Vessel Construction, Stability and Equipment
Construction basics
Know the main hull forms, materials and structural elements: keel, frames, stringers, bulkheads, deck and superstructure. Understand watertight subdivision and why bulkheads limit flooding. Learn the difference between displacement, semi-displacement and planing hulls and how each behaves in waves. Understand the purpose of bilge systems, seacocks and skin fittings.
Stability
Candidates must understand centre of gravity, centre of buoyancy, metacentric height and the righting lever. Know the difference between initial and overall stability, the effect of free surface, and how adding weight high or low changes stability. Understand freeboard, reserve buoyancy, and the dangers of overloading and of water trapped on deck. Know the meaning of list versus heel and how to correct each.
Equipment
Know the required equipment for your vessel class: anchor, mooring lines, fenders, navigation lights, sound signals, firefighting equipment, life-saving appliances, and documentation. Understand inspection and maintenance obligations.
Traps
- Confusing list with heel.
- Ignoring free surface effect from partly filled tanks.
- Assuming more weight low always improves stability in every condition.
- Forgetting that watertight doors must be closed to preserve subdivision.
Worked rule of thumb
For any stability question, ask where the weight is added and whether free surface exists. Weight added high reduces stability; weight added low generally improves it. Free surface always reduces stability regardless of position.