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Building a Plywood Shinnster / BRM Paipo

Posted: Thu Aug 24, 2017 3:09 pm
by icedub
Hi All! I'm new to board building and this forum, so hopefully this isn't too dumb of a question:

I'm planning to trace my buddy's Shinn Shinnster and do a simple plywood version. I know this board has pretty decent flex, and having never built a plywood board, I'm curious what this forum might recommend for a good plywood thickness. I can source 1/4" or 1/2" poplar ply from a local distributor. My hunch is that at 160cm long, 1/4" ply will be too flexible, but I'd love to hear from anyone who has built a similar style board!

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Re: Building a Plywood Shinnster / BRM Paipo

Posted: Thu Aug 24, 2017 8:37 pm
by faklord
I know a few people who have done this using two layers of 6mm (1/4") ply laminated together to 'set' some rocker. And then add a layer of glass cloth top and bottom. They ride fine but are a bit heavy. Very smooth on the water (even smoother than a genuine shinnster!) but probably a bit too heavy for flips & tricks.

Re: Building a Plywood Shinnster / BRM Paipo

Posted: Thu Aug 24, 2017 10:07 pm
by direnc
Imo, two 4mm layers should be enough with some fiberglass. If you add a bit of concave, it'll probably be stiff enough with minimal amount of glass.

Re: Building a Plywood Shinnster / BRM Paipo

Posted: Fri Aug 25, 2017 8:47 pm
by icedub
direnc wrote:
Thu Aug 24, 2017 10:07 pm
Imo, two 4mm layers should be enough with some fiberglass. If you add a bit of concave, it'll probably be stiff enough with minimal amount of glass.
Does adding concave make the board stiffer somehow?

Re: Building a Plywood Shinnster / BRM Paipo

Posted: Fri Aug 25, 2017 8:49 pm
by icedub
faklord wrote:
Thu Aug 24, 2017 8:37 pm
I know a few people who have done this using two layers of 6mm (1/4") ply laminated together to 'set' some rocker. And then add a layer of glass cloth top and bottom. They ride fine but are a bit heavy. Very smooth on the water (even smoother than a genuine shinnster!) but probably a bit too heavy for flips & tricks.
Interesting. So using 2 layers just allows you to set rocker into it? I was going to go with the soak and weight method. Hoping that a single sheet of 1/2" will be slightly flexible and not too stiff.

Re: Building a Plywood Shinnster / BRM Paipo

Posted: Sat Aug 26, 2017 8:34 am
by faklord
icedub wrote:
Fri Aug 25, 2017 8:47 pm
direnc wrote:
Thu Aug 24, 2017 10:07 pm
Imo, two 4mm layers should be enough with some fiberglass. If you add a bit of concave, it'll probably be stiff enough with minimal amount of glass.
Does adding concave make the board stiffer somehow?
Yes. But
1) it's quite difficult to build in concave and rocker at the same time, using ply. (I have done this , on a TT, using 3 layers of 4mm ply but it required quite a lot of force and a sturdy jig to hold it in place while the epoxy set...it wasn't great)
2) the ride would likely be quite different to a Shinnster.

Re: Building a Plywood Shinnster / BRM Paipo

Posted: Sat Aug 26, 2017 8:45 am
by faklord
icedub wrote:
Fri Aug 25, 2017 8:49 pm
faklord wrote:
Thu Aug 24, 2017 8:37 pm
I know a few people who have done this using two layers of 6mm (1/4") ply laminated together to 'set' some rocker. And then add a layer of glass cloth top and bottom. They ride fine but are a bit heavy. Very smooth on the water (even smoother than a genuine shinnster!) but probably a bit too heavy for flips & tricks.
Interesting. So using 2 layers just allows you to set rocker into it? I was going to go with the soak and weight method. Hoping that a single sheet of 1/2" will be slightly flexible and not too stiff.
You still get quite a bit of spring back if you set the rocker using 2 layers (more layers, less spring back)

If you can persuade a single sheet of 1/2" to hold its rocker, long term, that should be fine. Personally I think I would still put a layer of glass top and bottom, both to help hold the rocker and also for protection.

One option might be to:
Bend your ply
Glass top surface
Thin out nose and tail sections (using plane/sander)..this will loose a bit of weight & distribute the flex to be more like the genuine article.
Glass bottom surface.

Enjoy

Re: Building a Plywood Shinnster / BRM Paipo

Posted: Tue Aug 29, 2017 1:13 pm
by jannik
If you have access to paulownia wood I think it is a better option. Certainly lighter. I have been building wooden kite surfboards by making a wooden stringer and then glueing wood around that stringer, plane it out, and then trace and cut the outline. Glassing is up for debate. I've used everything from linseed oil to glassfiber felt for walls :) The next few boards will have e-glass on them.

These are build that way:
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P70510-231820.jpg
P70518-070710.jpg

Re: Building a Plywood Shinnster / BRM Paipo

Posted: Tue Aug 29, 2017 5:36 pm
by jeromeL
jannik wrote:
Tue Aug 29, 2017 1:13 pm
If you have access to paulownia wood I think it is a better option. Certainly lighter. I have been building wooden kite surfboards by making a wooden stringer and then glueing wood around that stringer, plane it out, and then trace and cut the outline. Glassing is up for debate. I've used everything from linseed oil to glassfiber felt for walls :) The next few boards will have e-glass on them.
So you get most of the rocker thanks to stringer?

Re: Building a Plywood Shinnster / BRM Paipo

Posted: Tue Aug 29, 2017 9:46 pm
by jannik
I get all my rocker from the stringer. Wood is glued onto the stringer like this
gluing.png
and planed to a blank like this:
blank.png