Correct way to fix fittings through the deck

Nostrodamus

Nostrodamus

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I have just had an "A" frame made for our boat which will support solar panels and a dinghy.
Each of the 4 feet has a round stainless steel flange with holes for 3 bolts to go through the teak and fibreglass deck.
I will put a backing plate underneath the hull to fix the bolts through and disperse some of the load.
To make the holes waterproof I need to put sikoflex or something similar under the legs.
Obviously if I just put some sikoflex there and put the legs on top the weight will squeeze most of it out.
Is there a correct way to fix something like this to the hull.
Thanks for any advice.
 
What I do is to seal the sides of the holes I have drilled with epoxy resin. The reason being that if/when the sealant deteriorates, the water won't penetrate into the laminate or timber.

I bed the fitting on a layer of CT1 with a nylon washer between the fitting and the deck to prevent all the sealant being squeezed out when the nuts are tightened.
 
Parsifal makes a good point.It is very important to seal the "sides" of the holes,where they pass thru the cored GRP deck.
Drill holes thru teak & GRP a bit oversize. Use a bent finish nail in drill to route out some of the core. Put a piece of tape over the underside of each hole. Fill hole to top of GRP deck with epoxy resin. Re-drill holes to proper size. Chamfer top of holes a bit-this will allow sealant to form an "o-ring" around bolt.
Cheers / Len
 
parsifal said:
What I do is to seal the sides of the holes I have drilled with epoxy resin. The reason being that if/when the sealant deteriorates, the water won't penetrate into the laminate or timber.

I bed the fitting on a layer of CT1 with a nylon washer between the fitting and the deck to prevent all the sealant being squeezed out when the nuts are tightened.
Click to expand...

I really like the idea of a Nylon washer between the fitting and deck. Sound very sensible as does the epoxy. Do you leave the sikoflex to cure a little before finally tightening the fixing? (What's CT1)
 
Nostrodamus said:
I have just had an "A" frame made for our boat which will support solar panels and a dinghy.
Each of the 4 feet has a round stainless steel flange with holes for 3 bolts to go through the teak and fibreglass deck.
I will put a backing plate underneath the hull to fix the bolts through and disperse some of the load.
To make the holes waterproof I need to put sikoflex or something similar under the legs.
Obviously if I just put some sikoflex there and put the legs on top the weight will squeeze most of it out.
Is there a correct way to fix something like this to the hull.
Thanks for any advice.
Click to expand...

IMO Butyl tape is one of the best ways to seal fittings, it never hardens and will last the life of the boat. If you ever need to remove it again it should be easy to do so. If your deck is cored, its important that you drill the holes oversize, fill with epoxy and redrill through the epoxy. Water in the deck could cost a lot down the line.
If the backing plate is aluminium or stainless then you can tap it for the bolts. (Use duralac when you install them), if its a wooden backing plate, make sure to use big washers to spread the load.

Theres an excellent guide on bedding marine hardware here:
http://www.pbase.com/mainecruising/rebedding_hardware
 
The main problems of mounting a structure like that on a teak deck can be put into 2 distinct points.
1 Teak deck seams and camber.
The seams that run under the Stainless Plates can be a trough for water to run in, and holes for mounting may pass through them. The plates may not also fit the camber of the deck exactly,
The best way to sort both these issues out is to cut a circular teak pad perhaps 10 to 12 mm bigger than the Stainless mounting plate, and 12 mm thick. Shaped to fit between the deck and the plate [ screwing temporarily in place and using pencil lead rubbed on the plate to pick up the high spots sorts that out ] Putting a nice radius on the edge is a nice touch too. You can then use an oil based teak mastic under the pad, and sikaflex under the Stainless pad giving you an almost perfect seal.
2 Leaks trough the bolts.
Whatever bolts you are using I always suggest the use of boat cotton on the bolts, wrapped around with mastic, and never bother with the washers and mastic underneath.[its messy and if the water is getting that far you have a problem anyway.] Its an old method but still works well in my book, and if the teak pad has been made well enough it will be fine. Stiffening plates should just need a thin bead of sikaflex on them.

If you look at winches and fittings on teak decks of yachts they use the pads to sometimes put angles on them to make the ropes run true, and prevent riding turns etc. It is a really professional look if you take the time to get it right.
Good luck
 
Len Ingalls said:
Parsifal makes a good point.It is very important to seal the "sides" of the holes,where they pass thru the cored GRP deck.
Drill holes thru teak & GRP a bit oversize. Use a bent finish nail in drill to route out some of the core. Put a piece of tape over the underside of each hole. Fill hole to top of GRP deck with epoxy resin. Re-drill holes to proper size. Chamfer top of holes a bit-this will allow sealant to form an "o-ring" around bolt.
Cheers / Len
Click to expand...

