How to seal bolts below the water line

[Dazzajohm]

Ive just been working through the items highlighted in the surveyors report and as such have replaced the bolts for the bathing platform brackets which were corroded and requiring attention due to their proximity to the waterline.

When installing the new ones, the process I followed was to squirt some sikaflex in the hole, rub some around the thread and bold head, and paste some in the inside of the transom before securing the washer and nut in place on to it.

The bottom brackets are actually permanently underneath the waterline and it was clear from the drip marks on the inside of the transom and water in the bilge the previous ones had been leaking. I’m hoping I used enough sikaflex to stop any further leakage but I was wondering if there is anything else I can do / use before the boat goes back in to give it an even better chance of not leaking? Any kind of special spray or similar to provide a better seal?

Cheers
D

 

[black mercury]

I hope you replaced the bolts with stainless, if the old ones were corroded it may explain why they were leaking. No magic spray. If you used enough sealant for it to squelch out around the bolt head and inside when you tightened it up it should be ok. Have faith.

 

[VicS]

Ive just been working through the items highlighted in the surveyors report and as such have replaced the bolts for the bathing platform brackets which were corroded and requiring attention due to their proximity to the waterline.

When installing the new ones, the process I followed was to squirt some sikaflex in the hole, rub some around the thread and bold head, and paste some in the inside of the transom before securing the washer and nut in place on to it.

The bottom brackets are actually permanently underneath the waterline and it was clear from the drip marks on the inside of the transom and water in the bilge the previous ones had been leaking. I’m hoping I used enough sikaflex to stop any further leakage but I was wondering if there is anything else I can do / use before the boat goes back in to give it an even better chance of not leaking? Any kind of special spray or similar to provide a better seal?

Cheers
D

What happens here is that if any water can creep in between the bolt and the GRP crevice corrosion of the bolt will occur.

The secret is to make sure that there is sufficient sealant under the fitting , around the bolt and under the bolt head for there to be no little gap or crevice that water can creep into.
This applies to any stainless steel fastenings through the deck or hull.

If you see any tiny leaks, or even rust stains around a stainless fitting, it's time to remove and reseal. When the fastenings fail and something critical falls off it's too late. We were lucky not to lose the mast due to this! Wed ignored a small leak, because the water just dripped into the galley sink, for too long.

 

[Dazzajohm]

Thanks for the replies. Yep, replaced all 18 nuts, bolts and washers with stainless steel. Having not done this before I can only hope I used enough sealant - certainly was a bloody messy job although I didn't completely remove the bracket I just carried out the job replacing one bolt at a time

Is strange though as even now I’ve replaced these bolts and re painted with anti foul I am still getting a bead of water dripping from the outside of one from somewhere.

 

[ghostlymoron]

I drill a small chamfer on the exterior of the bolt holes with a countersink bit. Insert bolt and put a collar of sealant under bolt head (and under the fitting) and tighten. This forms a barrier at the wet end and excludes any water.

 

[VicS]

Thanks for the replies. Yep, replaced all 18 nuts, bolts and washers with stainless steel. Having not done this before I can only hope I used enough sealant - certainly was a bloody messy job although I didn't completely remove the bracket I just carried out the job replacing one bolt at a time

Is strange though as even now I’ve replaced these bolts and re painted with anti foul I am still getting a bead of water dripping from the outside of one from somewhere.

One not sealed properly then as a result of not removing the bracket and getting the sealant where it is required. Eventually crevice corrosion of that bolt will occur. What you dont know is how many other have gaps that the water is getting into as a result of short cutting the repair and will also suffer the same fate

No reason for the job to be particularly messy!

 

[RumPunch]

I redid my keel bolts afloat this winter. First two used Sikaflex 291, but wasn't convinced it had cured. Did the rest with The Dogs Bo**ox - which actually cures under water, then redid those two as well. Very impressive product, despite the suspect name

 

[Dazzajohm]

One not sealed properly then as a result of not removing the bracket and getting the sealant where it is required. Eventually crevice corrosion of that bolt will occur. What you dont know is how many other have gaps that the water is getting into as a result of short cutting the repair and will also suffer the same fate

No reason for the job to be particularly messy!

At the time, my thinking was it didn't make sense to unseat the bracket from it's position as that would be more likely to cause more problems than it would solve so just changed the bolts one at a time.

The boat isn't due back in until next week so I might consider re-doing at least the fixings of the bottom of the bracket which is permanently under the waterline.

