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Old 26-06-2016, 16:08   #1
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Servicing seacocks, plugging thru-hulls, when the boat is in the water

I have older, cone-type seacocks. I want to service them without hauling out the boat. The excellent description on the Compass Marine site explains how to use valve grinding compound to lap the cone and body while the seacock is in place. To do this, the seacock must be kept dry. My plan has been to put a plug in the thru-hulls from the outside of the hull, in the water, or otherwise stop water from coming into the thru-hulls. Then, I would suck the remaining water out of each seacock from inside the boat, disassemble the seacock, lap it, reassemble it, and re-open the thru-hull..

I have had modest success trying to plug the thru-hulls. The challenge has been caused by the ridges inside the thru-hulls. The bores of the thru-hulls are not smooth. Thus, a simple conical or cylindrical plug or cork, like a typical boat drain plug or emergency wood plug, will not work. Lacking a tight seal, some water will pass through, making the seacock lapping process fail. Any water entering will wash away the valve grinding compound.

I have made plugs out of Dum Dum (Duct Seal) and closed-cell foam. The water flow was reduced to a trickle but did not stop. I am wondering if there is some other material that might make a tight seal against the sharp edges of the ridges inside the thru-hulls.

I also have thought about, but not tried, installing some barriers that could cover over the thru-hulls on the outside. Barriers would also keep water out of the thru-hulls that have external strainers, those that will not admit a plug. But coming up with a suitable barrier has been a challenge. I believe that a simple sheet of plastic or sailcloth would slide off outside as soon as the seacock was disassembled inside because air would be admitted on the inside, eliminating the water pressure holding the sheet in place. I believe that a toilet plunger would not form a tight seal against the bottom which is not perfectly smooth. Besides, it is hard to find someone who would stay underwater holding the toilet plunger in place while the seacock is being serviced. I wonder whether there is a temporary adhesive that would adhere underwater, hold a plastic sheet in place, form a watertight seal around the perimeter of the sheet, and not damage the bottom paint when removed.

Any ideas or experience on keeping ALL water from entering a thru-hull when a boat is in the water?
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Old 26-06-2016, 16:25   #2
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Re: Servicing seacocks, plugging thru-hulls, when the boat is in the water

Simply put, you are asking for a "sank at the dock" insurance incident. Any failure means a flood that no bilge pump can handle. You must have a scheduled haul ahead of you somewhere - replace anodes, bottom paint, get the barnacles off the prop, whatever. Messing with a shaky plug is not where you want to be with such serious consequences. You want to be able to methodiucally pull each one of your seacocks and sand them smooth, then grease and rebuild, without worrying that when you turn around you're going to see your boat sinking. I've got a big seacock that needs remounting and a cleaning just like yours. In August, the boat comes out for sandblasting and painting, and all those jobs (weld the seacock mount, clean the seacock, change the anodes) will get done while it's out.
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Old 26-06-2016, 16:36   #3
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Re: Servicing seacocks, plugging thru-hulls, when the boat is in the water

"I believe that a simple sheet of plastic or sailcloth would slide off outside as soon as the seacock was disassembled inside because air would be admitted on the inside, eliminating the water pressure holding the sheet in place."

I pulled the above paragraph out of your post.

Your logic here is flawed, it is the water pressure keeping the fothering material against the hull. However this is also doomed to leak like all the other attempts.

If you're hell bent on doing this In The water I think your best bet would be the expanding plugs that plumbers use to test plumbing installations. They may even have enough wiggle room on the rubber to seal completely despite the ears inside if the mushroom.


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Old 26-06-2016, 16:42   #4
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Re: Servicing seacocks, plugging thru-hulls, when the boat is in the water

Why are you in a hurry to get this done? If they are leaking a little, just keep your automatic bilge pumps working and fix the seacocks next time you haul.

If you are determined to do it with the boat in the water, I've heard of people using the wax ring that is used to mount toilets on. Just work it in your hands until it's pliable and shove it in.
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Old 26-06-2016, 18:42   #5
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Re: Servicing seacocks, plugging thru-hulls, when the boat is in the water

+1 on the toilet wax ring.
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Old 27-06-2016, 09:06   #6
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Re: Servicing seacocks, plugging thru-hulls, when the boat is in the water

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+1 on the toilet wax ring.

Ditto on the wax ring cheap and easy to use.
Plugs small holes don't know about large ones though. Australian have the Bung. It looks like a umbrella and is rubber. You slip it through the sea cock outside and pull it back through when done. this is a good way to remove the sea cock entirely and replace it. check those thru hulls though.
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Old 27-06-2016, 09:25   #7
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Re: Servicing seacocks, plugging thru-hulls, when the boat is in the water

I have been thinking about the same issue as I need to replace a cut off valve down stream of my valveless through hull. It seems to me that, if not moving or in strong current flow, water pressure would force a good seal using any flexible material such as rubber gasket. However, I'm holding off until I can recruit a helper who can jump overboard and replace the patch or drive a plug if there is a problem in the middle of the process. I guess my trust in theory is just too limited.
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Old 27-06-2016, 09:32   #8
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Re: Servicing seacocks, plugging thru-hulls, when the boat is in the water

