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Convertible challenge

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BWD
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Convertible challenge

Postby BWD » Sat Aug 18, 2018 12:47 pm

I’m building a new hybrid/convertible board, outline is paipo-ish, about 145 x 48, 10-12cm nose rocker.
Expected use 2/3 foiling, 1/3 planing.
Corecell and carbon.
The center will be stiff from foil mount to front foot.
I want flex in the ends. Not a lot, just a bit.
Rider weight range 75-85kg.
To any carbon experts around, how thin do you recommend I make the core in the flexible parts of the board?
9mm? Less? The blank is 20mm max. and I’ll keep this thickness through much of it for central stiffness and float...
Planning to use 2 layers hexcel as4 6oz 0-90 13x13 plus reinforcements for foil foot and fin areas.
Also have some unidirectional I can apply for extra longitudinal stiffness etc.
I have a few ideas (including adding some glass or cf on bias or 45/45 biaxial to mix), but curious how others would approach this project...

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Re: Convertible challenge

Postby rynhardt » Sat Aug 18, 2018 1:20 pm

Using 200gsm spread tow carbon @ 0deg on a TT, core can be 7mm centre tapered to 3mm at the tips. That's for a flat board with 5cm static rocker (each end) on a 140cm board.
With 85kg on it the rocker will go down to about 2cm.
Add concave and it gets stiffer.

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rynhardt
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Re: Convertible challenge

Postby rynhardt » Sat Aug 18, 2018 7:37 pm

Actually just finished bagging a board tonight. Spread tow carbon on top, glass on bottom.. Gonna be interesting to see how the flex turns out..
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Re: Convertible challenge

Postby BWD » Sat Aug 18, 2018 7:43 pm

I’m thinking mine will either end up with some glass or bias oriented cloth to get just a bit of flex...

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Re: Convertible challenge

Postby fluidity » Mon Aug 20, 2018 10:56 am

BWD wrote:
Sat Aug 18, 2018 7:43 pm
I’m thinking mine will either end up with some glass or bias oriented cloth to get just a bit of flex...
I've just done a semi infusion :o of a twintip with combined uni glass 150mm 850gsm top and bottom and double bias 650 gdm full width top and bottom over 10mm foamcore. Slower hardener next time!
I'm going to try to infuse the rest at some stage, seems a pity to waste it and I don't think the infusion seams will seriously compromise the strength.
But anyway, it's got about perfect flex for what I wanted. If you are going full carbon then you will have to go thinner than 10mm for any significant flex.
If you want to compromise then I'd recommend carbon on top with triaxial or part of it unidirectional along the long axis and unidirectional glass underneath with some carbon biaxial as the outside bottom layer.
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BWD
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Re: Convertible challenge

Postby BWD » Mon Sep 10, 2018 5:08 pm

I have had the convertible project on the back burner for a while, but getting ready to laminate.
I have been thinking of applying the 6oz carbon twill at 45 degrees to get strength, reasonably light weight and ability to tune flex with 0-90 patches and some uni, so the board will ride ok without the foil. I don't want it too rigid for enjoyment as a conventional board.
I have not seen this done very much though, applying 0-90 cloth on the bias to get 45/45 fiber path.
Is there any reason, other than "inefficient" use of cloth?
I have reinforcement patches and some small parts/projects in mind for the leftover triangles of cloth, so I don't see it as a waste for a one-off.
Any thoughts?

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Re: Convertible challenge

Postby rynhardt » Mon Sep 10, 2018 8:29 pm

BWD wrote:
Mon Sep 10, 2018 5:08 pm
I have had the convertible project on the back burner for a while, but getting ready to laminate.
I have been thinking of applying the 6oz carbon twill at 45 degrees to get strength, reasonably light weight and ability to tune flex with 0-90 patches and some uni, so the board will ride ok without the foil. I don't want it too rigid for enjoyment as a conventional board.
I have not seen this done very much though, applying 0-90 cloth on the bias to get 45/45 fiber path.
Is there any reason, other than "inefficient" use of cloth?
I have reinforcement patches and some small parts/projects in mind for the leftover triangles of cloth, so I don't see it as a waste for a one-off.
Any thoughts?
We generate a fair amount of waste. Our 200gsm alutex is 0/90 on the roll but we use it +45/-45.
And our 410 biax glass is +45/-45 on the roll but we use it 0/90. :o
Crazy, but it gives us the flex we want.
I have lots and lots of waste triangles :-?

PS. just be careful with patches with straight edges - they can cause stress risers at the edges. I've seen some guys feather the edges to compensate.

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Re: Convertible challenge

Postby BWD » Thu Sep 13, 2018 5:35 pm

update below....
Last edited by BWD on Mon Apr 15, 2019 6:45 pm, edited 2 times in total.

