Forums > Kitesurfing Foiling

Twintip to Pocket Board Conversion

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Created by djdojo > 9 months ago, 16 Dec 2018
djdojo
VIC, 1546 posts
16 Dec 2018 7:08PM
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Hi all, by popular request here's some info on my method for converting an old twintip to foilboard. This is the second board I've made for foiling, the first being the 114x46cm beast in this thread - www.seabreeze.com.au/forums/Kitesurfing/Foiling/New-minimalist-home-built-foilboard?page=1

The second board is a 2012 naish momentum, 136x43. Here are the steps:

Cut 12cm off the tail - seal with epoxy.
Drill oversize holes for foil mount and fill with epoxy-microballoon mix (rear holes 12cm from tail).
Sand base and fill channels with epoxy-microballoon mix.
Two tapered and angle offset bits of unidirectional carbon on the base, starting behind the rear mount holes and going as far forward as my front foot.
Two staggered bits of uni-carbon on the deck, again only from the rear mount holes to an estimated front foot position.
Fill coat of epoxy-microballoon mix for the underside, including building up a few mm thick where the mast will sit.
Sand the mast mount area flat.
Drill out mounting holes - 10mm (having marked them earlier so you know where to drill.
Drill satellite 3mm holes for the teeth of the m8 T-nuts to sit in (the oversize original holes are large enough that the satellite holes are still within the filler, so no wood exposed ever.
With a tiny bit of epoxy, set the T-nuts into the holes. Then, being certain that no resin has gotten onto the internal thread of the T-nut, screw a mounting bolt in from the underside, with a few washers on, and tighten moderately. This pulls the T-nut down and seats it firmly on the topside of the board.
As in pics I use countersunk bolts sitting in oversize washers. This lets the angle of the bolt conform to the t-nut, rather than fight it in the case that the t-nut and bottom mounting surface aren't perfectly parallel.
Paint the bottom of the board if you want.
Put some sort of deck grip on the top. (I didn't use a filler on the top laminate as it is all covered by the deckpad.
Ride.

This board handles very similarly to my made from scratch shorter and slightly wider board. Despite much chatter to the contrary they both get going with a similar amount of power and both handle touchdowns very similarly. The only noticeable difference is that on the twintip board, due to rocker between the foil mount and my front foot, my front foot is both slightly higher, and slightly angled back. This is perhaps an advantage when dropping down larger swells, but really I simply get used to whichever board I'm on.

The twintip board took less time and materials to make than the original pawlonia board. The naish worked well because there is no shaping on the topside of this model, so the standing area is all flat.

I'm going to make a smaller (100 x 43cm) pawlonia board with a variation on my original kerfing technique, and ride the twintip board in the meantime, so the original is up for sale if anyone wants a small, light, tough, simple board.

Any questions, hit me up.






Plummet
4673 posts
17 Dec 2018 1:25AM
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TT's aren't made to withstand the point loading and resulting stress riser the plate provides while on the foil.
Long term you will have to provide reinforcement at that area or the board is likely to fail in time.


bigtone667
NSW, 1144 posts
17 Dec 2018 4:34AM
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A wakeskate should work. Plenty of strength.

CJ2478
NSW, 390 posts
17 Dec 2018 8:17AM
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Select to expand quote
Plummet said..
TT's aren't made to withstand the point loading and resulting stress riser the plate provides while on the foil.
Long term you will have to provide reinforcement at that area or the board is likely to fail in time.




Looks like he has used a fair amount of unidirectional carbon on angles in there on each side. I would think it does a pretty good job of distributing the forces transferred from foil baseplate.

djdojo
VIC, 1546 posts
17 Dec 2018 8:23AM
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Yes, between two layers of carbon top and bottom and the epoxy-microballoon pedestal that is a few mm thick at the front of the plate, the load is distributed fine.

Should have added, the carbon is for stiffness as well as strength. Stiffness equals responsiveness for foiling.

djdojo
VIC, 1546 posts
17 Dec 2018 8:31AM
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Select to expand quote
bigtone667 said..
A wakeskate should work. Plenty of strength.


Absolutely. I guess part of this post is to indicate that whatever is cheap and at hand can be used so long as some thought goes into how you get the necessary stiffness and strength. This board had the right amount of pre-built rocker that I wanted to play with, so it got the nod.

There must be plenty of old twintips with pulled footstrap inserts, other damage, or just fallen into disuse and gathering dust in sheds everywhere and ripe for budget-minded foil conversion. I'd say the stiffer the better, so wakestyle boards will be good.

Plummet
4673 posts
17 Dec 2018 2:03PM
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Select to expand quote
CJ2478 said..

Plummet said..
TT's aren't made to withstand the point loading and resulting stress riser the plate provides while on the foil.
Long term you will have to provide reinforcement at that area or the board is likely to fail in time.