Use a bucket with foam seal at the top, it works great, and gives you plenty of time, put the new transducer or seacock or whatever will not fit through the hole in the bucket before you press it against the hull. An air bag or rope can hold it against the hull while you install it, but a much easier method is to provide a slow leak from a slightly removed transducer, etc, it will grab it and hold it almost immediately after you push the bucket against the hull and it seals. Also the water pressure can collapse the bucket so it would be good to reinforce it. It amazed me that 18 inches of depth could have this much force. The pictures don't show it but the final version had a wood cross about 1/2 way down inside the 5 gal bucket to keep it from collapsing. You can suck all the water out of the bucket using a vacuum cleaner through the hole. You can see what I tried and what worked and didn't work on my website. I do this all single handed. Click on the repair at sea link below.

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Old 27-06-2016, 10:06   #9
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Re: Servicing seacocks, plugging thru-hulls, when the boat is in the water

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Originally Posted by jheldatksuedu View Post
Use a bucket with foam seal at the top, it works great, and gives you plenty of time, put the new transducer or seacock or whatever will not fit through the hole in the bucket before you press it against the hull. An air bag or rope can hold it against the hull while you install it, but a much easier method is to provide a slow leak from a slightly removed transducer, etc, it will grab it and hold it almost immediately after you push the bucket against the hull and it seals. Also the water pressure can collapse the bucket so it would be good to reinforce it. It amazed me that 18 inches of depth could have this much force. The pictures don't show it but the final version had a wood cross about 1/2 way down inside the 5 gal bucket to keep it from collapsing. You can suck all the water out of the bucket using a vacuum cleaner through the hole. You can see what I tried and what worked and didn't work on my website. I do this all single handed. Click on the repair at sea link below.

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Old 27-06-2016, 10:20   #10
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Re: Servicing seacocks, plugging thru-hulls, when the boat is in the water

Google 'seabung' to see how to plug the thru hull.
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Old 27-06-2016, 11:01   #11
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Re: Servicing seacocks, plugging thru-hulls, when the boat is in the water

On the thru hulls without stainers use plumbers putty around the wood plug. you might want to shorten the skinny end a little so it doesn't hit the valve or any other obstruction. the ones with the grills? clean the surrounding surface and put a thick ring of plumbers putty at the edge of thru hull and press plastic sheeting to it, leave the seacock open or have someone open it as you stick it on. don't leave a lot of excess sheeting around the area as wave and/or current would cause it to move. the plumbers putty can be removed and re-used easily. when using the plug you will have plenty of time to do the job....even walk away and eat lunch. when using the sheet start and Finnish the job in one sitting...if needed reassemble the valve un-lapped and come back. I just did two seacocks last week.

as far as "no bilge pump can keep up..."? My 3800 rule pump is faster than a 2 inch hole 16 inches or so below the water line. found this out whilst replacing the galley sink thru hull. I did need a hand tho to remove and install it. doesn't leak either...5200 cures in the water. gotta use a lot and shove it in quick. makes a bit of a mess, but can be cleaned up, fairly easily. Need air too...thank God for my hooka;-) if you have everything ready...mentaly go through the sequence a few times to make sure everything is ready...take your time and don't rush, it goes pretty quick. rushing will take longer;-) the pump came on and cycled off once. I didn't even really need it to do that as I only took on about 5 gallons or so. went back under to remove the plug after attaching the valve to the thru hull. Both people will have to be competent for the job, as you can't give instruction to one another whilst one is underwater and the other in the bilge ;-)

I just can't get my submersible VHF to be understood from underwater....hmmmf...imagine that? have to work on those telepathy skills. Any Help there?

Don't sweat the water ingress as it won't be coming in all that long. worst comes to worst...like you broke the thru hull... plug it till you get another one to replace it. Look the job over and be sure you have a back up plan....ie...extra plug and topped off batteries.

good luck
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Old 27-06-2016, 11:26   #12
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Re: Servicing seacocks, plugging thru-hulls, when the boat is in the water

Haul and replace. Attempting to do this in the water, on the cheap, for the first time is asking for trouble.

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Old 27-06-2016, 11:37   #13
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Re: Servicing seacocks, plugging thru-hulls, when the boat is in the water

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Haul and replace. Attempting to do this in the water, on the cheap, for the first time is asking for trouble.

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First times are generally screw ups. Btdt. But it might provide some entertainment at the yacht club. " How did that boat sink?" Besides, you might just want to replace the entire set up with a better sea cock situation. Haul out.
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Old 27-06-2016, 12:22   #14
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Re: Servicing seacocks, plugging thru-hulls, when the boat is in the water

For each of us, there are acceptable risks and unacceptable risks, and risks can move from one category to the other dependent on the situation.

One reason why the captain gets command responsibility pay.
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Old 27-06-2016, 13:49   #15
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Re: siezed seacocks,

I have been trying to figure out just how to post my question. Have not
used this since 2013.
I have never had problems with opening seacocks. Never thought of on trying such in dry dock. Now, in water and can not open head seacocks. Used WD 40 to no avail. And then 104 lbs and not mechanically inclined. Help.
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