Plywood boat leaks :(

[kevinb]

Hi all

I'm a first-time boat-builder although I have (or so I thought) reasonable carpentry skills. I've built a small plywood flat-bottom scow-type boat, with hard chines. The plywood panels are glued-and-screwed onto the chines, but I've not used any other method of waterproofing so far. It's only a toy boat and I wasn't expecting it to last more than a year or so.

My first test on the water was not a great success. On the one hand, I was pleased to find that the structure itself was pretty rigid, and it was stable in the water. On the other hand, it leaked. A lot. After ten minutes in the water there was probably a couple of pints on board.

I have a total budget for the construction of zero. So far, I've used stuff I had lying around in the workshop. What I don't have lying around is fibreglass tape, marine epoxy, or any of that high-tech stuff. I could probably fix the leaks by sealing the joints with expoxy and fibreglass (or polyester and fibreglass, at a pinch. But either would bust my budget.

I do have access to a load of army surplus two-part epoxy paint, and I'm wonder whether a number of coats of that would be sufficient to seal up the small leaks. On the other hand, the leaks might be too big to bridge the gaps with paint. Or could I get away with caulking the insides of the joins, with marine sealant or something? It hasn't got to last -- low cost is the main factor.

I'd be grateful for any kind of advice anybody can offer.

Best wishes
Kevin

[Kay9]

Duct tape and your 2 part epoxy should give you a leak free eniroment for the 6 months to 1 year life you expect of your boat.

K9

[PAR]

Duct tape and epoxy paint isn't going to work.

You have a few options. The best is to seal the moisture out of the joints from the outside. This requires the joint be covered with a gap bridging glue and probably some sort of reinforcement, like 'glass tape.

You can try plain old tub and tile caulk. Mash it good into the gaps and seams. Before it cures, rip up one of your mother's fine bed sheets into 2" (or wider) strips. Stick these strips on the caulk, over lapping the seams. Lightly spray with water, to dampen the fabric. The caulk will start to run a little, but at the same time it'll soak into the good sheets you mother's going to kill you over when she finds out. Now smear on some more caulk, trying to cover the linen strips completely. Paint it up in a Zebra pattern, which should hide the lumps and bumps on the fancy caulked up seams.

This will give you a season of light use, but it's easy enough to remove with a grinder when you can afford some real stick-um in a can and 'glass fabric.

Epoxy paint will fill very small gaps, 1/64" or smaller, like sanding scratches, but little else. You might be able to get the table cloth linen (again don't let your mother know you've stolen it) to wet out with the epoxy paint. This might work for a while. Lots of paint, once you've got it stuck to the boat, in hopes it will seal the pores and lock it down tight.

[kevinb]

Thanks for the suggestions. I think part of the problem is that there aren't any (visible) gaps or cracks between the plywood bits, or between the plywood and the chines. As per the instructions in the August 1952 edition of `Practical Woodworker', I planed the chines completely smooth before screwing down the plywood. I put screws every six inches. What gaps there are must be absolutely microscopic Obviously not microscopic enough to stop water seeping through. But there's just not enough of a gap to push caulk into. I could, perhaps, grind the joints open a bit so I could stuff some sealant in, but that seems a bit back-to-front.

Fibreglass tape is cheap, but epoxy isn't. I can perhaps afford a little, if there's no other way, or if it's really superior to any of the alternatives. If I were to put a coating of epoxy along the outside seams, then bed in some glassfibre tape, then enough epoxy on top to fill the weave, is that likely to be sufficient? Could I thicken the epoxy to make it fill better? I'm kind of worried that the epoxy/fibreglass composite would crack with movement of the structure and leave me no better off.

As I said, it hasn't got to last. I've already got an idea about making a two-part nesting boat that will suit the family purposes better. So I'm happy to treat this first one as a throwaway prototype. But it's not very agreeable paddling around in a boat that's two inches deep in the bilges in freezing cold water in January.

[PAR]

Water can mitigate through just about anything. Joints that look tight can leak with water pressure trying to force it through the seam.

It's very likely you design was intended to be kept "wet" during the season, then permitted to dry out in the off season. Before putting anything on the seams, place the boat in shallow water and leave it there for a few days. The water only needs be just as deep as the hull draws at rest (a few inches). This will probably swell the wood tight along the seams in a day or two.

If the boat is kept in this swelled up state, then it will remain tight, but if allowed to dry out, it'll leak again and you'll have to "soak" it again.

I'm not sure what design you've built to, but having to swell up a small boat is a pain in the butt, unless you have lake or river front property.

The only way around this is to seal the seams with goo and fabric.

No, the epoxy will not break, if applied properly over cloth. It truly is far better then anything else. You'll need less then a quart for a small boat's chines.

[kevinb]

Thank you for your advice. I'm not working to any particular design, but the thing I've built is very much like the designs that were published for flat-bottom utility and fishing boats in the 1950's. Well, I suppose if you've got plywood and lumber and access to woodworking tools, making a frame and screwing plywood onto it seems a common-sense approach.

But I wonder if any of these boats were ever truly watertight, unless they were kept wet? As you say, water doesn't need much of a gap to creep through, especially under pressure.

