Stitch and Glue Ply Selection

[craigbalsillie]

When I first came upon the idea that you can build a very decent boat at home using this method I figured it would involve the purchase of decent quality marine ply. I have done a bit of digging and have found that standard external WBP ply does the trick just as good, since it all gets covered with the Epoxy Resin thereby rendering it waterproof (unless I'm mistaken in which case I'm sure you'll let me know). If I am right though, then are there any reasons why you couldn't use sheathing ply?
It's available in the same sort of thicknesses as External WBP and if you intend covering it all with Epoxy and painting it rather than having the lovely wood grain showing I can't see the problem. Strikes me that would make the building of a home brew even more economically viable.

I've been wrong before though,!!

<hr width=100% size=1>

 

[Stemar]

Bateau.com argue this, and it's true if you can guarantee that you'll never give your pride and joy a ding that will expose the wood.

A good quality exterior grade ply (BWP) will use the same glues as marine ply, but there will be fewer, thicker plies and you will find a few voids. This will make it a bit weaker and, if you get water into a void, next to impossible to dry out.

If that doesn't matter to you, then, imho, you should be OK. I'm tempted to build Bateau.com's 4 dink as a tender, and I'd use bwp ply as it'll probably have a fairly hard life, being dragged up and down slipways, so I wouldn't expect it to last for ever anyway.

<hr width=100% size=1>

 

[VicS]

I made a small dinghy 25 years ago from wbp using the stich and glue method. Its not completly coated but (regularly) varnished inside and painted outside. It spends every summer upside down on the sea wall but I take it home and cover it up for the winter. It still looks as good as new!

I also built a Mirror and a canoe using this method. With the smaller ones you can use Nylon fishing line to stich them together with just copper stiches at strategic points. After taping the insides of the seams you cut away the stiching from the outside before taping those anyway.

Be sure you get good quality wbp though. The cheap stuff I used for a camping trailer has delaminated.

<hr width=100% size=1>

 

[johnsomerhausen]

I built the nesting dinghy the plans of which appeared in a 1989 issue of PBO.
Considering the time and effort I was going to put in the project, I thought it more cost-effective to buy good plywood and went in for Bruyzeel mahogany ply. In one respect, it would have been better to go for the cheapere and more flexible Okoume ply: there was a certain amount of twist in the bow which gave me a bit of trouble (I am the typical non-carpenter and all thumbs...). The plywood was covered with epoxy and then painted with International paint. It is still holding well after more than 10 000 miles on the cabintop of the boat, a few dunkings and scraping on rocks and slipways.
john

<hr width=100% size=1>

 

[drawp]

Craig. I know there is a big difference in price between marine grade ply & WBP for (in my mind) small difference in quality. How does the difference in price between WBP and sheating ply compare? I built a stitch and glue dinghy a couple of year ago using bog standard exterior grade ply and the biggest factor in the cost was for the epoxy. Where do you get your epoxy?

<hr width=100% size=1>

 

[craigbalsillie]

Peter,

I haven't got as far as sourcing any Epoxy as yet. I was going to try Duncan's the chandlers in Glasgow but as there are a few places along the clyde that build/repair/restore boats I'm sure I shall be able to get some.

The quality of sheathing ply is poor. It's the sort of stuff builders use as a base for putting roofinf tiles on, or local authotiies use to board up windows in disused properties. The thing that concerns me most is the amount of knots you get in sheathing ply. But if it;s going to be completely covered in Epoxy I don't see that this should be of any concern.

Thanks to all who have contributed so far.. as usual it's all good advice..

cheers Craig.

<hr width=100% size=1>

 

[JBofBideford]

You may find that cheaper ply has less well-sanded surfaces, which means it will take up more epoxy to seal and fair it. I built Bateau's D4 dinghy with external ply, but used much more epoxy than I was advised it would need due to my inexperience, and I found the epoxy very expensive compared to the cost of ply for the project. On reflection I'd use better ply next time, and hopefully less epoxy.

<hr width=100% size=1>