MIDTERM Seam5 Topic 3.pdf

Practical Use of Ship’s Turning Circle The turning circle of a ship is a fundamental aspect of its maneuverability and has several practical applications: Navigating Narrow Channels and Ports Precision: Knowing the turning circle helps in planning precise maneuvers in confined spaces, such as narrow...

Practical Use of Ship’s Turning Circle The turning circle of a ship is a fundamental aspect of its maneuverability and has several practical applications: Navigating Narrow Channels and Ports Precision: Knowing the turning circle helps in planning precise maneuvers in confined spaces, such as narrow channels, harbors, and ports. Safety: It ensures the ship can turn without colliding with other vessels, structures, or the shore. Avoiding Collisions Emergency Maneuvers: In situations where a collision is imminent, understanding the turning circle allows the crew to execute quick and effective turns to avoid other ships or obstacles. Traffic Management: Helps in managing traffic in busy waterways by predicting how much space a ship will need to turn. Docking and Undocking Alignment: Assists in aligning the ship with docks or piers, ensuring smooth docking and undocking operations. Tug Assistance: Helps in coordinating with tugboats, which often assist in turning large vessels in tight spaces. Pilotage Pilot Knowledge: Pilots use the turning circle information to guide ships safely through challenging navigational areas. Training: Essential for training ship pilots and crew in handling the vessel under various conditions. Route Planning Efficient Routing: Helps in planning routes that minimize the need for sharp turns, thereby saving time and fuel. Environmental Considerations: Ensures that turns are planned to avoid environmentally sensitive areas. Regulatory Compliance Adherence to Standards: Ensures compliance with international maritime regulations, such as those set by the IMO, which mandate the display of maneuvering information. Safety Audits: Used during safety audits and inspections to verify that the ship can perform required maneuvers safely. Effects on Ship’s Turning Circle and Stopping Distances 1. Deadweight refers to the total weight a ship carries, including cargo, fuel, passengers, and crew. Turning Circle: A ship with a higher deadweight will generally have a larger turning circle due to increased inertia. The added weight makes the ship less responsive to the rudder, requiring more time and distance to complete a turn. Stopping Distances: Heavier ships take longer to stop because of the greater momentum. The stopping distance increases significantly with higher deadweight, especially in emergency stop situations. 2. Draught is the vertical distance between the waterline and the bottom of the hull, while trim refers to the difference in draught between the bow and stern. Turning Circle: A deeper draught increases water resistance, making the ship slower to respond to steering inputs, thus enlarging the turning circle. Trim also affects turning; a ship trimmed by the stern (deeper at the stern) will have a larger turning circle compared to one trimmed by the bow. Stopping Distances: Greater draught increases the hydrodynamic resistance, which can help slow the ship down faster. However, improper trim can negatively impact stopping efficiency, with a stern-heavy trim generally increasing stopping distances. 3. Speed is the rate at which a ship moves through the water. Turning Circle: At higher speeds, the turning circle tends to be larger because the ship covers more distance before completing the turn. However, the rudder’s effectiveness increases with speed, which can somewhat counteract this effect. Stopping Distances: Higher speeds result in significantly longer stopping distances. The kinetic energy of the ship increases with the square of its speed, meaning a ship moving at twice the speed will have four times the stopping distance. 4. Under-Keel Clearance (UKC) is the distance between the ship’s keel and the seabed. Turning Circle: Reduced UKC can increase the turning circle due to the squat effect, where the ship sinks deeper into the water as it moves, increasing resistance and reducing maneuverability. Stopping Distances: Shallow waters increase stopping distances because of increased hydrodynamic resistance and the potential for the ship to squat, which can affect propulsion and steering efficiency. The provision and display of maneuvering information recommended in Assembly resolution A.601(15) The IMO Standards for Tactical Diameter and Advance of a ship RESOLUTION MSC.137(76) (adopted on 4 December 2002) STANDARDS FOR SHIP MANOEUVRABILITY Tactical Diameter Definition: The tactical diameter is the distance a ship travels perpendicular to its original course when making a 180-degree turn. Standard: The IMO requires that the tactical diameter should not exceed 5 ship lengths. This ensures that ships can turn within a reasonable distance, which is crucial for avoiding obstacles and navigating confined spaces. Advance Definition: Advance is the distance a ship travels along its original course before completing a turn. Standard: The IMO specifies that the advance should not exceed 4.5 ship lengths. This standard helps ensure that ships can change direction efficiently without covering excessive distance. Factors Influencing Tactical Diameter and Advance Several factors can affect a ship’s tactical diameter and advance, including: Ship Design: The length, beam, and hull shape of a ship can influence its turning ability. Rudder Size and Type: Larger rudders or advanced rudder designs can improve turning performance. Speed: Higher speeds generally result in larger turning circles and advances. Environmental Conditions: Wind, current, and wave action can impact a ship’s turning performance. Factors affecting the ship’s turning circle Maneuvering is one of the critical aspects of any vessel. It is defined as