Looks like he has used a fair amount of unidirectional carbon on angles in there on each side. I would think it does a pretty good job of distributing the forces transferred from foil baseplate.


Ooops, I missed reading that part. Yes uni carbon layers top and bottom are good. That will fix it up.
Unless it has a foam core or partial foam core. Then there is still a change for shear between core and reinforcement layers.
So.... wood core probably sweet. Foam or foam cap construction potential for failure. But who cares if its a old ****ter board that isnt used anymore.

One thing TT's are bad it is having enough nose scoop so you don't nose dive during high speed touch downs. Using a wake style high rocker board would be best. Or consider cutting and re-glassing more pronounced nose scoop.

AquaPlow
QLD, 829 posts
17 Dec 2018 8:16PM
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Select to expand quote
djdojo said..

Any questions, hit me up.


I really enjoy reading the detail so thank you...
1.. how does the flat washer in the picture of T-washer and bolt get used?
2... I am planning to build 2 boards.. 1 a crude prototype.. and the second fix my preferences in & to last...

Crude model has got to the drawing board..
I have glued a couple of Knauf insulation sheets together and am about to hot wire the shape...
So 1200 length.... and depth ... will be 200 - 250 where the foil plate is and rocker-ed to the nose which will be approx 120-150
(Once I start shaping have a feeling that will end up thinner)....
Too short to resin in some tracks but have planned to have fixed foil plate mount approx rear holes 5-600 mm in.
etc ...
The thick arse end is to give me lee-way to rout out enough space to .....
My "hit me up" question and the unknown is how to ensure the foil plate bolt mounts are strong (so can't pull thru the board...).. I have got some CFibre tubes for compression and had planned to probably grossly over engineer a solution but I have no idea on what is enough...
Thoughts / tips on this aspect would be g8
Thanks
AP

Materials..
2 & 4 oz Glass
a couple of metres of C/F
couple of sheets of thin plywood
Knauf insulation foam = rigid and can walk on but not that strong..
Epoxy resin, chop fibre of glass, Carbon and Q-cell
X-section construct of board resin/glass/CF/ply/foam /ply/CF/glass/resin..
Planned weight 2-2.5 kgs...

CJ2478
NSW, 390 posts
18 Dec 2018 7:44AM
Thumbs Up

Select to expand quote
AquaPlow said..

djdojo said..

Any questions, hit me up.



I really enjoy reading the detail so thank you...
1.. how does the flat washer in the picture of T-washer and bolt get used?
2... I am planning to build 2 boards.. 1 a crude prototype.. and the second fix my preferences in & to last...

Crude model has got to the drawing board..
I have glued a couple of Knauf insulation sheets together and am about to hot wire the shape...
So 1200 length.... and depth ... will be 200 - 250 where the foil plate is and rocker-ed to the nose which will be approx 120-150
(Once I start shaping have a feeling that will end up thinner)....
Too short to resin in some tracks but have planned to have fixed foil plate mount approx rear holes 5-600 mm in.
etc ...
The thick arse end is to give me lee-way to rout out enough space to .....
My "hit me up" question and the unknown is how to ensure the foil plate bolt mounts are strong (so can't pull thru the board...).. I have got some CFibre tubes for compression and had planned to probably grossly over engineer a solution but I have no idea on what is enough...
Thoughts / tips on this aspect would be g8
Thanks
AP

Materials..
2 & 4 oz Glass
a couple of metres of C/F
couple of sheets of thin plywood
Knauf insulation foam = rigid and can walk on but not that strong..
Epoxy resin, chop fibre of glass, Carbon and Q-cell
X-section construct of board resin/glass/CF/ply/foam /ply/CF/glass/resin..
Planned weight 2-2.5 kgs...


Hi mate

Not sure if you habe the foam already but an easy way to make a decent board to foil on is grab a "paipo blank" from these guys www.paulowniatimber.com.au/surfboards.php . The paipo blank is 1200mm x 460mm.

Design shape - i use aku shaper and then print a full size PDF which you can make a router template from or just trace directly onto your blank.

Where you want the foil to go use a spade bit to drill holes about 30mm in diameter. Fill holes with some sort of mixture of epoxy/chopped glass fibres.

Install footstrap inserts if you want.

Glass board with some strategic carbon around foil attachment point. Remember the top is subject to the most forces, so extra carbon here.

Note that the board is flat. I had some reservations about this but it seems to work just fine for me in decent ocean chop kiting with a surf foil.

Here is a video of me riding said board:

LeighMajor
NSW, 339 posts
18 Dec 2018 8:28AM
Thumbs Up

Hey crew
Have two wakeskates on the TTip section.
Solid Timber Core.
Ideal for foil conversions.

