I found marine plywood!

Mama H Chicago

Mama H Chicago

Mother of sailboats
Chicago is home, but I’m in Michigan this week taking care of my niece and nephew while parents are on business trips…. Lo and behold! I just picked up the two sheets of 1/4” marine plywood I have been trying to source locally with zero success, for months. This is to replace Red Rubber Duck, the 1950’s Sailfish’s deck. Saved myself around $600 in shipping costs!
Now to perfect the art of scarfing them together on plain old cheap plywood before I dare try doing it on my scarce mahogany.
AB44A32C-E675-44EA-898C-758FD0F7785C.jpeg4B9987E3-C441-4064-AE6E-7B61F627FBB4.jpeg4E6A0488-CAD5-45CC-81E2-19EB8F967C6F.jpeg
 
1 inch is all that ALCORT did...as confirmed when we removed the deck and hull panels on our 1963 Sunfish CHIP. Youtubers are blabbing about a 12:1 scarf that is common for a constant angle scarf.
With a LAP JOINT, you'll have a nice straight seam showing.
With a scarf joint you'll get a ragged feather edge.

By the way that BS 1088 (British Standard) is very good marine ply, almost the best. 5 layers of ply vs 3 like you find on average fir ply. And much tighter grain that will not check. Suitable for a bright finish.
 
Aha! Now I understand why the joint is so odd looking! The original seam appears to wiggle all over the place. Mystery solved, and I really appreciate the knowledge before I hit my boards with a hand planer or worse. I feel more comfortable doing a lap joint.
 
Try your woodwork with scraps first. With five plies in only a quarter-inch of plywood, the final finishing/faring of a lap joint can still wander. A quarter-inch of plywood, divided by five equals...um...um...only one millimeter! :eek:

Surely, there's a High School "wood shop" that can handle this cut at no expense for you.
 
Oh I’m definitely going to be trying this many times on scrap first! Great idea about a high school wood shop. My youngest goes to a very very well appointed school. Resources unlike anything I’ve ever seen. I’ll reach out to them too!
 
If you have a router, you can buy an inexpensive router table. Using hold-down fingers and maybe a table extension, you can get very precise cuts.
I rebuilt 3 very old Pella windows, the sill plates had rotted out, and Pella no longer sells them (although they are still in the catalog). I bought a Ryobi router table and a couple of very specific router bits, and 11 passes later, I duplicated the crazy complicated profile of the sill plates. Spent $120 total for table, bits (I had the other bits I needed) and treated lumber. Much better than the 3 grand new windows would have cost me.
 
I built a stand-up paddle board from CLCboats.com and used a butt joint with a backer plate in the flat areas where there wasn't any curve. The material was 3mm okume, I found it very hard to scarf a joint with that thickness so I butted the pieces together and used the same 3mm for the backer plate with about 3in overlap on the joint. It's bright finished and looks great. I also did the same in some spots on a 16ft Malahini design from Glen-L.
 
We cut the lap with a small circular saw with several shallow passes. I think I put another piece of ply nearby to keep the saw flat. Then cleaned up the lap with a variety of hand planes and chisels

lap joint.jpeg


Lap joint 2.jpeg
 
Nice work!

I don't own one of those itsy-bitzy metal block planes. :(

Would "stacking" of circular saw blades have helped move things along? (If possible with your saw).
 
"Stacking" like a dado may have moved things too fast. Smaller cuts = smaller "oopsies."

The thumb planes are fun, as are spokeshaves like the vintage Stanley #51.

Just to confound Mama Chicago more, we have also done scarf joints for the plywood, and we used a belt sander...and finished up with a small palm plane. All four hull panels for a Sunfish hull are stacked here and we cut the at one time. A paint finish was planned so sanding and fairing took care of small irregularities. For a bright varnish fish we'd do a lap joint.

Scarf Belt Sander.jpeg


Scarf belt sander 2.jpeg


The important thing is to NOT trim the sides or the ends until you have a joint amidships that you are happy with. There is just under 16 feet of panel to play with, remembering that they overlap in the middle. If your first attempt is ugly, sit in the Moaning/Learning Chair for a minute and try again. At one point though, you have to use "Would You Notice the Joint From a Galloping Horse?" criteria and continue on :)
 
signal charlie said:
"Stacking" like a dado may have moved things too fast. Smaller cuts = smaller "oopsies."

The thumb planes are fun, as are spokeshaves like the vintage Stanley #51.

Just to confound Mama Chicago more, we have also done scarf joints for the plywood, and we used a belt sander...and finished up with a small palm plane. All four hull panels for a Sunfish hull are stacked here and we cut the at one time. A paint finish was planned so sanding and fairing took care of small irregularities. For a bright varnish fish we'd do a lap joint.

View attachment 55394

View attachment 55395

The important thing is to NOT trim the sides or the ends until you have a joint amidships that you are happy with. There is just under 16 feet of panel to play with, remembering that they overlap in the middle. If your first attempt is ugly, sit in the Moaning/Learning Chair for a minute and try again. At one point though, you have to use "Would You Notice the Joint From a Galloping Horse?" criteria and continue on :)
Click to expand...
I’m now thinking based on the hull, I’m looking at another drive to Detroit to grab two more 1/4” pieces of that lovely 1/4 marine Hydrotek plywood and just practically rebuild this baby. Because I’m a perfectionist and it’s already sold to a family that is so excited to have a beautiful family boat for generations to come.

PS. Can I just send plane tickets to you and/or Skipper to just reassure me that I’m going to be able to do this?
 
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