Leaks can be hard to trace. Sometimes there’s a “snail trail” to follow, but often the drip is a long way from the leak itself. Don’t ignore small leaks, as they can soak into wood or upholstery and cause lots of damage. A headlamp and mirror are useful, and if you’re working alone take a cell phone in case you get stuck in a tight spot.
Leaks can occur anywhere there’s a hole, or simply some weakness, in the structure of the boat. Here are some likely culprits: A. Rail and stanchion bases—especially if they’ve taken a knock; B. Hatches; C. Windows; D. Hull/deck joint; E. Tanks (taste or test for salt water, and take care with holding tanks) F. Seacocks; G. Transducers; H. Keel bolts; I. Through-hulls above the static water line; J. Vented anti-siphon loops; K. Cooling water joints, hoses and exhaust elbows; L. Stern gland (remember that traditional stuffing boxes should weep slightly); M. Rudder gland.
N An old plastic through-hull can harden with age and may crack inside the hull, especially if there’s a heavy unsupported hose connected to it. A typical problem is a bilge pump outlet that leaks when the pump is used or when the fitting is heeled below the water.
O Some plastics can crack after years of UV exposure. The cracks can be hard to spot, and you may need to wriggle the fitting a bit to find them.
P Poor sink fittings can crack and leak. They might also sink the boat if the exhaust hose comes loose and falls below the waterline.
Q Never ignore stains on seacocks, as they may indicate dezincification of the metal in the valve body. Look for a rose-colored tint under the green verdigris. Some poor-quality ball valves only last a few seasons and can break off.
R Bronze seacocks can last for decades if they are serviced every year and are kept well greased. Note the grease nipple, two hose clamps and locknuts.
S Vented loops are usually tucked up high in the hull where they are often neglected. Check the valve regularly.
T Stanchion base and hull/deck joint leaks are hard to sort out because they may only be active on one tack. They’re also hard to get at. Moisture-curing glue can be used as a temporary fix at sea, but a flexible polyurethane sealant/adhesive is best.
Illustrations by Dick Everitt