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Re: Convertible challenge

Postby BWD » Mon Apr 15, 2019 6:44 pm

Finally got this project done in small stages over winter in living room, kitchen and patio.
Could have taken 6 days instead of 6+ months if I had a workshop. Maybe.
144x49x2.3 rocker about 10cm, touch of tail rocker, soft vee bottom, max ~2-3mm in rocker entry.
Foil mount centered about 37cm from tail, per foil maker (Ketos) specification. This spec was a design consideration from the start.
IMG_2405.JPG
Construction from deck down:
1. 200gsm hexcel as4 carbon twill 0/90 patch ~25x12cm over foil mount area
2. 200gsm hexcel as4 carbon twill patches over stance area, 0/90 over central 22cm, 45/45 over outer part, no rail wrap
3. 200gsm hexcel as4 carbon twill 45/45 overall, free-lapped
4. 200gsm hexcel as4 carbon twill 0/90 patch from finboxes to nose rocker kick, V tapered, free-lapped
5. 20mm corecell A500 core, 3mm X ~70cm center okume stringer in stance/foil area, 2 3mm X ~15cm okume mini-stringers around front edge of foil mount, 4 futures fin boxes, leash plug, 25mm diameter high epoxy/high density filler foil mounting plugs
6. 227gsm hexcel ga060 unidirectional carbon, 3 strips total width ~12cm
7. 200gsm hexcel as4 carbon twill 0/90 patch from finboxes to nose rocker kick, V tapered, free-lapped
8. 200gsm hexcel as4 carbon twill 45/45 overall, free-lapped
9. 200gsm hexcel as4 carbon twill 0/90 patch over foil mount area, ~18x60cm
10. 200gsm hexcel as4 carbon twill 0/90 patch over foil mount area, ~16x45cm
11. 200gsm hexcel as4 carbon twill 0/90 patch over rear finboxes (because they extend aft past layer 7)
Total about 2.45 m^2 of the 200 gsm twill, plus about 0.125 m^2 of uni.
Resin Research Quik Kick epoxy.
Result: 3040g raw board, about 5875g with ketos 1200/71cm mast (2.45kg)/plate adapter(360g), screws & gasket, hexatraction.

Board trialed with foil and through bolted hardware and with fins. Will eventually get foil mount inserts installed from deck.
It will also get one through-hole to allow removing the foil with a single screw while the plate stays on the board.
I rode it in surface mode with 4.5" glass front fins and ~4" foam-cored trailers, screw holes covered with surf wax.
Conditions were 10-16 knots, one flat water session and two with 30-70cm ocean waves and light chop, kites 9 and 12m BRM C2's.


First impression is the board did well riding with foil and with fins.
The balance point over the wing is really close to center of pressure for surface riding, so somehow it seems like the same board, on or off foil, more than my old convertible paipo. It carved nicely and held great -- I might try it with smaller trailers for a slashier ride some time.
I thought of tapering the tail and nose thickness a lot for some flex there in planing mode but decided I would rather preserve the volume (~13L), since my old paipo foilboard at ~9-10L just didn't float as well as I like. The slightly vee bottom shape helps make riding such a stiff board on the surface in chop an acceptable compromise, and seems good in touchdowns -no rail catch so far. It does have just a little flex, in the pattern I was after with the laminate design.
On foil the board seems well balanced and very responsive to me, but admittedly this is in comparison to bigger boards and heavier foils. I could say more after I ride it more.
The large, light wing often held board floating on edge for 10-20 seconds, great for spotting it right after a fall.
Then it would settle down and float downwind. Didn't have the board sailing away upwind problem, so far.
It's pretty well balanced with the foil I used, making waterstarts and handling easy, and the length is just enough to be ok as a surface directional for me.

Eventually it might be nice to have higher volume lightwind/foilsurfing and shorter, lighter kitefoil-only versions, with integral mastboxes to save weight.
Right now having a convertible to save space and a plate to give me a few extra cm mast height seems good though.
Probably some shortcomings will emerge after more sessions, but so far I am happy.

I was shooting for 3000g and almost hit it, with all high-density core, quad boxes and plenty of strong carbon. And no vacuum.
The lamination schedule did end up a little weird/complicated to get what I wanted from the available cloth I had, some of which came from odd shaped offcuts.
Lighter core, less boxes, slightly simpler lamination schedule and/or vacuum techniques could easily drop 300-500g off this, even at the large size (~5850cm^2)...
It's been a fun project, even without a proper work space.
Now the real fun begins with summer riding coming and I will see if I remain pleased or join the convertible naysayers.
I have a suspicion I won't and the reason may be that many convertible boards weigh a kilogram ( or 2 :o !) more.
We'll see...
IMG_6947.JPG

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Re: Convertible challenge

Postby TomW » Wed Apr 17, 2019 7:49 am

Nice work!

But be forewarned.
Once you try a 120-90 cm foil board, 2 to 2,2kg , you'll never want to ride a 145 cm board that weighs 3kg.


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