Plumbing, heads, holding tanks and seacocks

What to inspect · Power & sail

Water leaking in through fittings below the waterline sinks more boats at the dock than anything else. Check every through-hull, valve, hose and clamp, and find out how the head and holding tank are plumbed, because federal sewage rules apply to every boat with an installed toilet.

Through-hulls and seacocks

• ABYC's standard calls for a seacock on every hose or pipe through the hull below the heeled waterline (7 degrees of heel for powerboats; heeled to the deck edge amidships for sailboats), built to the UL sea-valve standard.
• An ordinary in-line ball valve screwed onto a through-hull is not a proper seacock: the straight and tapered threads don't match and the joint is weak. Look for flanged bronze or reinforced-plastic seacocks, not brass or PVC.
• Gate valves are common on older boats. You can't see whether they are open or shut, and they can fail inside. Work every valve on survey day; a seized one needs attention.
• Plastic through-hulls near the waterline turn brittle in sunlight and can crack.

Hoses and clamps

• Hoses below the waterline should be the reinforced kind, not light unreinforced PVC, and double-clamped with stainless clamps. Replace rusty clamps and stiff, cracked or soft hoses.
• In BoatUS claims, half of dockside sinkings came from leaks at underwater fittings: stuffing boxes first, then sterndrive bellows, hoses and clamps, strainers and drain plugs.

Heads and holding tanks

• Coast Guard rules (33 CFR 159) require every boat with an installed toilet to have a working, certified marine sanitation device. Type I and II units treat sewage (Type I only on boats 65 feet or less); Type III is a holding tank.
• In no-discharge zones any overboard path must be secured, for example by closing the seacock and removing the handle, padlocking it, or using a wire tie that can't be released.
• On an older boat, trace the head plumbing: is there a holding tank, a deck pump-out fitting, a Y-valve to overboard? Ask when the sanitation hoses were last replaced.

Other water systems

• Check raw-water strainers (ice can bend one), air-conditioning and generator intakes, and the fresh-water pump, tanks and water heater.
• Transducers and speed sensors are holes in the hull too. Removable ones must be locked in place so they can't work loose.

General guidance for recreational boaters, researched from the sources listed and written in our own words. Your equipment manuals, local knowledge, the Navigation Rules and a qualified instructor come first.