(a) Describe stability requirement for dry-docking.
(6)
(b) A box shaped vessel, 50 metres long x 10 metres wide, floats in salt water on an even keel at a draft of 4 metres. A center line longitudinal watertight bulkhead extends from end to end and for the full depth of the vessel. A compartment amidships on the starboard side is 15 metres long and contains cargo with permeability 30%. Calculate the list if this compartment is bilged. KG = 3 metres.
(10)
Reference Answer
### Part (a): Stability Requirement for Dry-docking For a vessel to be safely dry-docked, specific stability criteria must be met before, during, and after the operation. The entire process involves a gradual transfer of the vessel's weight from hydrostatic support (buoyancy) to physical support (dock blocks), which significantly affects its stability. 1. **Positive Initial Stability (GM)**: Before the process begins, the vessel must have a positive metacentric height (GM). A recommended minimum GM of 0.15m to 0.3m is generally required, depending on the vessel's size, type, and the prevailing weather conditions. This ensures the vessel can withstand any initial listing moments as it enters the dock. 2. **The Critical Instant**: The most critical moment occurs when the vessel's keel first makes contact with the blocks. Typically, vessels are docked with a slight trim by the stern, so the aft section touches first. At this point, the dock blocks begin to exert an upward force, known as the P-force or upthrust.
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