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View Full Version : Uh-oh. Blister in plywood on dingy floor!



Jeff Kelety
07-18-2001, 06:42 PM
Back again. Sooner than I expected. As per Jamie, I have sweetly varnished, fir sole boards in my dinghy and she's back in the water. But this year after the first rain left an inch or so of water beneath, I found a blister in the plywood on the inside floor panel. This is the bottom of the boat, so obviously it's structurally critical. I can't remember if it was glassed all the way inside (probably not since this happened - it is al la, Bolger tack-and-tape method). The boat is glassed entirely on the outside.

So the question is, how to best deal with this. Dry her out, open up the blister, flush with epoxy and then glass over? I will get a cover in a bit to preclude this sort of thing, but it oughta be able to handle some standing water here. Any thoughts?

Thanks - again.

jgk

Bob Cleek
07-18-2001, 08:46 PM
Don't kill the messenger, but... ya gets what ya pays for. You elected to build cheaply and fast. You got a cheap boat that probably isn't going to last that long. Ordinary plywood isn't made to sit soaking in water. If you didn't even coat the inside of the ply with epoxy, it has no protection at all and is doing what any piece of regular plywood does when it gets soaked... it's warping and delaminating. Don't blame the boat. No, it shouldn't be able to oughta handle some standing water.

Dry out the boat completely. Then what you do is slice the blister right down the middle with the grain. Get a hypodermic syringe (sold where WEST System stuff is sold and elsewhere) and fill it with epoxy. Squirt it under the blister plenty with lots oozing out all over the place. Really get it in there. Then pile some lead pig on top of the blister to push it down flat while the epoxy cures. (Cover the repair with Saran wrap so you don't epoxy the lead pig to your boat at the same time.) That repair ought to last long enough. At least you will know that where you squirted the epoxy, the plywood is glued better than when it came from the factory.

dasboat
07-18-2001, 09:00 PM
Bob,where did you pick up the term "pig."That is a term used alot in the printing trade.Any connection?
Dasboat

Jeff Kelety
07-18-2001, 09:00 PM
<ya gets what ya pays for>

Ah com'on, Bob. Give it to me straight - don't sugar it <g>. Strictly speaking, I didn't build this creature. Twas my entry into wooden boats. The second entry, the Folkboat, is a bit more stout. But it's true, this little ply boat certainly wasn't made for staying in the water, but that's what I'm using it for. Ya get a whole lot more use if'n the boat's sittin' there ready for the kids to use.

So thanks for the fix. I'll patch her up. Get a cover and use her till she drops, then think of a suitable "real" replacement.

jgk

Phil Young
07-19-2001, 12:51 AM
Might be worth stripping back to bare wood and epoxy/glassing inside, at least in the area where water will stand.

Jeff Kelety
07-19-2001, 07:02 AM
<Might be worth stripping back to bare wood and epoxy/glassing inside, at least in the area where water will stand.>

That's just what I was thinking, Phil. Quicker than building a replacement. It got me to considering boats like the Shellback Dinghy and the more recent Ellen, though. These are glued up ply boats. No talk of glassing them, just paint and launch, I believe. The Shellback is tauted as a cruising tender, even. Is the difference in the quality of ply? My little dink, I know was built on a shoestring and didn't use marine ply. So can you just paint up good quality marine ply and let it stand in water after painting?

jgk

Greg H
07-19-2001, 08:52 AM
A lot of it is the type and quality of the plywood. Marine fir, unless it is glassed, will check and needs to be tended to constantly. However I have left untreated scraps of 6mil marine occume out in the weather for 3 years with no sign of delamination or blistering. I don't know how it stands up to sitting in the water for extended periods though. Greg

Bruce Hooke
07-19-2001, 11:07 AM
Non-marine douglas fir plywood goes to h**l in a hurry if it spends it's time anywere near water.

Marine grade douglas fir plywood does a bit better but still develops surface checks unless you cover it with fibreglass cloth & epoxy.

