Closed while unattended is the only way I do it. Takes but a few seconds but can save a lot should one fail.

The primary reason to close the seacocks, in my understanding, has little to do with seacock failure. The ways a seacock can fail when open are not hugely different from the ways a seacock can fail when close. Furthermore it does nothing to stop thru-hull failure, because if the thru-hull itself leaks, it may be around the seacock and not through it.

Your thru-hulls without a seacock (e.g., the ones around the sounder) are just as likely to leak as the thru-hulls that have a seacock, and I've heard very well salted sailors swear that constantly opening and closing your seacocks is a terrible thing to do for the longevity of the thru-hull seal. This is highly controversial.

The reason you are closing the seacocks is because of potential failure in an upstream component that is also below the waterline. For example, if you leave the sink drain seacock and a hose or joint sitting below the waterline fails, then you're going to have a huge leak. I've seen this happen too.

The engine thru hull is a big pain. The galley is not too bad, but I've checked all the hoses and clamps. They seem OK and it's hard to imagine they would pop off while the boat is at dock.

The head seacock will fill the sink to overflowing any time I'm on a starboard tack and pounding upwind. I've gotten a lot of water in the boat from that one, to the point of taking out the fresh water pump because the bilge water was splashing above the floor boards and among the fresh water pump, battery charger, and air conditioner. Now I close it any time the head is not being used.

I think a more important issue is to check fittings, tightness of clamps, and general hose conditions.

Always closed if I leave the boat more than an hour.
John Meyer
Hilbre 2135

Well as usual I am the oddball in the group. I close my seacocks in the fall, if I am leaving the boat for a couple months during the winter; otherwise they stay open. I figure that if I can trust ('trust, but verify') my systems in the ocean, I can sure as hell trust them at the dock.

I do the same as you Larry..I believe in always doing things the same way when running multiple systems,like any boat.It makes for rapid and consistent departure and start up routines.the KISS principle.

I'm with Larry & Greig. 28 years and I only ever close the engine one. So far, so good.:D

Mike

I rarely close mine; so far, so good. It's only been a few months.

We always close them when leaving the boat. I lube them in the fall as part of lay up, I leave them open in winter on the hard. I was using lanocote but the chandlery we deal with told me there is now a lube specifically for them from Forespar called Marelube I am going to use that this year.

Other than when laying up I exercise all thru hulls monthly. I close all thru hulls when on the hard so no tiny critters or insects including bees/wasps etc can find their way into the boat and nest. As a further precaution, I even plug the holes to the closed thru hulls. But, keep in mind, Hilbre is laid up in a warm climate.
John Meyer

We always close all of them when we leave the boat for any significant stretch, say more than a day. I can't agree with Larry, which is rare. If there's a failure while I'm aboard, at least I may be able to do something about it. If it happens when I'm away, the boat will sink. As has been said, they only protect from the valve inward, but there's a lot more to go wrong inboard of the valve - hoses, clamps, fittings, pumps, gaskets, strainers, fixtures - so why not limit the possible areas of failure to just the through hull and the seacock, neither of which is likely to give. I also believe that using those seacocks more often will keep them working and if they are getting stuck, stiff, or jammed, or are not doing their job, you will notice it and correct it before it becomes catastrophic. Nothing like discovering the seacock is frozen just when the hose it is supposed to be attached to comes off, and you need to close it now! We have a large printed warning saying they are closed, which is the last thing we leave on the galley sink cover when we lock up - it is the first thing we see when we re-open the companionway. Been working for over thirty years.

We have a selection of plugs in the cupboard just ahead of the nav station, along with other emergency gear (flares, flashlights, etc.). They are wooden ones we've had forever, but I like the newer plastic ones and plan to get a couple.

They're made by Forespar, although there may be others similar. This is what I mean, from Westmarine or almost any chandler

My spin on this question is whenever I leave the boat for the day or weekend, I close all the valves. Sure the thru hull can leak and break down. I've had one in a previous boat when I turned the valve it broke off at the thru hull fitting. Fortunately I was on the hard at the time. I carry a set of wooden plugs and recall one time seeing a boat that used a beercan to stuff a hole.
Back to why I shut the valves. Normally sitting in calm water you may not pop a hose. Im on a mooring in 54' of water and occasionally it gets a little rough and the boat is bouncing. It is one thing when on the boat but it is another when it is unattended, so I don't gamble. I have a cycle counter on my bilgepump to forewarn me of excessive water. This gives me a chance to start looking for any problems.
Just my two cents.

I was told by an old salt who had sailed for more than three decades all over the world to keep a (what he called a bung) by each seacock and thru hull. So, I purchased the wooden ones and placed an screw eyelet toward the top of the large end. Then, I attached a short piece of line to it and then secured the other end of the line around the thru hull somewhere. That way, one of them is always within a few inches. FWIW

The big risk with the Forespar OEM marelon seacocks is snapping the handle off and having the guts come out. You don't have a nice clean hole to shove a wood plug down into, it will be on the side and can be hard to get at. Driving a plug in will likely just shatter whatever is left. Probably the orange foamy plug shown earlier in this thread would be a better fit. I really dislike these seacocks, as has been discussed many times on forums everywhere, even just having the screw holding the handle come loose will start a leak. So I think exercising them can minimize the chances of gunk build up causing friction and a broken handle causing an OMG moment. Changing them to non-OEM units is not as simple as it looks, on our boat the bases and thru hull inserts are well glued in and it will be a destructive job to say the least. I changed the 1.5" macerator one and it was extensive work even in an easy to get at spot. The others are far worse.

I'm with the "always close when you leave the boat" crowd.
Indeed, an incident while cruising last week re-affirmed my belief in this.
One of our crew had use the shower while we were moored, and left the seacock for the shower sump drain open. A half hour later, just as we were about to dingy into town, another crew went to retrieve something from the head and yelled out that the floor was totally flooded. Turned out that the vacuum breaker for the shower sump discharge was clogged, so the hose was slowly siphoning sea water back into the shower sump. But it took some time for this to manifest - and had we left slightly earlier without closing the seacock, we might have returned to see our mast sticking out of the water....