How to Inspect and Exercise Seacocks, Through-Hulls and Hose Clamps

With a flashlight, find every fitting below or near the waterline, inside and out. Photograph each one and note what it serves. Save the list in your BoatMend boat profile. Do not forget hard-to-reach ones behind panels, under the engine or in the head compartment.

Tie a tapered softwood plug of the right size to each seacock or through-hull with a short line. In a flood, you will not have time to look for one. BoatUS recommends keeping right-sized wooden plugs nearby.

Look at each valve. A proper seacock has a flange bolted to the hull and a lever handle. A round wheel handle that spins many turns is a gate valve. A hardware-store brass ball valve screwed onto the through-hull is an inline valve, not a seacock. Both can corrode or jam and give no clue whether they are open or closed. Mark them for replacement by a pro at the next haul-out.

Also look for these installation problems BoatUS sees in surveys:

• An inline valve screwed straight onto a through-hull. Many valves use tapered pipe threads, while most through-hulls use straight threads. The mismatch makes a weak joint that can loosen with vibration.
• A length of hose or pipe between the through-hull and the valve. That piece is unprotected: if it fails, there is nothing to close.
• A handle that can't swing through its full travel because cabinetry, a generator or other gear was installed in the way. If you can't reach or close a seacock in seconds, ask a yard about moving the equipment or fitting a remote handle.
• A seacock that is no longer used but still open to the sea. It should be closed and capped, or removed at haul-out.

Move each handle slowly from fully open to fully closed and back, several times. It should move smoothly through the full 90 degrees. Then try to wiggle the handle: it should have little or no play. BoatUS warns that a loose, wobbly handle can mean the shaft connecting it to the valve inside is corroded. If it is stiff, work it gently back and forth in small movements. Light taps with a rubber mallet on the handle base are OK; a big hammer or a long pipe for leverage is not. A handle that snaps off in the water is a real emergency.

If a seacock will not budge, leave it in whatever position it is in and do not force it. If it is stuck open, you have no way to shut off that hole in an emergency. Plan to haul out and have it serviced or replaced. Keep the plug for that fitting ready.

Check where the seacock or through-hull meets the hull inside. Look for weeping water, white or green crust, and cracks. On bronze, a pink or coppery color can mean the metal is losing its zinc (dezincification) and weakening. On plastic fittings, look for cracks around the nut. Any of these means a haul-out repair.

On metal seacocks, follow the green bonding wire (if fitted) to its terminal on the valve body. The connection should be tight and clean. A wire that is green inside the insulation or lumpy under it is corroded and should be replaced by someone who knows your boat's bonding system. Never just cut it off.

Squeeze the hose along its length. It should be firm but flexible. Replace it (at haul-out) if it is cracked, hard, mushy, swollen, kinked or the wire inside is rusting through. Old hoses can rot from the inside out, so age matters too: a BoatUS surveyor's rule of thumb is to replace seacock hoses at 10 years old regardless of how they look. Use the hose type made for that job (raw water, sanitation, exhaust or fuel), not household hose or thin bilge hose.

Hoses connected to below-waterline fittings should have two clamps where the fitting is long enough to hold both. ABYC strictly requires double clamps only on exhaust and fuel fill hoses, but BoatUS and surveyors recommend them below the waterline too (see /guides/hose-clamp-guide). Look at each clamp: both the band and the screw should be stainless. A rusty screw means a cheap clamp; replace it. Use a mirror to see the underside: BoatUS claims files show clamps often corrode on the bottom, where you can't see them from above. Don't forget the cockpit drain hoses; in one BoatUS claim a rotten cockpit drain hose sent a heavy rain into the bilge instead of overboard, and the boat sank at the dock. Check clamps are tight but not cutting into the hose, and that the hose is pushed fully onto the fitting.

Some seacocks (tapered-plug types and many ball valves) have a grease fitting or need periodic service. Use the grease the seacock maker recommends, and never one that contains graphite: BoatUS explains graphite causes fast galvanic corrosion of bronze and stainless parts. Taking a seacock apart is a haul-out job; on the water, only use an external grease fitting if your seacock has one.

At haul-out, a ball valve can be greased without taking it apart: close it, dab waterproof grease onto the ball from outside through the through-hull (a wooden dowel helps), and work the handle a few times. Before winter on land, some seacocks have a small drain plug on the body; removing it lets trapped water out so it can't freeze and crack the valve. Put it back before launch.

On engine intake lines, the strainer sits between the seacock and the engine pump. With the seacock closed, open the strainer, clean out weed and shells, check the lid gasket, and close it firmly. In spring, look closely at the bowl for cracks: BoatUS sees claims from strainers split by ice because they weren't drained in the fall, from lids not fully closed after winterizing, and from old corroded strainers that came apart underway. Reopen the seacock and check for leaks or air leaks at the lid when the engine runs.

With the boat out of the water, look at each through-hull from outside. Check that screens and scoops are clear of barnacles and that the flange sits flush and sealed against the hull. Look inside each opening with a flashlight to confirm nothing is blocking it. Check anything that has a separate bonding wire connected.

BoatUS recommends checking every through-hull for leaks right after the boat goes back in the water. Open the hatches and look at each fitting before you leave the ramp or the travel lift slings.

Schedule a haul-out with a yard if you find any seacock that will not close, any gate valve below the waterline, any weeping or cracked fitting, or any hose that needs replacing. Log what you found in BoatMend so the yard can fix it all in one trip.