Type of Hull
The hull refers to a waterproof body of a ship, flying boat, or boat. Some boats have open-top hulls, like dinghy-style vessels, while others have decks that cover the entire or a portion of the ship. Wet surface area and underwater resistance are governed by the length, width to depth ratio (Farrag, 2020a). The hull of this Ro-Ro ferry is 175.4 meters in length, 31.5 meters in width, and 6.7 meters in a draught. The rate at which a ship responds to the underwater resistance depends largely on its speed which is directly associated with the hull. This Ro-Ro ferry’s hull has a relatively squat dimension with a fairly shallow draught. Thus, its handling and maneuverability are not adversely affected by the type of hull used.
General Use of Helm and Power
The helm and power are vital in the control process as they are used to control the direction in which the ship is moving. A tiller or a wheel is the most common method of steering a boat. Being in charge of the boat’s helm is referred to as taking control of the helm. Usually, the helm entails the engine controls, a joystick, and the wheel that are used to power the ship (Farrag, 2020b). A primary mover and an alternator are used to create shipboard power. On board, an alternating current generator is employed.
Type of Engine and Propellers
The Ro-Ro Ferry has excellent maneuverability due to the presence of two medium-speed diesel engines, which have been connected by the gearboxes. This efficiency allows the engine to run in a specific direction, thereby enabling easier changing of the pitch from ahead to astern within the optimum revolution per minute (rpm) (House, 2007a, p. 44). When generators create 6600 kilo-volts of electricity, the supply transformer steps it down to the appropriate voltage for the motor in a pod (Anon, 2020a). However, the blade’s pitch takes much time to be changed by the hydraulics, thereby making it difficult and challenging. In terms of maneuverability, this twin-screw setup is extremely advantageous. The torque that may be generated by a pair of screws spinning around an axis is substantially larger than that of a single screw.
Type of Rudder
Located in the stern, the rudder is a component of a boat or ship’s steering system that is attached externally to the hull. The most frequent shape is a virtually flat, smooth surface of wood or metal attached to the sternpost. It is based on the idea that different water sources have different pressures. The Becker Flap Rudder is the most widely used rudder in the world and was developed by the company’s founder, Willi Becker, in the early stages of development (House, 2007b, p. 47). Ship maneuverability has never been better, thanks to his idea. Using a flap in the back, the Becker rudder provides 90 degrees of thrust at 45 degrees.
Bow Thruster
Bow thrusters are types of propellers though smaller in size and play a vital role in maneuverability. The vessel has a single tunnel bow thruster to provide transverse thrust. It is effective up to speeds of 6kts, primarily as faster than that, and water will struggle to enter the intake. A worm gear configuration is used to install the electric motor directly over the bow thruster. The engine operates at a constant speed, and the variable pitch blades are modified anytime the thrust or direction has to be changed (Farag, 2020c). For the vessel, thrusting will sternway will be effective, though not as effective as when the pivot is moved further forward. Additionally, bow thrusting might be less effective if the thrust is counteracted by a vacuum.
Pivot Point and Its Effect on the Maneuverability
The Pivot Point (PP) is a point around which a ship rotates axially. As the ship rotates, this point experiences no transverse velocity at all. In terms of kinematics, a Pivot Point is a reference point for the ship’s transverse (lateral) velocity. This pivot point slides forward as the ship makes progress. The Pivot Point shifts to the rear as the ship makes a sternway. However, the location of the pivot point will vary depending on the speed at which the ship or vessel is moving (Farag, 2020d). However, in the case of an effective and powerful lateral force on one end of the ship, the location of the pivot point tends to change and shift to about 1/3 of the ship’s length measured from the other ship’s end.
Slow Speed Control Using Engines and Rudder
During the slow speed control of a ship, there is always a need to ensure a reduction in the headway and stopping of the engine, thus allowing for plenty of time to adjust its positioning for the berth. However, at this moment, the biggest challenge is usually the probability of losing the rudder’s effectiveness at low speeds (Anon, 2020b). It is difficult to keep control of the ship’s head at low speeds, and also a lack of tug resistance to aid in reducing speeds (Farag, 2020c). Slow speed control, however, is achieved by utilizing a short but and applying full rudder of the engine power. This technique is often regarded as the kick technique and is associated with some pitfalls which may later result in increased speeds, thus making it difficult to control the speeds.
Maneuvering the Ferry Off the Berth and Going out of Stern
In my opinion, the safest maneuver would be to use the bow thruster to create lateral thrust by pushing the bow to port, with the helm at hard-to-starboard to create rudder pressure resulting in thrust to port and use just the port engine with the propeller pitched ahead. This would be performed at dead slow ahead, at barely a knot, just enough to generate flow over the rudders (Farag, 2020e). Whilst creating lateral movement, the vessel would also creep very slowly ahead. This movement would move the pivot point from the LCG to the foremost point of the WL, to 1/4 of the WL aft of the forward point.
The variable pitch propellers’ wide rpm range and quick response time allow me to midship the rudders and operate both engines in dead slow astern once the vessel is perfectly oriented for a safe astern escape into the swinging region. Once the vessel starts moving again, the PP would perform the identical actions as before, but this time from the vessel’s stern end. It is a little more difficult to maintain a desired course behind the boat because of its less-fine stern shape and higher resistance to water. Reducing the steering lever also affects steering, but if the vessel is traveling at a dead slow speed behind, it should be able to maintain her course and use the bow thruster to keep the bow in control, employing the bow thruster-PP lever to help to steer in this situation (House, 2007c). If I could, I would increase the speed to 1-2kts and keep the PP at 1/4 WL.
Once the vessel is at the turning point, the port engine can be put to kick ahead and the starboard engine astern, thereby creating torque in a clockwise direction. When the vessel is on the correct heading, the rudders can be moved to midships (perhaps using some counter rudder to stop the momentum of the turn), and the vessel can begin to make headway on its desired course.
Reference List
Anon, 2020a. Wartsila Encyclopaedia of Marine Technology: Bow Thruster. Web.
Anon, 2020b. Wartsila Encyclopaedia of Marine Technology: Rudder. Web.
Farrag, A., 2020a. Command Management: Berthing and unberthing plans. Web.
Farrag, A., 2020b. Command Management: Pivot point. Web.
Farrag, A., 2020c. Command Management: Ship Handling Characteristics. Web.
Farrag, A., 2020d. Command Management: Ship Manoeuvring Characteristics A. Web.
Farrag, A., 2020e. Command Management: Twin Screw Work. Web.
House, D. J. (2007a). Controllable pitch propellers (CPP). In: Ship Handling: Theory and Practice. Amsterdam: Elvesier Ltd.
House, D. J. (2007b). The ship’s pivot point. In: Ship Handling: Theory and Practice. Amsterdam: Elsevier Ltd.
House, D. J. (2007c). Twin screw vessels. In: Ship Handling: Theory and Practice. Amsterdam: Elvesier Ltd.