Stringer in small foilbord?

[bay surfer]

Thanks TomW - did not mean to wind you up...

Also thought about getting this track box - https://www.mackiteboarding.com/ride-en ... track-box/
Available June 2020.

you can buy that. It will save work. Other option is to buy the boxes separate and get some HD foam and build it yourself. You might save 30-40 dollars if you shop around.
building it yourself is easier that the process of adding stringers and then the boxes. The stringers are not going to replace the need for HD foam anyway.

Im in EU, so i buy BigHeads from EasyComposites in UK. Then i embed 4 of these in HD foam blocks in fixed position. Im riding strapless and know where the foil should be on board, so no need for adjustment.
The Bigheads cost 2.20$ each. So 9$ a board.

You can buy a track box embedded in HD foam from AliExpress for about 20 USD.

Good luck with with getting things from China, 2 months wait so far for foil boxes!

[Kiterpep]

What about a longer foilboard, e.g. 130 cm? Can you still get away without a stringer if the lamination is strong enough?

[TomW]

What about a longer foilboard, e.g. 130 cm? Can you still get away without a stringer if the lamination is strong enough?

Yes, you can build any length board without a stringer....

[dirk8037]

As most said, I am also convinced that it is not necessary. I think tha even the layer setup of most is exagertated if you put patches wisely.
See the Gong Flint setup - Sandwich with 80gr glass inside and 200gr Carbon outside.
The power distribution from the Mast is essential. I guess a broad connection with the top is mandatory.

Depending on your skills load might be different.
Touch down will cause tension on the bottom, Carbon UD, and compression on the deck - added thickness like PVC or wood inserts might be the call.
For cruising the bend down by your wight on the front foot does definitely not require multiple layers of Carbon.
Rather thicker UD Glass on th upper most outer keel lines, if you have chimes and concaves.
Jumping will be more the oposite.

The rest is nothing, heel pressure does not exist, torsion from mast to board yes but since the board is in any way light wight there is not that much of torque. So if its set into the board nicely and the load distribution in a radius of 30/40cm is good (also below the sandwich)
Board ot driver - well - how much you knees and ankle will take. I rather give way - so its neglectible.

Saying that, I did it all different this summer with a 130x50 cm board I made out of scraps.
3cm 15kg EPS, with 2mm core cork on th button and 3mm airex on top each 80gr below.
Since I had a lot of balsa cuttings I made a 1 cm Stinger that connected with the plate base and 1.5 cm of outline stringer. (3x5mm layers laminated - kind of like firewire)
Both connected with 2 tip/tail blocks.
Above all 200gr + 50gr on top on both sides and added patches for feet and mast base.

If you would be more routined with glassing than I am, you can come out below 3kg.
Eg use PU glue for balsa to eps instead of epoxy and bubbles.
Propper Vakuum that sucks out the exess resin.

As I am far away from jumping it seemed to me more that stable enough
Pre lamination the whole thing seemed so solid that even a 160/50 job on both sides would be ok. Patches for Mast yes, for feet no, better a double sandwich at those spots.


Cheers Dirk

[thewindego]

I have boards that are now on their 2nd season with 2 different riders who basically ride all the time. The construction was corecell 80k/m3 20cm. laminate is 600gm/m3 twill both sided plus generous unidirectional where it counts and another patch under mast. Vacuum bagged with peel ply and release fill film and rails wrapped...difficult. Inserts through to deck. The 110x45cm came in at 2.1kg with a spray traction deck.
I finished with lots of wet sanding and finish spray urethane clear. Too much time finishing but the naked carbon it too nice to cover up IMO.
So looks like overkill but lots of miles and jumps and no problems.
I may get some lighter carbon and see if I can cut the weight a bit. Not sure at 2.1kg it matters though. The bomber build is probably worth more in the long run.
Oh ya no stringer.

[TomW]

kiterpep,

Don't get too wrapped up in all these complex descriptions. For a 130 cm foam core board there are some simple principles.
Aways use same laminate top and bottom. Symmetrical.
With high foam density around 60-80 kg / m3 you can get away with thinner laminates.
With thicker blank , over 35mm , thinner laminates.
The lower density foam requires thicker laminates to resist heel dents.
If you post what density foam and thickness you are thinking, I can recommend a laminate schedule.

Notes:
heel dents are an issue in hydrofoiling boards.
Deck laminates are super important because of both heel dents and the fact that you have body weight plus power of kite through the top laminates.
Bottom laminates resist crushing/ compression forces at mast plate and slams upon grounding.
600g cf on 80 kg foam is overkill, but ok, board will last 50 years.