Absolutely correct - if the decks are cored, as most are in most areas. The OP does not say, just that they are teak covered. If the decks are cored and you bolt down without replacing at least some of the soft core with a harder material you will just have a crushed core and probably damage to one or both GRP layers, plus probable water leakage into the core, which is bad news.

As the OP is taking about a pretty substantial structure (support a dinghy as well as solar panels), some reinforcing of the underside of the deck might be more appropriate rather than just bolting down. If a non-cored GRP deck just some extra layers of GRP to spread the load then backing pads, but if cored cut away the entire inner skin and core and put on several new and larger layers of GRP tieing the inner and outer cores together with just solid GRP where the holes are to be.
 
I have posted this a couple of times before, taken from 'Glassfibre Boat Manual' by Bo Streiffert. How to mount fittings on a cored deck.
Deckfittings.jpg


Otherwise, don't stint on the sealant. I am currently overcoming water ingress problems caused by the habit of a previous owner of using the least sealant he could get away with to bed deck fittings. I find that if enough is used, a generous covering, plenty of excess extrudes into the bolt holes, sealing them perfectly. With a flanged fitting the practice most often advocated is to not tighten the bolts fully until the sealant has gone off. However, if using this method it is essential that the bolts are not turned, as this will tear the sealant and allow a passage for water. So I usually don't bother, just tighten up fully while the sealant is still wet.
 
I don't get this 'use plenty of sealant' argument. If all the holes through the deck are filled, what is the sealant under the fitting doing? Likewise applying sealant on the underside of the deck is a waste - if water has penetrated the top of the joint, you are just containing it and forcing it to saturate the GRP fibres. I do form a 'countersink' on the outside of boltholes to make a better seal around the bolt.
 
ghostlymoron said:
I don't get this 'use plenty of sealant' argument.
Click to expand...

You would if you had my boat :eek: The beloved previous owner believed that a tiny blob of silicone (ugh) somewhere near the bolt was sufficient. We have spent months trying to get the deck watertight because of this. I don't advocate using massive volumes but I always circle each bolt and the perimeter of the fitting with Sikaflex/PU40.
 
Its also worth saying DON'T USE SILICON.
Hate the stuff, impossible to ever remove properly.

The only time I'd ever pick Sikaflex over Butyl is in below water fittings.
 
Double checking my technique

from 'Glassfibre Boat Manual' by Bo Streiffert. How to mount fittings on a cored deck.

image: http://i77.photobucket.com/albums/j62/vyvcox/Yacht tech/Deckfittings.jpg

I have been using my hole saw today following exactly the process above. Before I get to the epoxy stage I have another series of bolt holes that need drilling out and epoxy-ing, however the fittings on deck are two strips of wood that I do not want to disturb. I am guessing that infact this makes little difference. I remove the old bolt and drill down through the wood strip with an oversize hole, go underneath and drill out the lower skin plus balsa core, and then fill everything, including the wooden strips with epoxy. Then drill the epoxy for the appropriate bolts size and fit new bolts with sikaflex (or butyl tape) as suggested. Does this sound like the right technique?

The wood strips are those that hold the sliding hatch in position so they are quite substantial bits of timber, they hold the guide rails.
And secondary questions....
1. Having not used epoxy before I will use thickened epoxy from underneath, I presume if I get the consistency right it will hold itself in and not plop out... (peanut butter mix)?
2. However to fill the enlarged drill hole in the top timber I am guessing a runnier mix (even neat?, no thickener)

Many thanks for any guidance. :)
 
Fairweather Dave.
About the way I was told and it will save getting it all over.
Tape the hole with a strip underneath so it is flat and pour or squirt the expoxy in the hole from the top if it is big enough.
Putting it in from the bottom as you suggest will be a nightmare and you may end up stuck below decks for some time in a huge mess. You can leave the tape on until the exopy is cured.
 
Thanks Nostrodamus, yes you have highlighted exactly what I was wondering about. But what tape to use if I go that way?? I tried some duck tape for holding a batten but it was worse than useless. There was no visible sign of dampness on the grp but the duck tape did not stay up longer than a minute before it started to droop like wallpaper put up by Frank Crawford......
 
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