SailNet Community banner
  • SailNet is a forum community dedicated to Sailing enthusiasts. Come join the discussion about sailing, modifications, classifieds, troubleshooting, repairs, reviews, maintenance, and more!

How to put epoxy for screw mounting into a void???

6K views 37 replies 14 participants last post by  jfdubu 
#1 ·
Hi All...

This is a hard problem to describe. My cockpit is not cored or anything like that, just a solid piece of plastic. Below it is a liner and there is a half inch to one inch gap between the two.

So, I want to mount something in the cockpit with screws. I can of course drill through but the hollow is not going to provide much stability. I can't fill it with thickened epoxy because it will just spread out and not build up.

I'm thinking I could drill a hole, and maybe insert some kind of thin tubing by crushing it down, sticking it into the void through the hole and then it might expand into something that could contain the epoxy.

Alternatively I could cut out the liner and just use fender washers directly under the cockpit but in some cases I don't have access under the liner.

Not a great idea but its all I got. Anyone have a better idea?

Thanks!
 
#2 ·
You can spray some polyurethane to the void and wait for it to cure. After it cures you can redrill and clean the polyurethane foam around the void by a bent nail attached to drill. This will give you a "room" to pour in epoxy. This way two layers will be fixed. You can redrill the layer - epoxy - layer again and use screws.
 
#5 ·
... and the make and model boat would be useful too. For instance, I am working on a Hunter 216, which is NOT made of FRP, but of Luran.
 
#6 ·
Sounds like you need to remove the headliner to get access. If there is no core, you don't need to inject epoxy. That's for sealing core. Depending on what you are mounting and thickness of the cockpit layup, you may or may not need a backing plate.
 
#10 ·
Wow, lots of great ideas THANKS!

By "spreading out" I meant just basically flowing in the giant void without actually building up.

To answer the questions, the boat is a Scampi 30 MK IV built in Newport, RI. I'm looking to remount the traveler, which currently is mounted with screws through the void and as a result moves around under load. I also want to mount some foot rests for when people are sitting up on the deck when heeling.

The void causes this stuff to not be mounted securely, and that's why I wanted to fill with something hard like epoxy. Also, I want to avoid leaking down into the quarter berth below the port side of the cockpit.

Soaking a piece of foam and stuffing it in there seems like a pretty cool idea...
 
#16 ·
Okay, now I understand what you are trying to do. I would use 3M 5200 quick set. If you are drilling new holes, drill only the top hole then fill in excess with 5200. You might need two applications to get it to fill to the top. Then when dry, drill your hole thru.

If you are dealing with existing holes, do the same, but duct tape the hole on the underside.

5200 can be had cheap at Lowes in small amounts or full caulking tubes ($15.00ish).

Now on something like the track that is a one time install I would also glue the track down with the 5200. Items can be removed that are mounted with 5200 by using a wire saw. If you just try to pry an item up held down with 5200, you will take the parts of the deck up with it. It is stronger than the decks. If you want to down grade that, use 4200.
 
#17 ·
Archer,

Go back to the foam suggestion. I wouldn't worry about water absorption, if water gets in the holes aren't sealed properly (see butyl tape). Now, where you can get to the underside, bolt and washer is the most secure and easiest to seal. Where you must use a screw inject the low expansion foam and wait. This stuff takes awhile to fully expand and cure. Then drill your hole and fill w/ epoxy. Make sure you know how long a screw you can use.

I've used this foam method on a below the waterline crack where I ground all the bad stuff away and injected the foam. Came back the next day to find giant wart (foam ball) had grown out of the hole. Cut it back to the shape of the hull and glassed it all back. came out strong, water tight and after a barrior coat looked like the original hull.
 
#18 ·
Archer,

Go back to the foam suggestion. I wouldn't worry about water absorption, if water gets in the holes aren't sealed properly (see butyl tape). Now, where you can get to the underside, bolt and washer is the most secure and easiest to seal. Where you must use a screw inject the low expansion foam and wait. This stuff takes awhile to fully expand and cure. Then drill your hole and fill w/ epoxy. Make sure you know how long a screw you can use.

