¼” x ¾” strip plank scarf joint spacing?

Building a Gary Dierking Ulua Nui, sailing double canoe. Hulls scaled up 150% 26” wide & 27” deep, 9’ OAL beam, 28’ OAL.

Because of availability using pretty tight grain Douglas fir quarter-sawn ¼” x ¾” strips.
Have 100 bf cut into approximately 3”x 3-½” x 12’ pieces to finish milling into ¼” x ¾” strips. Should have all finished milled & planed size next week.

I’m using T88 epoxy adhesive (I know not needed) and scarfing the strips 12-1. Will glue scarfs to have 28’ strips ready for planking.

Strongback built, mold stations, mold extensions & cleats made & ready setup on SB.

Because I’m on Big Island HI and we have rocky shores and sharp rocks under water everywhere, will build hulls with multiple layer of S-glass and Xynole a few inches above water line on outside of hulls and multiple layers of S-glass on inside over 5.3oz Kevlar few above waterline.

Glass weave, orientation, weight & number of layers to be determined. Will be back asking about this soon, but that’s the general idea as far as laminates.
Have plenty of buoyancy, so not as concerned about weight as if was canoe.
It will be painted, no bright finish.

Figured I should give some info about the overall build & specs in so have general idea of the project that I’m asking about.

With using T88 glue, 12-1 scarf & DF & the multiple layers of laminated, do the scarfs need any particular length & vertical spacing?

Will avoid scarfs landing on mold stations and will try to keep scarf joints staggered as much as can. But using 12’ long material and cutting to eliminate the odd knot each strip will have a few scarf joints.
Glueing up strips to full length before planking, if not needing to keep a certain distance between scarf joints, will be big help.
If anyone would find build thread interesting, I’ll start one shortly.
By end of next week project will start to finally look like a boat build rather than bunch of mold parts & mostly milled lumber. Lol

Sorry for the long post to ask a simple question, but figured to answer the question would need some info about the build specs.

Cheers, Allen

 

Wow. I do NOT like the thickness of the core at all. When you scaled up; the core thickness needed to increase. You can do so in glass, but the weight tradeoff is not there.

If you have 3/4" finished doug fir and are resawing; you can only resaw at half, so a 1/8" allowance would give you 5/16", unless you plane it to 1/4".

The boat could literally break in half in rough seas if the core is too thin.. Did Dierking sign onto it? I'd trust him.

 

Agree with Fallguy.
Thicken the core.
Remember that the core WILL need to be sanded fair both inside and outside before glossing. It will end up thinner than the strips it is made of.
Adjacent scarfs can overlap.

 

Gary Dierking did the scaling up of the design.
He has had them built to 32’ with the ¼” thick strips.

The Ulua is 18” wide, 19” deep & 18.5’ long in original dimensions with one layer of 6oz glass inside and out, built with WRC usually.

I’m just following Gary’s design, I’m not modifying the design, I asked him about using DF since WRC is difficult to find here and expensive.

Cheers, Allen

 

I started out with three 4x12x12’ beams and
re-sawing and then planing to exact ¼”x ¾”

 

I would mill them fat.
3/8 minimum.
You will lose 1/16 inside and 1/16 outside due to fairing.
They will NOT stack up evenly.

 

I'm about 99% sure you are going to be too thin and the boat will sag across its length dimension when supported on the ends.

I'd be going for 5/16-3/8.

If you stick to the 1/4", make sure the glue seams are lined up edge to edge. But I'd want to be a bit thicker. Some depends on planned use.

I also like to double the glass on the bottom and in the footwells. 6oz can wear ez..