MARINE PLYWOOD JOINTS

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Jeff P.
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Joined: Fri Sep 17, 2004 8:49 am
Location: Woodstock, IL

MARINE PLYWOOD JOINTS

Post by Jeff P. »

Hi I'm a first time boat builder, but avid woodworker. I've recently begun building a Zip. My question is concerning the plywood used for the hull. I would like to use Ribbon sapele Mahagony but can only find it in 4 x 8 sheets. Which is fine, but I'm worried about the "look" of the hull with a vertical joint line. (I'm planning on painting the hull only below the water line). On the other hand I can find Okuome plywood in 4 x 16 sheets. No joint line but I'll be losing the grain pattern. I'm looking for opinions concerning this joint line and how to disguise it. When finished, my boat will look similar to the one made by Robert Pinske, Oliver, BC (2-03).

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DavidMcA
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Post by DavidMcA »

Idea 1>>
If you plan to use a butt joint with a backing "butt block", you could epoxy and screw it all together on a flat surface, then remove the screws once the epoxy is set. Then you could slightly drill out the holes with a half-inch spade bit and epoxy mahogany plugs into the holes.
Idea 2>>
Or if you don't want to use screws at all, you could again assemble it on a flat surface, position it with a couple of small brads and use bags filled with sand to clamp it until the epoxy cured. You'd have to make sure the whole thing didn't slide all over the place though.

If you mix some fine mahogany dust with the epoxy you use to glue the butt joint together, it will result in a dark glue line which tends to blend into the mahogany which naturally has black flecks in it. Other than that, just make sure that the joint is as tight as possible.

Personally, I think I would use Idea 1 because I'm sure there would be a lot more similar plugging to do in other places so it would be a relatively easy thing to do. And I'd also go with sapele rather than okoume....much nicer grain. I used sapele on my decking and where the sections butt joint, the different grain patterns make it more interesting to look at. So long as the joint is not massively wide, you're gonna be looking at the beautiful grain and not the joint!
David McAdam
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kens
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Post by kens »

I would look into the scarfed plywood joints. I believe that when you purchase long sheets, they are really just factory scarfed anyway.
I have practiced Marine Fir ply scarfs, and I can get the glue line to nearly go away.
A proper & tight scarf doesnt bother me anymore, since I been practicing.
If you can get lucky enough to find similar grain patterns on both sides of the scarf, the glue line may dissappear, or at least be so fine as to be quite acceptable.

Practice this: go to the scrap bin and pull a strip of ply. Cut it in half.
Then scarf it back together with a GOOD scarf.
From 15 feet, the scarf will go away. Looking at the edge of the plies, the scarf will go away at arms length.

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Dave Grason
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Post by Dave Grason »

kens wrote:...I believe that when you purchase long sheets, they are really just factory scarfed anyway....
You're correct, Kens. My Zip has factory scarfed joints in the Okoume and they ARE definately visible, although the scarf work done is very strong and certainly looks seaworthy. I think though that the factory used a filler that was a little bit different color and that's what's making the joint so obviously visible.

Sometime back, Wooden Boat magazine ran an article on how to make a scarfing jig using a circular saw. I read the article several times over and it seemed simple. But now I cannot for the life of me, find that issue. We moved and I think that this particular issue may have inadvertantly hit the trash. I went to Wooden Boat magazine's website to order the back issue but none of the back issues have any mention about a scarfing jig in the descriptions. If anyone knows which issue has this article, I'd sure like to know. I really want to build one of these jigs.
Isn't it amazing!! The person that never has the fortitude to pursue his own dreams, will be the first to try and discourage you from pursuing yours.

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Graham Knight
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Post by Graham Knight »

Dave, there's a website that shows how to do this too but I forget where, a Google search for "plywood scarf joint" should find it. It was a baotbuilders website, may have been kayaks I think.
Graham in Shepperton, England

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Doug N
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Joined: Thu Dec 04, 2003 11:10 pm
Location: Fort St. John, British Columbia

Post by Doug N »

One website for scarfing is
http://www.tracyobrien.com/article.asp?a=show&id=2
Another is
http://www.duckboats.net/scarf.htm
Hope this helps.
Doug

Jeff P.
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Joined: Fri Sep 17, 2004 8:49 am
Location: Woodstock, IL

Thanks for the Info

Post by Jeff P. »

I would like to thank everyone who answered the topic I posted. I haven't yet decided which type of joint I'm going to use yet (ie Butt or Scarf). This discussion has put my mind at ease over the look of a vertical joint line though. Thanks.
Here is also another web site showing a jig for cutting a scarf joint.

http://www.oneoceankayaks.com/stitchglu ... rfjig2.htm

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Graham Knight
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Post by Graham Knight »

That's the one I was thinking of Jeff, although I'm leaning towards a router jig as the easier method now! I have circular saws, routers, and power planes so I have the choice, for narrow strips (as in clinker/lapstrake) I think the router may be best, for wider stock perhaps the planer.
Graham in Shepperton, England

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Dave Grason
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Post by Dave Grason »

Thanx to Doug and Jeff for those websites. Good stuff.

The jig shown at "oneoceankayaks" is identical to the jig in Wooden Boat magazine. I'll now be able to build what I want.
Isn't it amazing!! The person that never has the fortitude to pursue his own dreams, will be the first to try and discourage you from pursuing yours.

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