Occume and other top quality marine plywoods will last a VERY long time with just regular painting.

Glued lapstrake boats like Ellen should NOT be built with anything other than the best stuff (i.e., NO douglas fir plywood!).

Alan D. Hyde
07-19-2001, 01:15 PM
Chris-Craft Sea Skiffs were built for many years with marine fir plywood strakes. My boat was built in 1961. The strakes have yet to see either fiberglass or epoxy. They have been primed and painted with good quality marine paint.

The boat has seen plenty of water over the years.

A "checking problem" has yet to appear.

Alan

[This message has been edited by Alan D. Hyde (edited 07-19-2001).]

Keith Wilson
07-19-2001, 01:48 PM
Hey guys, this is an "instant boat", and should be fixed by instant methods. You shouldn't glass over a carvel-planked boat, likewise you shouldn't worry too much about a tack-and-tape one ;) Just grind out the blister, but not all the way through (any of the following: angle grinder, chisel followed by RO sander with 40-grit, nose of a belt sander, whatever's handy). Let it dry, then patch the divot with glass and epoxy. Sand flat to taste, but not too flat; it ain't a Herreshoff fer chrissake.

It probably started at an internal void, particularly if it was made with ACX fir. That kind of thing happens, don't sweat it. It almost certainly won't come back in the same place, although there maybe a few more lurking elsewhere. Generally not a problem if you catch it before it rots much.

Bruce is absolutely right - glued lapstrake requires first-class plywood. particulaarly for very small boats with thin planking. Really good stuff can just be painted and works fine, although sealing the plank edges with epoxy can't hurt. I think, from my limited experience, that douglas fir marine plywood 30 or 40 years ago was a lot better than what one normally sees today.

Mike in SC
07-19-2001, 03:19 PM
Das reply- one definition of "pig" is: a crude casting of metal. Many boats use lead pigs for ballast. One advantage is that you can move them around to improve trim.

Bob Cleek
07-19-2001, 08:42 PM
Yea, what Mike said. I've always called hunks of raw lead, or iron, for that matter, "pigs" as in "pig iron." I agree that an "instant" boat is deserving of an "instant fix." Heck, just slap some googe on it, as said, and keep the kids happy. It will last long enough for them to outgrow it anyhow. My commendations on your good attitude! (BTW, my first boat was the same!) LOL

Nicholas Carey
07-20-2001, 01:41 PM
Originally posted by Jeff Kelety:
It got me to considering boats like the Shellback Dinghy and the more recent Ellen, though. These are glued up ply boats. No talk of glassing them, just paint and launch, I believe. The Shellback is tauted as a cruising tender, even. Is the difference in the quality of ply? My little dink, I know was built on a shoestring and didn't use marine ply. So can you just paint up good quality marine ply and let it stand in water after painting?

Marine plywood meeting BS 1088 must be the following requirements (off the top of my head):

<UL TYPE=SQUARE><LI>No internal voids are allowed<LI>No veneer patches (maybe minimal patches in interior veneers?)<LI>Type of wood is specified, must be in approved list.<LI>thickness and number of plies are specified.<LI>veneers must sliced rather than rotary cut.<LI>Oh. Waterproof Glue.<LI>the list goes on.
[/list]

As the man said, "Yah gets what Yah paid for."


[This message has been edited by nicholasc (edited 07-20-2001).]

[This message has been edited by nicholasc (edited 07-20-2001).]

Scott Rosen
07-26-2001, 12:48 PM
As others noted, that shouldn't have happened if the bottom were made of high-grade marine ply. I wouldn't bother to glass it, since you have sole boards and there really isn't any abrasion or other wear on the inside of the bottom. Glassing is too much work for this boat. I would strip off the paint and then slather the entire bottom with a couple of coats of CPES. After the bottom is CPES'ed you can repair the blister a la Cleek. Then paint. I'll bet you won't have any blistering problems after that.