Next: a displacement hull SUP ?

Last summer I built my first board, an 11 foot SUP. I got a lot of good advice here and I am pleased with the way it turned out. It looks good, performs well, and it’s sturdy. It’s a good first board.

I use it in choppy water (the Niagara river) and the chop is a bit of a problem: when I meet waves head-on, the tip of my board digs in and slows me down. It’s planing design - a rounded bow.

So I am fantasizing of board #2, a long, lean, displacement hull design. Narrow and pointy up front.

Which brings me to two questions.

  1. Where can I find a design or a sketch to use to shape my EPS?

  2. I have a 12 foot by 3 foot by 6" block of EPS. I would like this board to be a bit longer, maybe 13 or 14 feet. Can I scab on another piece of foam? What effect would that have on strength? I mean, what portion of strength comes from the EPS vs the laminate? I could probably insert a couple of wooden dowels as stiffeners - like rebar in concrete. Should I do that? Or would another layer of glass around that joint provide all the strength I need?


But my first sup was just glued together from 4 3 foot blocks, and I think the glue joint is stronger than the EPS itself. So just add a piece of EPS and proceed as usual. No extra glass needed at the joint. In my opinion…

Ha ha! What a perfect answer! Thank you!

Did you use construction adhesive?

I used some kind of fix it all glue- soudal if I remember. I just tested if it’s possible to hotwire after glueing. I am pretty sure you can find better glueing solutions here on swaylocks, but that worked for me.

Hi Leecallen,
For scabbing EPS, my favorite is Gorilla Glue (foaming polyurethane). Epoxy works too. Some people tried 3M#78.
Regular white Elmer’s Glue does not work. I would not take PL200 or any other caulk gun construction adhesive stuff to a board.
The glue line will be harder than the foam so care needs to be taken shaping in those areas.
Also have adequate ventilation while hot wiring glued-up materials, you don’t want to breathe burnt styrene and isocyanates.

As far as the design goes…I would not expect anyone to provide me ‘the keys to the church’ in one sitting.
-go to shops, talk to the people, look, feel, take test rides
-research online, study the pictures
-use 3D models for inspiration/information (like if you have a login for Shape3D Warehouse or someone sends you an example)
-make sample pieces . I did this for my first ‘boatnose’ SUP and then got feedback from other builders. See pic below
-look at sites dedicated to SUP and SUP shaping like The Shape Shack

Back to scabbing…enclosing some pics of a scab operation on a SUP. Note the two types of glue lines: one that is almost invisible at the stringer and one that is exaggerated for the sake of the colors at the scab. I also consider where my vents will be on a scabbed board and make provisions to equalize pressure between glued pieces such as drilled holes or small unglued sections deep in the board. Also showing a practice piece for ‘sussing’ out a boat nose.

jrandy, that information is incredibly helpful.

The tips you gave about board design - yeah, that’s more or less the way I did my first one. I looked at lots of boards, and then I copied one I really liked, and then fine tuned the shape a bit to fit my preferences. I was hoping to find a shortcut this time around.

But I will follow your advice re: research. I especially like the idea of building a model first. That seems like a no-brainer, but I didn’t do it on my first build, and things would have been easier if I had.