I've used this foam method on a below the waterline crack where I ground all the bad stuff away and injected the foam. Came back the next day to find giant wart (foam ball) had grown out of the hole. Cut it back to the shape of the hull and glassed it all back. came out strong, water tight and after a barrior coat looked like the original hull.
This what I'm leaning toward doing. The stuff-the-foam-into-the-void idea seems like a good method but I need to use thickened epoxy for strength and I don't know if thickened epoxy would seep into the foam thoroughly. This method would create a void that is 100% filled with epoxy.

And everywhere I'm doing this, I'm planning to use through bolts with backing plates or at least washers underneath.

What foam do I use? Just the ordinary minimally expanding stuff from Home Depot?
 
#20 ·
Good ideas for getting the epoxy into the void, but I'm not sure it's the solution.
The thickened epoxy trick is to keep water migrating down the fastener hole from spreading into the wood core. Not your problem here. What it sounds like you're talking about is the equivalent of a backing plate.
I don't know whether a gob of thickened epoxy will serve for that, but I'm skeptical. Backing plates' effectiveness relies on their area as well as their strength. You have little control of either when you squirt goop into a void you can't see.
I'd bite the bullet and cut the liner. Install a proper plywood or metal backing plate at least the size of the hardware you're mounting. Your challenge then becomes cosmetic--covering the hole in the liner in an attractive way. But that's a lot easier and less critical then hoping a glob of epoxy you can't even see will help hold your mainsheet traveler in place.
John V.
 
#22 ·
Some random thoughts... If I cut the liner and just bolt to the underside of the thin deck, my thinking is that I'll have much less strength. By making the deck thicker, I can make the platform much stronger. But for that to be true the upper and lower skins need to be bonded together somehow. I was hoping that the epoxy plugs spaced apart would provide that bonding as well as providing mounting points for the bolts.

Right now, the area is hollow so it's true there is no core to protect with the epoxy. The main idea is to keep the void from crushing by providing support inside the void. Even in a cored deck, making an opening in the core and filling with epoxy protects the core but also provides much more cruse resistance. If I do this, the backing plate would be under the liner. Cutting the liner would work in some places but there are some places where I can't do that.

Still, if I can do it, cutting open the liner from underneath and using epoxy to adhere some balsa core should, in theory, greatly increase the strength of the area. I could then drill through that balsa, widen it with the drill/alan wrench method and fill it with thickened epoxy.
 
#23 · (Edited)
I think that a piece of hardware that takes a load needs to be mounted on a surface that spreads the load out well past the size of the base. Maybe you can cut out just enough from the underside to slip in/epoxy a good solid filler that will provide a firm mounting area. You can put the cut out piece back in at the same time, tape off underneath. A backing plate underneath when you install the equipment will hide, strengthen, and overlap your cut perimeter. The undersides are usually relatively thin, so some flex may make getting the solid piece in pretty easy. Think I'd slide in layers of wood or whatever, glued into a laminate. That'll make it easier to get the piece in and minimize the cutout.

I think using some layers of good-and-dry CCA treated YP lumber, sliced 1/8" or so thick might work well and provide rot resistance. The YP bends well. They'd be easy to epoxy up and slide into a slot. Balsa core would require a larger cutout to get it in. I think if you're tricky you can do it and never see any damage.
 
#25 ·
Still, if I can do it, cutting open the liner from underneath and using epoxy to adhere some balsa core should, in theory, greatly increase the strength of the area. I could then drill through that balsa, widen it with the drill/alan wrench method and fill it with thickened epoxy.
Jarcher, a couple observations re your post. First, you can't be sure the epoxy will adhere to either deck or liner without cleaning and roughing each surface.
Crush-proofing the space between the liner and deck is important, and epoxy might work with the right choice of thickener, but you need more than that. Your deck will flex with strain on the traveler. A backing plate reduces flexing at the fasteners, basically spreading the strain around and reducing the likelihood that the fiberglass will eventually crack near the screw holes. If your epoxy 'glob' breaks or isn't big enough, it won't help in this regard.
Finally, coring with balsa stiffens the deck but won't serve as a backing plate. I'd use exterior grade plywood, a 1/4" thick piece of aluminum or something similar. Incorporating the liner into that structural sandwich may or may not do anything for you. Liners and hulls/decks normally should flex independently of each other.
John V.
 
