hull/deck joint

[Ardenfour]

my hull and deck joint leaks. The deck moulding is flat round the edges and rests upon the hull which has a lip/flange towards the inside. the overlap is about three inches and has at present a foam rubber gasket between the 2 faces. The whole thing is through-bolted every 4 inches through the alloy toerail. The entire rail is removed on one side and the foam is wet. When I step on the deck edge the water squirts out. I can prise the deck and hull apart with screwdriver so no adhesive. I will shortly be covering the boat with tarps to dry out.
Should I remove this gasket and introduce sealant or rely on the bolts to tighten it back down and reseal it? Also I'm considering glassing over the joint on the inside with epoxy and woven tape - how many layers might I need to apply?

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[William_H]

O dear you have a problem it seems to me. Now for lack of other responses my boat is similar design but is stuck together with a bog ie resin with filler that has squirted outon the inside and is pop rivetted to hold it together presumably while the bog hardened. 25 years later no problem. I woukld suggesst rather than epoxy tape on the inside you prise apart the join as far as possible and inject a filler into it. Either a mastic or an epoxy with filler or even araldite which is naturally thick. (make it warm)
What does everyone else think? good luck will

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[oldsaltoz]

G'day Peter,

Glassing the inside is an all but impossible task and you risk trapping water in bulkheads as glassing behind them is not viable though not impossible, access around the bow and stern can be a almost impossible also so you may end up still leaking after several days work.

As the deck is not something anyone plans to remove later, unless someone did a bad seal job in the first place and looks like that what you may have.

I think I would remove the foam rubber and fill the gap with an epoxy resin mixed with Micro-fibres, this makes an extremely strong joint.

You would have to remove the other rail and lift the deck so you can properly clean the join and lay up the resin, it has a pot life around 45 minutes, just remove what squeezes out when still wet, it's very hard sanding when cured. Install every second rail bolt wrapped in cling wrap to keep the thread clean, then install the rest, again wrapped.

This stage is best done with some helpers, what are crew for anyway.

Just one last thing, check with the manufacturer fist to ensure this will not make her too stiff.

Or you could use lots of Sikaflex.

Andavagoodweekend........



<hr width=100% size=1> Old Salt Oz /forums/images/icons/cool.gif Growing old is unavoidable. However, growing up is still optional.

 

[boatmike]

A common problem with this type of structure I am afraid. I partly dissagree with the other post in that I think taping around the inside of the hull/deck joint with about 4 layers of 4"-6" tape is in fact the best solution but he is right that you need to relieve the bulkheads in way of the joint far enough to make the joint continuous and then re-instate the boundary angle joint to the bulkheads afterwards or you will only ensure the water gets into the end grain of the bulkhead. This is a big job and only to be tackled if you feel confident that you can do it properly which means grinding or sanding the area very thouroughly before adding a CSM layer topped off with about 3 layers of light woven rovings... You will also find polyester resin much easier to work with than epoxy and as it is what the boat is made out of anyway there is no reason to use anything else. When this has been done, remove the rubber gasket completely and fill the gap with Sikaflex. Then replace the bolts sealing these with Sikaflex too. Guarantee it won't leak afterwards! This is a lot of work though and you could try the sikaflex treatment first without the taping which would be a lot easier. What you need to remember though is that you are still relying on the bolts for strength and some flexing will still take place. The "GRP solution will actually make the joint much stronger if done properly.
Either way good luck!

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[snowleopard]

with an existing rubber gasket there is bound to be some flexing so any solution involving sticking permanently has to be strong enough not to break as the boat tried to flex. injecting epoxy into the joint will not provide this strength unless you could open up the joint and thoroughly abrade and degrease the mating surfaces, also they would need to be a pretty close fit. (the manufacturers would probably have done that if it were feasible).

to tape over the join from the inside needs a minimum of 4" each side of the join, one layer of chopped strand mat and 2 or 3 layers of bi-axial fabric with the fibres running at 45 degrees. very thorough abrasion is required before applying. polyester resin (isophthalic) is fine, it sticks just as well as epoxy. getting at the seam all the way along will be hard work and the mess from sanding will be a nightmare.

in your shoes i would lever open the joint, get it clean and dry and squirt in lots of sikaflex. don't bolt down tight until the gunge has set.

