Emergency seacock repair: How to stop a below-waterline leak

Roger Hughes struggles with a potentially disastrous snapped off skin fitting

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During an evening visit to my schooner Britannia, floating quietly in her cosy dock at Fairfield Harbour in North Carolina, I heard the bilge pump running more-or-less continuously, being activated by the float switch in the lowest part of the bilge. There was obviously a water leak somewhere, probably within the complicated plumbing or the AC cooling pipes.

This happened periodically, and I was not too concerned. It didn’t take more than a few minutes to trace the gushing leak to the seacock feeding the pump for the twin AC systems. The seacock is in the centre of a row of three, about 30in below the waterline. Water was spurting out through the reinforcing caulk below the valve itself and I suddenly became very concerned because I could see that the leak was below the closed ball valve – not a good place to have a leak because closing the valve will not stop it.

Caulk cracked around a seacock which needs repairs

The threaded stem was encased in hard caulk that had cracked and the stem was also sheared – an emergency seacock repair was needed. Credit: Roger Hughes

Also, the bilge pump was only just keeping pace with the increasing inflow. The valve stem was encased all round in solid caulk that had somehow split. I pressed the valve down with my hand and the flow diminished, but immediately increased when I released the pressure.

Emergency measures

I tried to wedge a piece of wood in to press the two pieces together, but it kept slipping off the top of the round valve fitting. I then succeeded in stemming the flow a little by wrapping the valve with duct tape. I also had the usual assortment of tapered wooden bungs, but I was afraid to disturb the valve in case it broke completely off, and I didn’t have a bung to fit into the gushing hole.

A broken seacock needing a repair

The complete valve assembly had parted from the through-hull stem. Credit: Roger Hughes

At that moment, I dared hardly touch the valve. The obvious answer would be to shove a bung into the seacock from the outside of the hull. Using the boarding ladder I slid into the warm, still water directly opposite where I thought the seacock was located and hoped to be able to push a bung into the seacock, but I couldn’t feel the opening and even by taking a deep breath and diving deeper I still couldn’t find the hole, and I might not have been able to push it into the hole anyway.

I climbed out, soaking wet and thought I’d better get some help. Fairfield Harbour Yacht Club has an emergency help committee and as the word went out two members brought portable pumps in case they were needed. My boating friend George Stateham’s opinion was unequivocal: “Get a diver over here quick to fit a bung properly and stop it, then you’ll be able to remove and inspect the inside fracture.”

Rescue diver

Kurt Hathaway arrived half an hour later – it’s definitely very handy to have a diver living near where your boat is docked. He was over the side in a jiffy with a handful of bungs since I wasn’t sure which size would fit. “All of these are too big”, spluttered Kurt.

I only had one more which I hadn’t given him because I thought it would be too small, but it fitted perfectly; after only a few taps with a hammer it was wedged in place and the water ingress stopped. Phew! I could start breathing again. I had thought about sleeping on the boat to keep an eye on the temporary fix, but the leak was on the air conditioning inlet seacock so I wouldn’t be able to run the AC and inside it was 95°F/35°C, so there’d not have been much sleep for me that night. I was totally exhausted, both physically and mentally, so after satisfying myself that the leak had been sealed and that little more could be done I went home, had a stiff Scotch and went to bed.

Seacock repair

Early the next morning, I was back on Britannia. I was very pleased to see the area around the valve had completely dried out. I carefully cut off my crude duct tape bandage and removed the pipe to the AC filter bowl so I could completely lift the top of the valve off the through-hull stem. Amazingly, it took very little effort to pull apart and had only been held in place by the caulk around the rim.

I had a very narrow escape because if the caulk had completely failed, the boat would have flooded very quickly. The threaded stem of the valve had completely sheared from the valve body, and I could see the end of the bung in the through-hull stem – and it was dry.

I still don’t know why that stem parted, because it was completely encased in the hard caulk from the hull up to the valve to stop any possible vibration. The stem was bronze like the valve, so no dissimilar metal fatigue had occurred; it had just snapped.

A wooden block screwed onto the hull of a boat after a failed seacock

The wooden block that Roger glued and screwed to the top of the opening to form a seal inside the boat. Credit: Roger Hughes

With hindsight, if I’d known the size of the bung that was needed it would have been possible to yank the fractured valve out of the way and quickly hammer the bung in from the inside – no doubt with a soaking – but it would have stopped the leak. The pressure of water would only be just over one pound per square inch at that level, so the bung would have held from the inside. It is a very good policy to have a bung of the correct size tied to every seacock on your boat, just in case.

With the panic over the next question was, what to do now? I didn’t feel entirely comfortable leaving the solitary bung in place for long, although these specially tapered bungs tend to wedge very firmly in place. Then I had a brainwave: around the outside of the valve stem is a wide, circular, half-inch-thick wooden backing plate, bonded to the hull to give extra thickness to screw a seacock together.

I found a block of 2½in square teak which was an inch thick. I drilled a hole in each corner, then coated it liberally with waterproof wood glue and screwed it down on top of the valve opening.

Waterproof seal

Once dry, it forms a waterproof seal and I was confident that with the bung in place and the wood block securely screwed and glued on the inside, Britannia would be safe until she could be lifted out and fitted with a new seacock. I also transferred the AC inlet pipe to the generator seacock next to it, which enabled the AC to be switched on until I could get it repaired. I never use the generator while on shore power, but I definitely do need the air conditioning.

A backing plate on a boat

Backing plates help distribute load, preventing stress cracking around the valve area. Credit: Roger Hughes

When I eventually had Britannia lifted I had to chisel the wood block off the backing plate to fit a new seacock. I also closely inspected all of the other nine underwater hull fittings both inside and out.

There is now a bung of the correct size tied to every seacock and I earnestly suggest to readers that they do the same. It is a very small cost to assuage a possible very expensive seacock leak. I am also thankful that it at least happened alongside a pontoon where a diver was quickly available and not in the middle of the ocean. I suppose you should always be grateful for small mercies with boats.

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