 

[Dazzajohm]

I redid my keel bolts afloat this winter. First two used Sikaflex 291, but wasn't convinced it had cured. Did the rest with The Dogs Bo**ox - which actually cures under water, then redid those two as well. Very impressive product, despite the suspect name

Ok, that's interesting. Maybe I might be better to just leave what I've done and if there is a problem adopt your approach and repair with the boat in the water.

I used Sikaflex EBT... Not sure what the difference is between that and the 291 version.

 

[UK-WOOZY]

EBT isnt sufficient enough for below the waterlinein my opinion or if it gets submerged a lot. Ok for around the house or camper van or mounting solar panels. use 291 or 3M 5200.

were the bolts A4/316 steel?

 

[Dazzajohm]

EBT isnt sufficient enough for below the waterlinein my opinion or if it gets submerged a lot. Ok for around the house or camper van or mounting solar panels. use 291 or 3M 5200.

were the bolts A4/316 steel?

Hmm, OK. Maybe I should try do them again or just be prepared that I might have to re-do in the water part way through the year with something like CT1 Sealant.

I did do a search on here beforehand and although the question wasn't really answered people have asked before what the difference is between the two sealants and the consensus I got was not much if anything.

Yes, the bolts were A4

 

[VicS]

Ok, that's interesting. Maybe I might be better to just leave what I've done and if there is a problem adopt your approach and repair with the boat in the water.

I used Sikaflex EBT... Not sure what the difference is between that and the 291 version.

Hmm, OK. Maybe I should try do them again or just be prepared that I might have to re-do in the water part way through the year with something like CT1 Sealant.

Sikaflex EBT is a polyurethane adhesive sealnt similar to Sikaflex 291

Tech data sheet here https://www.sealantsandtoolsdirect.co.uk/pub/pdfs/Sikaflex_EBT_Technical_Datasheet.pdf

CTI is a silicone copolymer. Stixall from Toolstation is similar

PU40, from Toolstation, is another polyurethane adhesive sealant similar to Sikaflex 291

Stixall and PU40 are both "made" by Everbuild, who are a Sika company!

 

[rogerthebodger]

is another polyurethane adhesive sealant similar to Sikaflex 291

I was told by a sika rep that sikaflex 221 is the same as 291 without the marine price.

I am using 11FC in 600ml sausages and find that it keeps much longer than the 300ml tubes and cheaper too. The only snag is the gun for the sausages are much more expensive but better quality and last much longer.

Any comments Vic

 

[ghostlymoron]

11FC is fast cure which may come in handy if you're working between tides.

I was told by a sika rep that sikaflex 221 is the same as 291 without the marine price.

I am using 11FC in 600ml sausages and find that it keeps much longer than the 300ml tubes and cheaper too. The only snag is the gun for the sausages are much more expensive but better quality and last much longer.

Any comments Vic

 

[VicS]

I was told by a sika rep that sikaflex 221 is the same as 291 without the marine price.

I am using 11FC in 600ml sausages and find that it keeps much longer than the 300ml tubes and cheaper too. The only snag is the gun for the sausages are much more expensive but better quality and last much longer.

Any comments Vic

The tech data sheets for 221 and 29iI look identical ( somebody with time to waste will find some minor differences to prove me wrong I expect though)

Mechanical properties of 11FC don't look quite as good but no doubt more than adequate for a general purpose marine sealant

 

[ghostlymoron]

We used to use 11FC for sealing glass coated steel tanks containing sewage sludge. They never leaked!

The tech data sheets for 221 and 29iI look identical ( somebody with time to waste will find some minor differences to prove me wrong I expect though)

Mechanical properties of 11FC don't look quite as good but no doubt more than adequate for a general purpose marine sealant

 

[Malish]

Hmm, OK. Maybe I should try do them again or just be prepared that I might have to re-do in the water part way through the year with something like CT1 Sealant.

I did do a search on here beforehand and although the question wasn't really answered people have asked before what the difference is between the two sealants and the consensus I got was not much if anything.

Yes, the bolts were A4

+ I don't fully tighten down the nut until the sika has cured

 

[VicS]

+ I don't fully tighten down the nut until the sika has cured

If you tighten the nut after the sealant has cured be sure to counter-hold the bolt so that it does not turn.

If it turns you will have broken the bond between it and the hull and could have introduced a situation that will lead to crevice corrosion if not a leak.



Some will say tighten fully in the first place then do not disturb.

 

[ghostlymoron]

There was a long discussion on this recently. I think the concensus was tighten immediately then leave it alone.

+ I don't fully tighten down the nut until the sika has cured

 

[Dazzajohm]

Well I guess we will see as I tightened everything up straight away. Having put a splodge of sika on the inside of the transom for the washers and nut to tighten on to it didn’t make sense to let it cure before tightening.