forces generated by the propeller. It can influence the vessel's turning radius and require adjustments in maneuvering.
Left-Handed Propellers: Similarly, a vessel equipped with a left-handed propeller will tend to turn to the right when in reverse and turn to the left when moving forward. The propeller walk effect is opposite to that of a right-handed propeller.
Use of twin screws for maneuvering:
Twin screws, or twin propellers, refer to a propulsion system with two independent propellers, each driven by a separate engine or motor. Using twin screws provides several advantages for maneuvering:
Increased Maneuverability: Twin screws allow for independent control of each propeller, enabling differential thrust and enhanced maneuvering capabilities. By varying the rotational speed or direction of each propeller, the vessel can perform tight turns, move sideways (crabbing), or rotate around its own axis (pivot).
Redundancy and Safety: With two independent propulsion systems, twin screws provide redundancy in case of a single propeller failure, reducing the risk of complete loss of propulsion and enhancing vessel safety during critical maneuvers.
Improved Station-Keeping: Twin screws facilitate better control and precise positioning, which is particularly beneficial in challenging conditions, such as strong currents or tight maneuvering situations.
However, it is important to note that twin screws may increase initial vessel construction and operational costs due to the additional propulsion equipment required.
Advantages and disadvantages of controllable-pitch propellers (CPP) with regard to ship handling:
Controllable-pitch propellers (CPP) allow for variable pitch adjustment of the propeller blades, providing flexibility in ship handling. The advantages and disadvantages of CPP systems include:
Advantages:
Improved Maneuverability: CPP allows for instant adjustment of propeller pitch, enabling precise control over thrust and vessel response during maneuvers, such as acceleration, deceleration, and changes in direction.
Optimized Efficiency: CPP permits optimal propeller pitch adjustment based on operating conditions, maximizing propulsion efficiency and reducing fuel consumption.
Reduced Vibrations: CPP systems can help mitigate propeller-induced vibrations, enhancing onboard comfort for passengers and crew.
Enhanced Power Management: CPP facilitates load sharing between multiple engines and propellers, optimizing power distribution and improving overall propulsion system performance.
Disadvantages:
Increased Complexity: CPP systems are more complex than fixed-pitch propellers, requiring additional machinery and control systems. This complexity may result in higher installation, maintenance, and repair costs.
Higher Initial Investment: The initial cost of a vessel equipped with CPP systems may be higher compared to vessels with fixed-pitch propellers.
Technical Challenges: CPP systems require careful monitoring and maintenance to ensure proper pitch control and prevent potential issues, such as blade fouling or loss of pitch control.
Use of lateral thrusters (bow & stern):
Lateral thrusters, including bow thrusters and stern thrusters, provide additional maneuvering capabilities, especially in restricted waters or challenging docking scenarios. These thrusters are typically transversely mounted propulsion units located in the bow or stern areas of a vessel.
Bow Thrusters: Bow thrusters are installed in the forward section of the vessel and generate a lateral thrust perpendicular to the vessel's longitudinal axis. They assist in sideways movement, enabling improved maneuverability during docking or tight maneuvers.
Stern Thrusters: Stern thrusters are installed in the aft section of the vessel and provide a lateral thrust parallel to the vessel's longitudinal axis. They facilitate enhanced maneuvering control, particularly during berthing or undocking operations.
The use of bow and stern thrusters allows vessels to move laterally, improve control in confined spaces, and compensate for the effects of wind, current, and restricted maneuvering areas. They reduce the reliance on main propulsion systems and rudder alone, enhancing the safety and efficiency of vessel operations.
How an anchor or anchors may be used to assist in maneuvering:
Anchors can be used strategically during maneuvering operations to assist in controlling the vessel's movement, especially in adverse conditions or restricted areas. Here are some scenarios where anchors may be utilized:
Station Keeping: In situations where a vessel needs to maintain a fixed position or hold its position against wind or current, deploying one or more anchors can provide additional stability and resist the forces acting on the vessel.
Rounding Bends or Navigating Narrow Channels: By deploying the anchor(s) selectively, vessels can use the anchor as a pivot point to assist in rounding bends or navigating narrow channels. The anchor can be set at an angle to the vessel's longitudinal axis, helping to adjust the vessel's heading and minimize drift.
Emergency Stopping: In emergency situations where the vessel needs to come to an immediate stop, dropping one or more anchors can provide significant resistance to forward movement and aid in stopping the vessel more quickly.
Different ways in which tugs may be made fast and used:
Tugs play a crucial role in assisting vessels during maneuvering operations, particularly in restricted waters or challenging port conditions. Tugs can be made fast to the vessel using various methods, including:
Towline: The most common method involves connecting a towline between the tug and the vessel. The towline is secured to strong points on the vessel's hull, such as bitts or towing points, and to the tug's winch or towing gear. Tugs can apply pulling or pushing forces to aid in steering, braking, or guiding the vessel.
Towing Bridle: A towing bridle is used when multiple tugs are employed. It consists of two or more towlines connected to the vessel at separate points, creating a spread between the tugs. The bridle configuration allows for better control and maneuverability, distributing the towing forces evenly.
Pushing: In some cases, tugs may be used to push against the vessel's hull. This technique is commonly employed during berthing or undocking maneuvers, where the tug applies significant lateral force to assist in steering or controlling the vessel's movement.
The selection of the specific tug maneuvering technique depends on factors such as vessel size, shape, maneuvering requirements, local regulations, and the expertise of tug operators. Effective communication and coordination between the vessel's crew and tug operators are crucial to ensure safe and efficient maneuvering operations.
Types of rudders (Flap rudder, Rotor rudder, T-shaped rudder, and Twin Schilling rudders) with reference to the provided maritime regulation excerpt:
The maritime regulation excerpt you provided, while informative about maneuverability standards, does not directly define the mentioned types of rudders. However, I can provide a brief description of these rudder types:
Flap Rudder: A flap rudder incorporates a trailing-edge flap on the rudder blade that can be controlled to vary its effective area. By adjusting the flap position, the lift and drag characteristics of the rudder can be modified, providing enhanced maneuverability and steering response.
Rotor Rudder: A rotor rudder consists of a rotating cylindrical body at the trailing edge of the rudder blade. The rotation of the cylindrical body generates a side force, assisting in maneuvering and reducing the vessel's turning radius.
T-shaped Rudder: A T-shaped rudder has a configuration resembling the letter "T" when viewed from the side. This design provides increased lateral surface area, improving maneuvering performance and control, especially at low speeds or during tight turns.
Twin Schilling Rudders: Twin Schilling rudders consist of two rudders placed on both sides of the propeller, providing better maneuverability and steering capabilities. This arrangement helps improve the vessel's handling characteristics, particularly in restricted waters or when precise maneuvering is required.