Parts of a Boat

Electrochemical corrosion that occurs when dissimilar metals are electrically connected in an electrolyte such as seawater. The less noble metal becomes anodic and corrodes preferentially. Material selection, electrical isolation, coatings and correctly designed sacrificial anodes help control the process without replacing inspection and maintenance.

The direction in which tension from a rope, cable or tackle acts on a load and its fittings. Changing the lead changes the direction and sometimes the magnitude of forces on fairleads, blocks and attachment points. Crew should remain clear of loaded lines and the areas that could be swept if a component fails.

The formation and collapse of vapour cavities where local water pressure falls below the liquid’s vapour pressure. It can occur around fast-moving propellers, rudders, pumps and hydrofoils, causing noise, vibration, loss of efficiency and surface erosion. It differs from ventilation, in which air is drawn down from the water surface.

A storage compartment accessed from a vessel’s cockpit. It may hold warps, fenders, safety equipment or machinery, but contents must be secured and kept clear of controls and drains. Lockers opening into the hull require appropriate closure, drainage and gas-safety arrangements for what is stored.

A line led forward from a boom or spinnaker pole to restrain upward or aft movement. On a spinnaker pole it works with the topping lift and afterguy or brace to control pole height and position. Leads, fittings and release arrangements must suit the loads and permit safe handling during manoeuvres.

A sailing rig in which the forestay attaches below the masthead. The arrangement can improve control of mast bend and mainsail shape and may use swept spreaders or running backstays for support. The fractional designation describes the approximate height of the forestay attachment relative to the mast.

An arrangement of rope and one or more pulley blocks used to gain mechanical advantage or redirect a load. The number of supporting rope parts determines the ideal purchase, while friction reduces the advantage achieved in practice. The rope, blocks, attachments and operating method must all be suitable for the expected load.

A vessel with two or more principal hulls arranged side by side. Catamarans have two hulls and trimarans three, generally gaining form stability and deck area with relatively low wetted surface. Their handling, loading, capsize behaviour, marina requirements and response to waves differ from those of comparable monohulls.

A riding turn in which a loaded rope traps itself under another turn on a winch drum. Overrides commonly result from an unsuitable lead angle, slack entering the drum or poor tailing. Load should be controlled before the trapped turn is cleared, using a safe alternative line or unloading method rather than placing hands near…