Underwater putty recommendations - rather important!

Dipper

Dipper

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I fitted a new Marelon seacock to my heads inlet and have launched my boat today. Unfortunately, the seacock seems to be leaking around the thread. Either I haven't tightened it up enough (it's only supposed to be hand tight) or I didn't cut enough off the end of the skin fitting for it to seat properly. The instructions say to seal the thread with PTFE tape which I did. If I can't tighten it any further I will need to do something to stem the leak. It let in 2 litres in 6 hours so its not an inconsequential weep but I'm not going to sink in the next few days either.

One solution would be to use underwater putty to seal the leak even if this means that the next time I need to remove the fitting I have to destroy it. Can anyone recommend something that has worked for them?

Many thanks in advance.
 
I used yellow/black standard milliput on a leaking transducer last weekend and it worked very well. Reacted perfectly with water too. Would recommend that.
 
If your sescock is a straight through 1/4 turn valve....
I saw a device on Dragons' Den for seacock maintainance while at sea. Basically a rubber circle on the end of a stick. get it ready, close the seacock and take the pipe off the top. Open the seacock and shove the thing through to outside and let it sit back against the hull, sealing the inlet. Now you can refit the valve.

A home built solution would be an inflatable stent made from a bicycle inner tube. Use it in similar fashion.
 
If you can get hold of Loctite 55, that will do the trick. It's PTFE cord and can be used wet and dry, you can loosen the seacock, rap the stuff on and then re tighten the sea cock. Don't ask how I know!

It is a bit like dental floss and works on water and gas, I got mine from Plumbase.
 
VicMallows said:
It is not at all clear whether your leak is where a skin fitting passes through the hull, or where a valve is attached to a skin fitting. I suggest you clarify if you want meaningful suggestions.
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I think it's leaking around the thread. With the Marelon fitting, the skin fitting is stuck into the hull with Sikaflex 291. There is no backing nut. The threaded part of the fitting is cut to length as it can fit a wide range of hull thicknesses then they advise using PTFE tape on the thread. The seacock is screwed onto the thread hand tight until it fits flush onto the backing pad and secured to the backing pad with two screws so that it can't turn. I don't think the skin fitting is leaking as I used a generous dollop of Sikaflex to get a good seal. The leak appears to be coming from where the seacock touches the backing pad but until I dismantle the heads, I won't know for sure.
 
+1 for the loctite 55, if its not your through hull leaking then this stuff is what you need, read the instructions and don't be tempted to wrap on more than recommended.

Turnnidge said:
If you can get hold of Loctite 55, that will do the trick. It's PTFE cord and can be used wet and dry, you can loosen the seacock, rap the stuff on and then re tighten the sea cock. Don't ask how I know!

It is a bit like dental floss and works on water and gas, I got mine from Plumbase.
Click to expand...
 
Dipper said:
I think it's leaking around the thread. With the Marelon fitting, the skin fitting is stuck into the hull with Sikaflex 291. There is no backing nut. The threaded part of the fitting is cut to length as it can fit a wide range of hull thicknesses then they advise using PTFE tape on the thread. The seacock is screwed onto the thread hand tight until it fits flush onto the backing pad and secured to the backing pad with two screws so that it can't turn. I don't think the skin fitting is leaking as I used a generous dollop of Sikaflex to get a good seal. The leak appears to be coming from where the seacock touches the backing pad but until I dismantle the heads, I won't know for sure.
Click to expand...

This sort of thing then??? ..... No mention of tape though just Sikaflex!
Probably your tape has prevented you screwing it down onto the backing pad properly!




Dry out remove and redo .... anything else is a bodge and could leak again!


You can always trust a man with a good beard



.
 
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If you can reach the fitting from outside, have a swim and push in a softwood bung, or one of those soft rubber cones. You can then unscrew the seacock. Shorten the through hull if you need to but do not use PTFE tape. The best stuff to seal threaded plastic fittings is Loctite 5331.

EDIT Loctite 5331 is purpose made to seal plastic fittings. http://www.loctite.co.uk/loctite-4087.htm?nodeid=8802626764801 I used it on all of my Tru Design fittings.
 
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Norman_E said:
If you can reach the fitting from outside, have a swim and push in a softwood bung, or one of those soft rubber cones. You can then unscrew the seacock. Shorten the through hull if you need to but do not use PTFE tape. The best stuff to seal threaded plastic fittings is Loctite 5331.

EDIT Loctite 5331 is purpose made to seal plastic fittings. http://www.loctite.co.uk/loctite-4087.htm?nodeid=8802626764801 I used it on all of my Tru Design fittings.
Click to expand...

Thanks for all the suggestions Lots to think about.

It's a bit strange that their written instructions mention using Teflon tape on the threads. See here: http://www.forespar.com/pdf/install/F122-904000-install-flange-mounting-seacock.pdf

I wish it was easier to dry out in Portland Harbour but the tides are so pathetic that it doesn't make it that easy (and I've never tried it before). The problem with seacocks is that they are difficult to test before you go into the water.
 
If you want to remove the seacock, remember that it has a bung in the handle that can be used (from outside; you'll have to get wet!) to seal the skin fitting.

I am about to fit a couple of these & from my understanding of how they work it seems important that the inside hull surface is flat and parallel to the (flat) outside surface. My backing blocks inside the hull are a bit rough & ready, so I plan to sand & fill them first. If your backing blocks are not flat or parallel to the outside surface of the hull you may not get a good seal when you tighten up your fitting. You may find that the leak is reduced by loosening the fitting a little. If so, I guess your backing blocks may need some work.
 
Dipper said:
Thanks for all the suggestions Lots to think about.

It's a bit strange that their written instructions mention using Teflon tape on the threads. See here: http://www.forespar.com/pdf/install/F122-904000-install-flange-mounting-seacock.pdf

I wish it was easier to dry out in Portland Harbour but the tides are so pathetic that it doesn't make it that easy (and I've never tried it before). The problem with seacocks is that they are difficult to test before you go into the water.
Click to expand...

Tru Design also recommend Teflon tape, but the threads are a pretty loose fit and the surveyor I know gave me the end of a tube of Loctite 5331 which he had used on another boat. I had tried Teflon tape and found that it did not give a reliable seal, but the Loctite did.

If your Marelon sea cocks have a seal to fit from the outside you don't need to dry out as a swim should enable you to fit it. I have dealt with a blocked fitting before by swimming and inserting wire to clear it, so putting in a bung should be easy enough, mind you that was in much warmer water than you have this time of year in the UK.
 
daveyw said:
Tec7 from most builders merchants and B&Q for about £8. Take a swim and apply it under water. Sticks like the proverbial!
Click to expand...

The OP does not believe its leaking between the skin fitting and the hull but between the skin fitting and the valve
 
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