[Jyoder]

How much 280g uni D CF should I put under the 200g twill CF on a 110cm strapless board with core of 20mm 80kg Divinicell?

Full length uni D? Multiple layers staggered?

Will have some extra twill patches on pressure points.

I need maximum Strength/stiffness as I ride race style at times.

Thanks,

[thewindego]

The one rider of that pictured naked carbon I posted he calls his forever board the black pearl.

Tom when you finish your 110 with 20mm pvc I will be interested to see where your weight ends up compared to my overkill layup, I figure the one 600gm layer per side well vacuum won't really cost that much weight more than 200 and patchs since the foam still needs to be wet out and of course the finish.

[Kiterpep]

kiterpep,

Don't get too wrapped up in all these complex descriptions. For a 130 cm foam core board there are some simple principles.
Aways use same laminate top and bottom. Symmetrical.
With high foam density around 60-80 kg / m3 you can get away with thinner laminates.
With thicker blank , over 35mm , thinner laminates.
The lower density foam requires thicker laminates to resist heel dents.
If you post what density foam and thickness you are thinking, I can recommend a laminate schedule.

Notes:
heel dents are an issue in hydrofoiling boards.
Deck laminates are super important because of both heel dents and the fact that you have body weight plus power of kite through the top laminates.
Bottom laminates resist crushing/ compression forces at mast plate and slams upon grounding.
600g cf on 80 kg foam is overkill, but ok, board will last 50 years.

Thanks for the advice. I am thinking of the following:

- 20 kg/m3 EPS 4 cm thick, this is what I have here already and what sparked the idea for the project,
- 80 kg/m3 1 cm high density foam in standing area (replaces 1 cm of EPS so total thickness still 4 cm). Strap inserts and foil track box are also in HD foam,
- Lamination symmetric, for sure
- Bottom to top: 20 cm uni carbon stringer 200 g/m2, 240 g/m2 carbon/kevlar twill reinforcement above foil box, 240 g/m2 carbon/kevlar twill full board, 200 g/m2 glass full board. Rails wrapped double.

-> I chose the carbon/kevlar twill because I liked how it looks and for the impact resistance of the kevlar.
-> Glass on top so that I won't have to sand any carbon (unhealthy) or kevlar (difficult because of fraying). I do understand that from a structural viewpoint the glass on the inside would be better.
-> Shaping blank with hot cutter. Want to shape the rocker in the foam.
-> Vacuum inside a clothing storage bag.
-> Wanted to do the deck first with peel ply to get a rougher finish for bonding next layer on rails and deck pad.
-> Then bottom with perforated release film to get a smooth finish.

? Is there a particular reason the bottom is usually laminated first? On surfboards it makes sense since the deck is doubled but not the bottom, but with symmetrical lamination I don't see why I shouldn't do the deck first?
? Also wondering if a hot coat is normally necessary after vacuum bagging. I would guess not, but experience here is appreciated.
? Recommendations on the rocker for a 125-130 cm board are also appreciated. Was thinking of something like 8 cm, but I've seen and read that even more is better?

[TomW]

Kiterpep.

That laminate schedule sounds reasonable, but put the same uni d and twill reinforcement on the bottom too. Putting glass on as sacrificial layer for sanding is a good idea when you are new at it. It will help with ding and heel dents but won't add any stiffness to the board.

Laminating bottom first is just a convention, but it can be easier to sand the laps by doing deck last.

After you have laminated, you'll want to brush on a sanding layer of clear epoxy. Then sand this smooth with 120g paper. Then do another coat on bottom and rails ( you might have to tape rails and do it in 2 steps) and sand this 180-220-400-800 for Matt finish or continue to 1000-1500 and then Polish compound for gloss. I usually do matt finish. You do all this wet sanding and you gotta be careful to not sand through.
Finally I tape off deck and brush on epoxy and lay down peel ply for textured deck. I don't have to do finishing layer on the deck, but I do do sanding layer and then peelply texture layer.
I've never taken the short cut of not doing the sanding layer. Might work.

Rocker of 80mm should be good. Think about making it fairly gradual, not a "L" shape , kicked nose.

One other thing, your deck HD foam could be 3mm, with a layer of glass under. That's normal approach. 10mm is really thick, do putting glass under is not really going to do much.
Good luck. Best thing now is to get out and shop and start making mistakes. Learning