the capability of a ship to change its course or heading from its previous trajectory. Any ship must be able to turn or change its directional sense as and when required. The requirements can be: Changing its course or heading from time to time. Changing its direction of voyage or route due to weather, uncongenial sea conditions, or internal reasons about the ship itself Maintaining a desired course or trajectory. Sailing in meandering courses like rivers, channels, canals, etc. Avoiding obstacles like landmasses, bergs, reefs, offshore structures, and other vessels Circling some point like a port or terminal or an island due to unavailability of berths, tidal conditions, rough sea or weather conditions, or marine traffic. After the vessel is launched, manoeuvring trials take place as a part of the sea trials and help assess the vessel’s manoeuvring ability and performance under different modes of operation. These manoeuvring trials are based on the plausible manoeuvres the ship must undergo during its lifetime under different situations it may encounter. As per the guidelines for manoeuvring trials from the MSC 76 codes of IMO, all sea-going vessels above 100 metres in length are required to undergo these manoeuvring trials. And irrespective of length, all gas and chemical tankers must undergo them after launching and before delivery to the client. What is a Turning Circle? Imagine driving your car on empty, flat ground. Slowly start turning the steering wheel and keep it fixated at a certain position. The car turns in the direction where the wheel is turned and starts making a circle of radius. Or even simpler, start running on a football field or an open ground. Start turning towards a side. If you do not turn forward again, you tend to keep going in circles about the same point, isn’t it? That’s the simple law of nature: any finite object constantly tending to turn towards a particular side makes a circular trajectory! But from the simpleton laws of nature again, the smallest circle traced by any object or body is directly related to the size of the body. In other words, the minimum radius or diameter of the circle traced by a turning body increases with  size because this depends on the locus of the centroid of the moving body. From common sense, the smallest circle traced by you running on a field will be far smaller than a constantly turning SUV! Factors Affecting The Turning Circle Now, let us explore the factors influencing the vessel’s turning circle considering a fixed turning moment. Size and Extent of the Vessel: Larger vessels generally have larger turning circles due to their increased inertia and hydrodynamic resistance. Example: A large container ship like the Ever Given (which famously blocked the Suez Canal) has a much larger turning circle compared to a smaller vessel like a tugboat. The sheer size and mass of the Ever Given make it less agile. Hull Form: The shape of the hull affects water flow around the vessel. Streamlined hulls typically have smaller turning circles compared to bulkier designs. Example: A cruise ship with a streamlined hull designed for speed and efficiency will have a smaller turning circle compared to a bulk carrier with a boxier hull designed to maximize cargo space. Draft and Trim: A deeper draft increases hydrodynamic resistance, making the vessel less responsive to steering inputs. Trim, or the difference in draft between the bow and stern, also plays a role. A vessel trimmed by the stern usually turns more effectively. Example: A vessel with a deep draft, such as an oil tanker, will have a larger turning circle compared to a vessel with a shallow draft, like a ferry. Additionally, a ship trimmed by the stern, such as a naval destroyer, will turn more effectively than one trimmed by the bow. Available Depth: Shallow waters can increase the turning circle due to increased resistance and the potential for grounding. Example: In shallow waters, a cargo ship might experience increased resistance, leading to a larger turning circle. This is why harbor pilots are crucial for navigating large vessels in ports with limited depth. Propulsion and Machinery: The type and power of the propulsion system affect maneuverability. More powerful engines and advanced propulsion systems like azimuth thrusters can reduce the turning circle. Example: A modern cruise ship equipped with azimuth thrusters can turn in a much tighter circle compared to a traditional cargo ship with a fixed propeller and rudder system. Rudder Moment Applied: The angle and size of the rudder determine the effectiveness of the turn. Larger rudder angles and more powerful rudders result in tighter turns. Example: A sailing yacht with a large, responsive rudder can make sharp turns, whereas a large bulk carrier with a smaller rudder relative to its size will have a more gradual turn. Displacement and Cargo Distribution: Properly distributed cargo ensures better stability and maneuverability. Uneven distribution can lead to sluggish responses. Example: A container ship with evenly distributed cargo will maneuver more predictably than one with unevenly loaded containers, which can cause sluggish or unpredictable turning behavior. Speed: Higher speeds generally result in larger turning circles due to increased centrifugal forces. However, at very low speeds, the vessel may also become less responsive. Example: A high-speed ferry traveling at full speed will have a larger turning circle due to increased centrifugal forces, whereas the same ferry at lower speeds will turn more sharply. External Forces and Wind Conditions: Wind, currents, and waves can significantly affect the turning circle by altering the vessel’s drift and stability. Example: A sailing vessel in strong winds will have its turning circle affected by the wind’s direction and strength. Similarly, a large tanker navigating through a strong current will experience drift, altering its turning path.