Vessel Stability, Construction and Basic Engineering/Electrical Systems
Stability
Understand centre of gravity (G), centre of buoyancy (B) and metacentre (M). A vessel is stable when M is above G (positive GM). Learn the terms righting lever (GZ), angle of vanishing stability, free surface effect (free water in tanks or bilges reduces stability), list (permanent heel) versus heel (temporary), and the effect of loading high (raising G, reducing stability). Know that a beam wind and a following sea can be dangerous, and that overloading and free surface are common causes of capsize in small craft.
Construction
Know the common hull materials (GRP, aluminium, steel, wood), the difference between displacement and planing hulls, and the terms sheer, camber, deadrise, freeboard and draft. Understand buoyancy and flotation (foam-filled compartments), and the importance of watertight integrity and scuppers.
Engineering and electrical
Know the basic four-stroke and two-stroke cycles, the role of the impeller (cooling water), fuel filters and water separators, and the checks before starting (fuel, oil, coolant, bilge, battery). Understand 12 V DC systems, fuses and circuit breakers, battery isolation, charging (alternator) and the dangers of petrol vapour and battery hydrogen. Know the difference between AC shore power and DC on board, and the importance of RCD/earth leakage protection.
Traps
Questions often ask what happens to stability when a heavy weight is added high up (GM reduces, stability worsens) or when a tank is partly full (free surface effect). Remember that a planing hull needs power to stay on the plane, and that a two-stroke engine requires oil mixed with fuel.