A seaworthy ship refers to a vessel capable of transporting cargo from one place to another without any danger or damage to both the ship and its cargo. However, heavy lift cargoes can significantly impact the seaworthiness of a ship. Proper securing of these cargoes is crucial and should adhere to the cargo securing manual and the code for safe practice for cargo stowage and securing. Failure to secure the cargo adequately can lead to shifting during severe weather conditions, resulting in a heavy list at sea and potentially causing the vessel to capsize. Additionally, heavy lifts can damage a ship’s watertight integrity, leading to flooding. The load density of the tank top should be able to support the weight of heavy cargo without causing any structural damage. It’s worth noting that if the vessel utilizes its own gear to load or unload cargo, there can be a significant loss of GM (metacentric height), as the crane lifting the load causes a shift in the center of gravity, resulting in a reduced GM.
Effects of Heavy Lifts on Stability:
1. When a weight is loaded onboard the vessel, the ship’s center of gravity (G) will move towards the loaded weight.
2. As the weight is lifted, its effective weight acts from the head of the derrick, causing the ship’s center of gravity (G) to move upward.
3. This upward movement of the center of gravity reduces the metacentric height (GM) of the vessel, making it less stable than before.
4. Consequently, depending on the circumstances, it is advisable to lower the position of the ship’s center of gravity (G) to anticipate the rise in GM prior to a heavy lift operation.
By ensuring proper cargo securing, considering the impact on stability, and taking necessary precautions to maintain the vessel’s stability parameters, ships can mitigate the potential risks associated with heavy lifts, enhance their seaworthiness, and ensure the safe transportation of cargo.
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