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DIY split wave twinny

Posted: Sun Dec 03, 2017 7:17 pm
by rynhardt
Last year I built a wave twintip which was pretty much a shameless copy of Nomad's wave twinny's, at least on the outline.
It has become my favourite board, bar none.
However, I really really dig the convenience of travelling with a split board.

So, logically, there can be only one conclusion.. I have to build a split version of my wave twinny. :D

Some requirements:
* Fit in a suitcase with inside measurments of 76cm x 50cm
* Bindings (boots) compatible
* Grind base (so I can do beach starts with the boots on)
* Retain the flex characteristics of my other board where possible

Given that this is my first attempt at a split board, I wanted to keep things simple, but robust.
Doing a bit of Google-fu, I finally decided to use the plate approach, also known as a strapped butt joint.
This seemed the easiest to fabricate and would allow the most flexibility in terms of adjusting the flex after the fact, by changing the plate.
Also, the plate approach allows you to fit a longer board into the suitcase, as the W-joints take up another few centimeters.

To test the characteristics of the stapped butt joint, I screwed 3 pieces of foam together and bent it both ways.
What I learned from this is the where the two plates overlap, the structure is as strong as both plates together, if not stronger.
Where the top strap terminates on the bottom plates, there is a definite stress concentration, unless the top strap is tapered.
In the middle where the butt joint is, the top strap does all the work.
Some of these conclusions are more obvious than others :-)

Re: DIY split wave twinny

Posted: Sun Dec 03, 2017 7:23 pm
by rynhardt
The basic board design was an exact copy of my old board. 146 x 46 elliptic outline.
ABS rails and spine, with inserts embedded in the spine.
Add to this some additional ABS in the middle where I was going to cut the board, plus inserts embedded in the ABS.

Re: DIY split wave twinny

Posted: Sun Dec 03, 2017 7:33 pm
by rynhardt
Board was built using vacuum infusion on Kerry's rocker table, which has a bit of concave.

Layup is from bottom to top:
* Grind base (0.8mm isosport 6000 cross-linked)
* 100gsm glass (0/90)
* graphics (polyester fabric)
* 200gsm alutex (-45/+45)
* 410gsm biax glass (0/90)
* Core (abs and divinycell H80)
* 410gsm biax glass (0/90)
* 200gsm alutex (-45/+45)
* graphics (polyester fabric)
* 100gsm glass (0/90)
* peelply
* flow mesh

I've come to rather like the matt peelply finish, and it is just so easy to do.
Simply peel of the outer layer once the board is baked and you're done :-)

Re: DIY split wave twinny

Posted: Sun Dec 03, 2017 7:44 pm
by rynhardt
So far, so good.
Next up was to build the top strap (plate).
I masked off the middle of the board, put down some peelply and did a wet layup on the board.
This was to ensure the plate would conform to the deck shape perfectly.
The wet layup was spread tow carbon on top and bottom, with glass inside tapering from about 2mm at the edges to about 8mm in the middle.

Once everything was done and put through the post-cure bake, I made a template of the mounting holes on mylar, and drilled corresponding holes into the plate.
I was careful to offset the holes 1mm closer on the one side, which is the width of the blade used for cutting the board.

Re: DIY split wave twinny

Posted: Sun Dec 03, 2017 7:49 pm
by rynhardt
The most nerve-wracking part of the process was next.. cutting the board in half! :o
I used a jig saw with a very fine blade, and cut about 2cm at a time, cooling the blade as I went.
Apart from taking a long time, it was disturbingly easy. :lol:

Re: DIY split wave twinny

Posted: Sun Dec 03, 2017 7:53 pm
by rynhardt
Last little bit was to trim the edges, clean up the holes and mount fins.

Below are closeups of the plate and the bottom, showing the concave and also the cutting line.

Re: DIY split wave twinny

Posted: Sun Dec 03, 2017 7:54 pm
by rynhardt
And finally... the end result! :D
It does also fit into my suitcase :thumb:

Re: DIY split wave twinny

Posted: Sun Dec 03, 2017 8:02 pm
by rynhardt
The old board (same size and layup) was 3.0 kg.
The split board is 4.6 kg (deck + plate).
The deck itself is 0.8kg heavier than my old board, this is due to the additional hardware as well as the grind base.
The plate is 0.8 kg. I think I overdid the plate a bit, so I might drill some holes in it to make it lighter at some point.

But the next step is to go and abuse it at the cable park and see if anything breaks!

Re: DIY split wave twinny

Posted: Tue Dec 12, 2017 5:51 pm
by rynhardt
Just returned from an awesome session today at Langebaan. Was on my 6 and my new split wave twinny. Am super stoked with it!

Re: DIY split wave twinny

Posted: Tue Dec 12, 2017 11:35 pm
by TomW
Nice work. I've been thinking about making a split hydrofoiling board.
I was thinking a plate on top and bottom.
The one on the bottom would extend under the hydrofoil mast plate and forward and the one on top would be flush with the deck pads, but only in the middle like your plate.

My board will be made with foam Core

Have to think about it.