Sigh. I'm more-or-less resigned to sealing the chines at least with fibre and epoxy. The problem is that a quart of marine epoxy costs about £100 in the UK. I don't know how expensive it is in the rest of the world. That's £100 more than I intended to spend, and certainly enough to buy me a second-hand GRP boat.

[masalai]

Welcome to the world of boats... definition: a boat is a hole in the water into which one pours money to keep the water out.... Whilst one is planning and building one is in total denial of this fact, and thereafter the retort is "well it is a boat!" etc....

[ned L]

Let me start by saying I'm a traditionalist cedar & copper rivet kind of person person, but understand the practical approach you need. Are you able to back out the screw holding the bottom on & separate the bottom from the chine? If so, I'd apply a bead of paneling adhesive in the seam (regular residential construction grade stuff, about $1.50 US a tube here in the states, one tube should do it) and tighten the screws back down so that a small bead squeezes out of the seam. You wrote that you only need a year or two, this will far outlast that.

[kevinb]

Originally Posted by ned L

Let me start by saying I'm a traditionalist cedar & copper rivet kind of person person, but understand the practical approach you need. Are you able to back out the screw holding the bottom on & separate the bottom from the chine? If so, I'd apply a bead of paneling adhesive in the seam (regular residential construction grade stuff, about $1.50 US a tube here in the states, one tube should do it) and tighten the screws back down so that a small bead squeezes out of the seam. You wrote that you only need a year or two, this will far outlast that.

Sigh. I wish I could. But I sealed the screw holes with epoxy putty (because I had some left over from a car repair) :/ Oh, well, we live and learn.

I'm not sure how good a guide the prices on eBay are, but I notice that marine epoxy resin costs approximately four times as much in the UK as in the US. Don't know why.

I have invested in the smallest available tub of epoxy (200 ml) -- and even that was expensive -- and mixed it up with a bit of thickener and crammed it hard into all the seems and edges both on the inside and outside. I was just able to do the whole thing with that amount. I'll try it on the water when it's cured. If that fails, I guess I'll have to bite the bullent and buy either a sensible quantity of epoxy and glass tape, or a second-hand boat, whichever works out cheapest

Or I could just start again and put this one down to experience. Wood I've got. It's everything but wood that I haven't :/ And I really want to build a nesting boat, now I've realized that such things are possible...

Originally Posted by kevinb

Sigh.

I have invested in the smallest available tub of epoxy (200 ml) -- and even that was expensive -- and mixed it up with a bit of thickener and crammed it hard into all the seems and edges both on the inside and outside. I was just able to do the whole thing with that amount. I'll try it on the water when it's cured. If that fails, I guess I'll have to bite the bullent and buy either a sensible quantity of epoxy and glass tape, or a second-hand boat, whichever works out cheapest d...

A bit late unfortunately but maybe not too late. 21 quid per 1,5 kilogram thats much resin for your task.
here:
http://www.epoxy-resins.co.uk/Shop/resin.html

Could I thicken the epoxy .............. ?

No no no...........
You did already to fill gaps ok. But if you have to saturate the wood and apply the glass, the resin should be of low viscosity to soak into the material!
Please browse this forum for more advice there are lots of better advisors than I am.

wish you succed !

Regards
Richard

[PAR]

Since you've got thing fairly well dogged down, all you can do is butter up the seams with a sealant, like 3M 5200 and hope it seals the leaks.

Construction grade adhesives don't work. They're brittle, usually not water proof on wet wood and lack the elongation necessary to work as a seam sealant. It's fine for holding up paneling in your family room, but nearly worthless on a boat, particularly submerged, it even says so on the side of the tube.

With a little luck, your down and dirty epoxy job will hold for a few years, which is all you needed anyway.

[kevinb]

Originally Posted by apex1

A bit late unfortunately but maybe not too late. 21 quid per 1,5 kilogram thats much resin for your task.
here:
http://www.epoxy-resins.co.uk/Shop/resin.html

Cool. That's the cheapest I have seen epoxy in the UK. It's almost affordable Thanks. I will bear this in mind if my dirty repair doesn't do the trick.

Originally Posted by kevinb

Cool. That's the cheapest I have seen epoxy in the UK. It's almost affordable Thanks. I will bear this in mind if my dirty repair doesn't do the trick.

Always a pleasure....... you´re welcome
and have a look here:
http://www.westsystem.com/ss/applying-cloth-tape/
before you mix the whole pot of resin!
sometimes the bloody Germans have some value



Regards
Richard

[kevinb]

Well I'm pleased to report that, since sealing the joins with thickened epoxy, my cheapo boat is now _almost_ watertight. There's still a tiny seepage under one of the chines, which I suspect I can seal up with epoxy putty. Then, hopefully, with a couple of coats of battleship paint it should be good to go.

As it happens, this may be academic, because a chap up the road is selling his old Mirror for £150, which is probably less that I need to spend to finish my home-made boat. Oh well. It's been a learning experience, anyway. Thanks to all who replied.

[furasta]

Don't be so quick to abandon your project. My father-in-law just sold his old plywood flat bottomed dinghy for $20. He made it from construction grade plywood nearly 25 years ago. My wife had mistakedly, back then, named it 'Fat Chance' :-)