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[kds]

Great to hear from you again - keep smiling !
I was suprised to see the suggestions to use polyester on an old hull. It is an area which I wondered about on mine. Don't forget that you can also pull the toe-rail down sikaflex and onto the joint, which will help. Being realistic - follow Snowleapard's suggestions.
Ken

<hr width=100% size=1><A target="_blank" HREF=http://www.canongrange.co.uk>Bed and Breakfast, cathedral Green Wells, Somerset Canon Grange</A>

 

[Ardenfour]

Thanks for all replies. I've got to the stage now with the boat that I have access to the underside of the full length of the deck joint on both sides. Two of the bulkheads need repairing where water leaks at the chainplates have caused rot - I plan to graft new sections in, so access to the joint above these is no problem. Also got the whole boat under tarpaulin today for the drying out process to commence. I thought a combination of wedges and wooden props to raise and seperate the joint along it's full length would allow removal of gasket and drying out. As this will probably take several weeks in this weather, is the grp likely to be deformed permanently, or will it spring back to it's original shape?
How quickly does sikaflex cure? The foam gasket when compressed is around 1mm thick. If it sets quickly I could end up with problems getting the sikaflex to squash down to that thickness, bearing in mind I'd have about 110 nuts and bolts to fit to clamp the assembly down tight.
I also thought (from any books and other research) that polyester resin has poor adhesive qualities on cured grp layup, and that epoxy was the only thing to use for repairs and additions to polyester grp - any further comments, anyone?

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[snowleopard]

answering a few of your questions- grp will spring back unless you force it so much it cracks.

sikaflex needs 2 or 3 days to set. the joint should be closed and bolted down but not tight, aim to leave about 1mm thickness. when bolting down tight, hold the bolt and turn the nut so as to avoid breaking the seal around the shank of the bolt.

as for those who say you can't stick new grp to old, don't worry about it. this technology has been thoroughly tested and boats that, like mine, are built entirely of grp panels bonded together with tape are showing no signs of failure after 30 years hard use. the requirement for a good bond is to abrade thoroughly, preferably using coarse sanding discs in an angle grinder.

if you decide to renew the foam in the joint, try <A target="_blank" HREF=http://www.sealsplusdirect.co.uk/>these people</A>

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[Boathook]

Re: hull/deck joint re halcyon23

I remade our hull/deck joint last winter. First I removed all the old sealant where possible. I then tightened up all the machine screws I could and filled any gaps left with sikaflex. The overlap joint then had sikaflex on it plus I then covered all all the screws with sikaflex. The joint on the inside was mainly glassed up and the majority of the water came in through the lose screws. So far it remains all dry inside.

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[PaulS]

My reading on the subject leads me to the same conclusion.
Epoxy supposedly has much higher bonding strength and adheres much better to a wider mixture of substrates than polyester.

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[snowleopard]

yes, always remember that epoxy is an adhesive while polyester is just a plastic. for example you should never use polyester to bond plywood as the join will fail in time.

bonding to cured polyester is a special case. derek kelsall who has been designing GRP boats for over 30 years has done a lot of research on construction methods and his conclusion is that a post-cure bond using polyester has around 80% of the strength of a one-piece moulding. the same bond using epoxy gives around 70%. all his designs are constructed from GRP panels joined with tape.

i did my own experiments on surface preparation and found that it is essential to abrade thoroughly. applying polyester to untreated GRP had virtually no bond strength, when abraded, failure generally happened within the laminate, not along the joint line. de-greasing made no difference.

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