Hey guys,
Just wanted to get an idea of approximately how many builders scarfed their plywood panels together versus using a butted joint with a panel joiner to back it.
Cheers,
David George
P.S.: If you did scarf your plywood, have you noticed any difference?
I used plywood for the but blocks as I felt they would be less likely to split. Other than that, I used but blocks as per the plans.
Butt blocks are easy and are placed so that they aren't in the way anywhere. Plenty strong for this boat, so, unless you want scarf joints for the fun of making them, I wouldn't bother.
I used butt joints without the backing joiner board. I used the invisible butt joint method modified by a suggestion Paul Riccelli made. If you are unfamiliar with the invisible butt joint it is a butt joint with 2-3 layers of fiber glass on each side. Paul suggested that removing the first layer of ply on each side would recess the layers of fiberglass and make fairing the surface a lot easier without reducing the strength of the joint. I did it both ways. The first joint was done before I read Paul's suggestion. It's in the floor of the boat where the nose section joins the rear half. It did took 3 applications of epoxy with filler to fair it smooth. The second joint was in the deck where the nose piece joins with the back half of the deck. I used the recessed fiberglass suggestion and it only took one applicaton of epoxy with filler to fair it. Neither joint is visible after fairing and I feel very confident that the joints are strong enough. I did two tests with scrap pieces of ply and both of the the wood failed instead of the joint line when I bent them to the breaking point. I lso have one small butt joint with a board backing it on the boat. It is in the deck, at the back where the two sides join just in front of the motor well. I used a back plate here because the joint is in the center of a curve and I sanded the backing plate to match the curve radius. I didn't want a flat spot in the center of my nice curved rear deck. Nothing agains scraf joints I just wanted to try the invisible butts after reading about them. Here's a link to a webpage that talks a bit more about invisible but joints:
http://www.simplicityboats.com/epoxyknowhowcarnel.htm
I thought if the joint was good enough for Carnel, Payson and Riccelli that I would risk it.
I scarfed together the bottom, to avoid the panel joiner in the cabin. For the deck I used all panel joiners, but made them of magony with rounded edges if the would show.
Dave
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Shown on top of these two pieces of joined plywood is my way. On the bottom is the way most every one else tells you to do it. The heavy line represents the cloth, the dark area the filler. You decide which you'd rather work with and which is easier to fair smooth.
I've used this method Paul on my kayaks, works great and is neat.
My version has several advantages. It can be "cast" in one shot, once you get the hang of how much material to use, leaving nearly perfect surfaces. It's stronger then any other method (pound for pound), it's lighter, requires no fasteners (though temporary screws might be used), you don't need extra bits of wood, which also need to be cut to size, sanded smooth, edges rounded over, etc. I can't see why anyone would want a butt block joint, other then traditional construction repairs, where keeping the repair the same as the rest of the boat is important.
I think I like the vertical butt block in the hull sides, because it may add some stiffness to the structure in that spot, it's right where the boat hits fenders and stuff, so I feel the block is more of a frame member. But I would have liked to do Paul's method on the cabin floor/sole, that butt block doesn't serve any ancilliary purpose on the boat.
I have to correct myself. I used butt block joints in the sides where the two ply pieces join as well as the small rear deck one. I did it because the plans call for oarlocks in that area and I intend to add a brace there to support the cockpit edge of the deck. The cockpit is almost 7 feet long and though the bench coming across adds some support and 1x3s, glued and screwed along the bottom edge of the deck around the cockpit, add significant stiffness I worry that the 3/8" ply might flex.