Fitting a new Tru Design through-hull between tides - sealant questions

Poey50

Poey50

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I'm thinking of fitting a 38mm Tru Design composite through hull + ball valve + hosetail + hose as part of a new gravity holding tank system and, to add to the excitement, I would like to do it between tides. This would be a new through-hull, not a replacement.

Tru Design recommend three different one-part polyurethane sealant / adhesives (Silkaflex 291i being one), all of which are said to be just cured enough to attach ball valve, hose etc. after 2 hours. But it's not absolutely clear to me that the curing will continue happily once the water returns after another couple of hours. Will it?

I have seen recommendations (not from Tru Design) to use a polysulphide sealant in these circumstances to cure underwater but the ones i have looked at seem to have a longer cure time than the polyurethane ones and no indication of how quickly the sealant would be firm enough to fit the valve etc. Someone here will know.

So advice welcome on both the polyurethane and polysulphide issues as well as any other dire warnings of catastrophe.
 
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I fitted a new stainless steel heads seacock to my steel hull below the waterline between tides using sikaflex and all still OK 2 years later.

You just need to prevent movement of the sikaflex joint while tightening the in my case stainless steel ball valve to the skin fitting.
 
Poey50 said:
I'm thinking of fitting a 38mm Tru Design composite through hull + ball valve + hosetail + hose as part of a new gravity holding tank system and, to add to the excitement, I would like to do it between tides. This would be a new through-hull, not a replacement.

Tru Design recommend three different one-part polyurethane sealant / adhesives (Silkaflex 291i being one), all of which are said to be just cured enough to attach ball valve, hose etc. after 2 hours. But it's not absolutely clear to me that the curing will continue happily once the water returns after another couple of hours. Will it?

I have seen recommendations (not from Tru Design) to use a polysulphide sealant in these circumstances to cure underwater but the ones i have looked at seem to have a longer cure time than the polyurethane ones and no indication of how quickly the sealant would be firm enough to fit the valve etc. Someone here will know.

So advice welcome on both the polyurethane and polysulphide issues as well as any other dire warnings of catastrophe.
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Just a thought. I take it you will be making a new hole using a hole saw. Just wondering what type of layup your hull is.
I have always sealed the end grain with epoxy . Particularly foam sandwich.

Polysulphide is not easy to find now and has largely been superseded by products like CT1 .
 
Poey50 said:
I'm thinking of fitting a 38mm Tru Design composite through hull + ball valve + hosetail + hose as part of a new gravity holding tank system and, to add to the excitement, I would like to do it between tides. This would be a new through-hull, not a replacement.

Tru Design recommend three different one-part polyurethane sealant / adhesives (Silkaflex 291i being one), all of which are said to be just cured enough to attach ball valve, hose etc. after 2 hours. But it's not absolutely clear to me that the curing will continue happily once the water returns after another couple of hours. Will it?

I have seen recommendations (not from Tru Design) to use a polysulphide sealant in these circumstances to cure underwater but the ones i have looked at seem to have a longer cure time than the polyurethane ones and no indication of how quickly the sealant would be firm enough to fit the valve etc. Someone here will know.

So advice welcome on both the polyurethane and polysulphide issues as well as any other dire warnings of catastrophe.
Click to expand...

I fitted mine with arbomast br a few years back having done the same thing. The other option was to fibreglass it in but gave that a miss.
 
Poey50 said:
Tru Design recommend three different one-part polyurethane sealant / adhesives (Silkaflex 291i being one), all of which are said to be just cured enough to attach ball valve, hose etc. after 2 hours. But it's not absolutely clear to me that the curing will continue happily once the water returns after another couple of hours. Will it?.
Click to expand...

Polyurethane sealants and adhesives are, in fact two-pack. The second "pack" is ambient moisture, of which there will be no shortage when the tide comes in.
 
LONG_KEELER said:
Just a thought. I take it you will be making a new hole using a hole saw. Just wondering what type of layup your hull is.
I have always sealed the end grain with epoxy .
Click to expand...

Yes I was planning to seal the end grain around the hole with some fast-setting two-part Araldite epoxy.
 
I too used 291i. When they were fitted the yacht surveyor who helped me sealed them with 291i and tightened the inner nut gently, tightening it further once the sealant had started to cure. He said that was important because fully tightening immediately will squeeze out most of the sealant and could result in a poor seal. Working between tides will give you enough time to get a decent seal if you get the hole done as soon as the tide allows. On the second low tide you can trim away any excess sealant.
I think that Tru Design suggest sealing the ball valve to the through hull with PTFE tape. I found that the threads are a pretty loose fit and would have needed a lot of tape. My surveyor friend used a tube of this stuff to seal them. https://www.bearingsrus.co.uk/l5331...gNnpFEu-dn_L5BaCHakydNnFOAjzAd1hoCvpEQAvD_BwE It made a good seal and allowed the ball valve handles to be correctly aligned.
 
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Norman_E said:
I too used 291i. When they were fitted the yacht surveyor who helped me sealed them with 291i and tightened the inner nut gently, tightening it further once the sealant had started to cure. He said that was important because fully tightening immediately will squeeze out most of the sealant and could result in a poor seal. Working between tides will give you enough time to get a decent seal if you get the hole done as soon as the tide allows. On the second low tide you can trim away any excess sealant.
I think that Tru Design suggest sealing the ball valve to the through hull with PTFE tape. I found that the threads are a pretty loose fit and would have needed a lot of tape. My surveyor friend used a tube of this stuff to seal them. https://www.bearingsrus.co.uk/l5331...gNnpFEu-dn_L5BaCHakydNnFOAjzAd1hoCvpEQAvD_BwE It made a good seal and allowed the ball valve handles to be correctly aligned.
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Thank you. Yes, Tru Design recommend tightening of the through-hull nut 2 hours after application of the sealant. They now recommend various sealants on the thread when attaching the ball valve. These include the Loctite 5331 that your surveyor friend used. That seems particularly good as hoses can be fitted as soon as 10 minutes after application so that is the one I will probably go with.

