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.
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