#28 · (Edited)
Hm... Okay thanks for the tips everyone. I see I need to give this much more thought. The traveler has been mounted where it is for years, it came this way, and I have always felt it was wrong. In heavy wind the deck will flex a bit when trimming hard. I was planning a backing plate to spread the load under the liner, but if that won't do it then I guess I need to cut into the liner, install something as you all suggested, then repair the cut liner. This is going to be a bigger project than I had thought or hoped, but hey, nothing is really easy.

I'll do some more measuring tonight and see what I have access to and what I don't.

Thanks again! I'll post an update after my measuring.

Jim
 
#30 ·
Jarcher,

yes the HP low expanding foam will work. Anything more may distort the headliner. This foam forms a pretty tenacious bond with what ever it touches. You go back to the allen key hole hone to make a bigger hole to form your epoxy bridge.

Now if your deck was flexing with the old mounting, presumably screws, this will be a little stronger but not as strong as the backing plate/fender washer method for the traveler. As a foot rest, no problem in shear.

John
 
#31 · (Edited)
This weekend if I can find the time, I'll see if I can grab two small sheets of plexiglass or something, build them together with a 1 or so inch gap, and test this whole theory. I think this would be the best foam to try:

GREAT STUFF 16 oz. Gaps and Cracks Insulating Foam Sealant-162848 - The Home Depot

So I'll drill two holes (top and bottom) in the fake deck, insert the foam and let it cure. Then drill through it, alan wrench it out, fill with thickened epoxy and see what happens. Hopefully it will work, but if instead the chemistry creates a reaction that swallows up several city blocks, well, then we'll know. Or at least I will know, for the brief few moments before my death, and you'll all know since I won't have time to post as I prepare to hear St. Peter pronounce my new residence...

If the experiment is a success, I'll start with the foot rests and see how that goes.
 
#32 ·
I used Great Stuff years ago to fill the gaps between the roof and the reinforcement beams on a van. It stopped the kettle drum drone and made the the van MUCH more comfortable on the ears. I would venture to say you may not even need the epoxy as long as there will be no forces exerted on the screws, it will crush if the screws are over-tightened. You would still want to bevel the upper skin and use butyl tape under the washer. If it's going to bear a load the drill and fill with epoxy.
Btw, the foam also made the roof stronger and was still intact 200k miles later.
 
#33 ·
I'll see if I can grab two small sheets of plexiglass or something, build them together with a 1 or so inch gap, and test this whole theory.
It will probably have to be a lengthy experiment. Damage/weakness around the fasteners in your track probably occurred over a prolonged period of repeated stress.
You might try shooting an email to the epoxy manufacturer to get their input re the proposed application. The experiment you're planning may have been done already. They may suggest layering pieces of FG cloth rather than just using the filler alone.
Sorry to sound like a broken record, and I'll shut up after this, but backing plates are old-tech, and you're contemplating jerry-rigging a better mousetrap. I'd swap a structural problem for a cosmetic one any day, but that's just me. Remember though, if the epoxy-glob eventually fails, you'll have to cut a bigger hole in the liner so you can grind the stuff out again. I'd bite the bullet, cut the liner and do it right. You can worry about how to repair the resulting cosmetic problem as you sail your much-stronger boat.
JV
 
#34 ·
Actually I called WEST the other day and they had exactly nothing to suggest. I asked about the foam idea and they said "that might work." And that really was the sum total of their contribution. I doubt the guy could have been less interested in helping me if he tried actually.
 
#35 ·
As to cutting the liner, I'm really on the fence about it. If I cut it I really have to seal it back up because water would just pour out of it, as it had in the past when it was full of holes I sealed. If I put a backing plate in there then seal the holes I won't have access to the nuts. So, the nuts have to come all the way through the void, below the liner.

Any backing plate inside the liner would need to be accessible, and any backing plate under the liner does not solve the crushing problem. That's why I'm leaning toward using the foam and epoxy method, to at least solve the crushing problem. Installing G10 in there is more complex than it sounds because there is no way the void is a consistent size.

I'll get some pics...
 
#36 ·
Just to be clear, what I have been suggesting is installing backing plates in the void to stiffen the cockpit and/or bridgedeck. The nuts would be on the inside in the void above the liner. Then you would just need cosmetic covers of some kind to fill the access holes.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top