Keel/hull seal advice sought

[JamieB]

We have a slow leak coming from under a GRP ‘step’ where our furthest aft keel bolt is located (pic attached). We had the keel remover three years ago to inspect keel bolts and re-bed the hull/keel joint. It was found to be in good shape and a load of new sealant was applied (after removing old) before bolts were torqued to correct load. It appears this is a slow leak coming through where the trailing edge of the keel meets the hull.

I’ve been thinking about how to resolve this - and am clearly not keen to drop the keel again unnecessarily. One idea I had was to install a vacuum bag around the offending spot in the bilge and vacuum epoxy through from the outside using a second bag to fill the void. I was assuming an initial pre-vaccum could help remove any residual moisture.

Does anyone have any thoughts on this as a concept? Any thoughts greatly appreciated.

 

[ducked]

Sounds like a plan, but I dunno how compatible infused epoxy will be with whatever sealant is already there, and there is the obvious snag that if it doesn't work it will probably make dissasembly to fix more difficult.

Was flexible sealant used to bed the refitted keel? I understand this is now contraindicated in favor of gluing it on with epoxy, though I daresay there is argument.

If you try this, perhaps remove all that stuff around the stud, and also make your first infusion something like acetone, which should help clean and dry and give you some pre-testing of the procedure. Then I suppose you;ll want as slow a catalyst as possible.

OTOH IF you only want a sealant, rather than physically reinforcing the keel joint with glue, perhaps something else that doesn't use catalyst might be more suitable. Maybe an alkyd resin, though I'm not sure how that polymerises, maybe by atmospheric oxygen?

EDIT Apparently its by initial autooxidation followed by atmospheric, (caveat:AI summary) so it might stay liquid inside the keel for a long time but surface skin quite quickly. This MIGHT be good enough for containment.

If you go in the other direction, gravity would be your friend, but you would run the risk of sealing the leak into the bilge while the keel joint remained open, potentially compromising your keel bolt(s)

 

[lustyd]

Don’t put acetone in, you’ll damage the hull!

I wouldn’t use epoxy, any flex and it’ll break leaving you with a messy leak rather than just a leak.

Assuming something like Sika has been used then in theory tightening the bolts should stop it.

Are you absolutely certain the water is coming inwards?

 

[JamieB]

Sounds like a plan, but I dunno how compatible infused epoxy will be with whatever sealant is already there, and there is the obvious snag that if it doesn't work it will probably make dissasembly to fix more difficult.

Was flexible sealant used to bed the refitted keel? I understand this is now contraindicated in favor of gluing it on with epoxy, though I daresay there is argument.

If you try this, perhaps remove all that stuff around the stud, and also make your first infusion something like acetone, which should help clean and dry and give you some pre-testing of the procedure. Then I suppose you;ll want as slow a catalyst as possible.

OTOH IF you only want a sealant, rather than physically reinforcing the keel joint with glue, perhaps something else that doesn't use catalyst might be more suitable. Maybe an alkyd resin, though I'm not sure how that polymerises, maybe by atmospheric oxygen?

EDIT Apparently its by initial autooxidation followed by atmospheric, (caveat:AI summary) so it might stay liquid inside the keel for a long time but surface skin quite quickly. This MIGHT be good enough for containment.

If you go in the other direction, gravity would be your friend, but you would run the risk of sealing the leak into the bilge while the keel joint remained open, potentially compromising your keel bolt(s)

Thanks for the ideas and interesting thought re alkyd. I've had another idea and am going to experiment in the garage to see how suggestable Sika is to being vacuumed.

 

[JamieB]

Don’t put acetone in, you’ll damage the hull!

I wouldn’t use epoxy, any flex and it’ll break leaving you with a messy leak rather than just a leak.

Assuming something like Sika has been used then in theory tightening the bolts should stop it.

Are you absolutely certain the water is coming inwards?

Thank you. Yes it's defo inward. I will also try and tighten the bold once she's out of the water. I've had another idea and am going to experiment in the garage to see how suggestable Sika is to being vacuumed - that may allow me to fill the tiny area its getting through. It's odd because she was so recently re-bedded with plenty of suiatble flexible sealant. I think it's an issue with the where the narrow trailing edge of the keel joins the hull so will also rake this out and take a look.

 

[vyv_cox]

Pressure is going to be far more effective than vacuum, especially on viscous stuff like Sikaflex. It appears from your photo that this is a bolt rather than a stud and nut. Why not withdraw the bolt, squirt Sika into the hole and replace the bolt?

 

[Graham376]

That looks very messy, did you you use donuts of caulking cotton before bedding the plates?

https://wiki.westerly-owners.co.uk/images/8/88/Keel_Bolts.pdf

 

[ducked]

Id bet sikaflex cant be effectively vacuum infused. I think it'll be too viscous.

Opposite extreme: cyanoacrylate. Might not even need a vacuum, but you'd have to get the surfaces fairly dry first

If acetone is damaging as a cleaner/dryer (unconvinced but OTOH I'm not certain its ok either) then ethanol would be gentler, though it will take longer to dry.

As I said, I think there is a school of thought that holds that there shouldn't be any "flex" at all, and therefore flexible sealant isn't appropriate, but evidently you like, and already have it, so are stuck with it.

Just not very firmly.

I dunno really, but I could see that a keel that is allowed/encouraged to waggle around might start to overdo it.

 

[johnphilip]

It may be the result of the hull flexing. Once when the boat was lifted in the slings I was horrified to see a gap between the thin aft end of the keel and the hull. This is a particularly narrow / thin keel with several inches aft of the rearmost keel bolt. There was no leak internally but I was concerned. I did have the mastic fillet around the outside of the keel renewed when the boat was next lifted. It is important that the mastic is wide enough to accomodate any flexing an 10mm joint should easily take a 3mm movement but a 5mm joint has to stretch to nearly twice its size to remain intact.
I think the original issue may have arisen when the hull was blasted to remove flaking old antifouling and the mastic fillet was renewed with the boat in its cradle when the hull weight would have closed any gap there was.

 

[vyv_cox]

A gap between keel and hull has always become evident with our boat in the slings. Bolting at the aft end of the keel is minimal due to its narrowness in this area, nearest bolt maybe 12 inches forward. The hull flexes a little but the bolting is secure. In 30 years not a drop of water has entered through any keel bolts.