One issue that I can't quite get my head around is how to ensure that the handle of the ball valve is the correct orientation when using a load bearing collar since, with the through-hull fixed, the height of the collar determines how much the ball valve can be tightened down. Probably the base of the valve doesn't have to be a totally snug fit against the collar as the valve is held by the sealant.

Thanks, by the way, to all who have offered suggestions - very helpful.
 
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I must admit that I did not fit collars to mine, but my suggestion is that after tightening the nut on the through hull, put the collar in place and do a dry run with the ball valve to see which way it faces. You could then remove the collar and thin it as much as required by rubbing it on a piece of coarse abrasive paper on a flat board. An alternative would be to cut some suitable sized "washers" from different thicknesses of this stuff, and put one of the right thickness between collar and ball valve. https://slatersplastikard.com/plastikard/standardPlastikard.php
Another possibility is to put the 5331 onto the threads but a bead of 291i onto the top of the collar and screw the ball valve on until it faces the right way and has squeezed out most of the 291i, though I am not really sure if this is actually as good an idea as the first suggestion or the plastikard washers.
 
Norman_E said:
I must admit that I did not fit collars to mine, but my suggestion is that after tightening the nut on the through hull, put the collar in place and do a dry run with the ball valve to see which way it faces. You could then remove the collar and thin it as much as required by rubbing it on a piece of coarse abrasive paper on a flat board. An alternative would be to cut some suitable sized "washers" from different thicknesses of this stuff, and put one of the right thickness between collar and ball valve. https://slatersplastikard.com/plastikard/standardPlastikard.php
Another possibility is to put the 5331 onto the threads but a bead of 291i onto the top of the collar and screw the ball valve on until it faces the right way and has squeezed out most of the 291i, though I am not really sure if this is actually as good an idea as the first suggestion or the plastikard washers.
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Good suggestions - I'd not heard of Plasikard which could instead go under the collar. Thanks again.
 
For completeness - current plan for anyone willing to check my homework or anyone thinking of fitting a new through-hull for Tru Design 38mm ID through-hull + collar + ball valve + hosetail between tides or lifted out.

i. INSIDE Final check on location.
ii. Mark location.
iii. OUTSIDE When water recedes ensure hull area is dry
iv. INSIDE Drill pilot hole 3mm diam.
v. Using hole saw of 49mm to drill hole.
vi. OUTSIDE Scrape off antifouling under flange, roughen GRP.
vii. Seal edges of hole with fast drying Araldite epoxy.
viii. Dry fit through-hull – hold in place outside with tape.
ix. INSIDE Put on rubber seal + nut and dry fit. Measure from nut to end of fitting. Max length is 32mm, min is 22mm.
x. Cut with hacksaw at 31mm. Remove any internal rough edges with small file.
xi. OUTSIDE Smear 291i on flange of through hull and partway up thread but no higher than thickness of hull (i.e. not on thread under nut).
xii. With fitting tool inserted push through-hull into position and hold with tape.
xiii. INSIDE Holding fitting tool, put on washer and nut and do up finger tight.
xiv. OUTSIDE With angled putty tool or similar take off surplus sealant and blend in the edges. Touch-up anti-fouling (but not cover sealant).
xv. INSIDE After two hours minimum tighten up the nut to 15 foot-lb (don’t over-tighten).
xvi. Locate bearing collar over through-hull and dry-fit the valve and ensure that the handle is in the correct position. If not, cut suitable sizes of Plastikard to dry-fit under collar.
xvii. Loctite 5331 on through-hull threads. Tighten valve to 12 ft/lbs with ball valve spanner ensuring handle is in correct position.
xviii. Leave a minimum of ten minutes. With ball valve closed, hull should now be watertight. (Cross fingers, utter pointless prayer etc.). Check for leaks when water returns.
xix. Smear Sikaflex 291i on threads of 120 degree hosetail and ensure it positions correctly.
xx. Leave two hours and attach hose.
 
Good luck. Maybe it’s just me being an old maid but i would be thinking of lots of fall back positions too. ie what happens if…
Big petrol water pump, large tarp etc etc…
 
Malabarista said:
Good luck. Maybe it’s just me being an old maid but i would be thinking of lots of fall back positions too. ie what happens if…
Big petrol water pump, large tarp etc etc…
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I think the biggest risk is falling off the slippery ladder attached to Itchenor drying posts and knocking myself out after drilling the hole. So I'm going to take my own ladder. Other than that there's a bung, hammer, mechanical bilge pump, and a nearby boat lift.
 
Norman_E said:
Poey50. Item xix Sikaflex 5331 not 291i on threads of hosetail.
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Thanks for checking. I did ponder that one myself. The downside of the Loctite 5331 is the low strength of the bond. No problem with the ball valve on the through-hull as it is tightened down onto the bearing collar and the fast curing makes it suitable for this job. I would probably use it for the hosetail if it was a straight one, since that could be tightened down also, but it is a 120 degree one which needs a particular orientation and may not be tightened unless I'm lucky or can arrange some packing. So I think the Silka 291i would be stronger and the fact it takes two hours before I can put the hose on is no problem since the hull will be watertight at that point.
 
I have 90 degree hosetails fitted with 5331, and its no problem at all. 5331 does allow you to adjust the position a bit even after curing for a few hours. Method of application is to put three axial beads of it at 120 degrees on the male threads. then screw the fittings together.
 
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