Livit
WA, 467 posts
18 Dec 2018 9:05AM
Thumbs Up

Select to expand quote
AquaPlow said..

djdojo said..

Any questions, hit me up.



I really enjoy reading the detail so thank you...
1.. how does the flat washer in the picture of T-washer and bolt get used?
2... I am planning to build 2 boards.. 1 a crude prototype.. and the second fix my preferences in & to last...

Crude model has got to the drawing board..
I have glued a couple of Knauf insulation sheets together and am about to hot wire the shape...
So 1200 length.... and depth ... will be 200 - 250 where the foil plate is and rocker-ed to the nose which will be approx 120-150
(Once I start shaping have a feeling that will end up thinner)....
Too short to resin in some tracks but have planned to have fixed foil plate mount approx rear holes 5-600 mm in.
etc ...
The thick arse end is to give me lee-way to rout out enough space to .....
My "hit me up" question and the unknown is how to ensure the foil plate bolt mounts are strong (so can't pull thru the board...).. I have got some CFibre tubes for compression and had planned to probably grossly over engineer a solution but I have no idea on what is enough...
Thoughts / tips on this aspect would be g8
Thanks
AP

Materials..
2 & 4 oz Glass
a couple of metres of C/F
couple of sheets of thin plywood
Knauf insulation foam = rigid and can walk on but not that strong..
Epoxy resin, chop fibre of glass, Carbon and Q-cell
X-section construct of board resin/glass/CF/ply/foam /ply/CF/glass/resin..
Planned weight 2-2.5 kgs...


Hey mate, I've made a couple of boards using the knauf insulation foam and had good results. When gluing the 2 sheets together, make sure you don't use resin but rather a foam specific glue like 3 M super 77. The hot wire will go though it easy.My schedule for these boards were:
board 1 - Bottom: 6oz glass-carbon patch over tracks- Corecork 2mm (vac bagged) - 4Oz glass
Deck: 4 oz + 6 oz glass - Corecork 2mm (vac bagged)- 4 Oz glass

Board 2 was the same with additional bi axial carbon parabolic rails.

Both have balsa inserts for the tracks and foot strap plugs.

Weight is around 2.5kg. Both have been ridden extensively for the past 2 years with no sign of structural failure. I am only 65kg but the other board has been extensively used by a friend who is over 100kg and jumps pretty big. He is riding the one without the carbon tape...

Don't be afraid to use tracks on them, the board is not too small.

I have tested tracks directly resined into the foam core (i.e no balsa or PVC foam reinforcement) and I have been riding this board for over a year. Touching wood but no sign of failure so far. I ride strapless but I have hit sand bars countless times... The foam I have used on this one has a slightly higher density than the Knauf though.

Just to be safe rather than sorry, use a PVC block or alternatively, you can route out the area and pour a 2 pack polyurethane foam into it. Go minimum 60kg density and you will be covered.

djdojo
VIC, 1546 posts
18 Dec 2018 12:01PM
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Lot's of good info on a range of construction techniques.

The twintip I used has moderate continuous rocker and the very nose never seems to touch down (except if I've really stuffed up and I'm crashing. Regular touchdowns even in chop, seem to hit the board just under my front foot first and the board has no problems bouncing across the tops of chop without the nose digging in. The carbon ensures this rocker doesn't flatten out under load. I just sanded fairly thoroughly into the top and bottom sheets and wiped down with acetone before laminating and this seems plenty strong enough in terms of the bond. No need to sand back to glass. This board has a wood core, so no compression issues.

As above poster notes, even a dead flat board can work so long as you're not touching down too much.

Foils need to be pretty accurate. But boards, especially strapless, are just a rectangle to stand on and while some may be better than others, you can make pretty much anything work.

Swavek
WA, 334 posts
24 Dec 2018 9:51AM
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Got tracks on 106 cm long board - built with advice from Livit. Used itlast night for the first time - solid as a rock, 2.5 kg.






djdojo
VIC, 1546 posts
24 Dec 2018 1:27PM
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^^^^^ Sweet looking rig! Nice work.

Below is a pic requested on mounting with countersunk head screws and oversized washers (all available easily in 316 stainless on fleabay). As explained earlier, I prefer these to panheads as the countersunk screw head can settle in the washer at a range of angles and therefore always pull pretty true to the t-nut, even if the top and bottom of the board aren't exactly parallel. The bigger diameter washer also spreads the load a bit more.



anderkd
2 posts
5 Dec 2019 10:14AM
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Howdy Mates,
New to foiling, but kiting since the dark ages, figured before my knees are totally knackered, I'd start the learning and building process!

Building questions based on reading djdojo's great writeup. I'm using a board quite similar to the Naish used...an old Best Float 133, shown in the picture below. Unfortunately, I don't know if it's a foam core or wood. In discussion with a board building buddy, he suggested that I not use carbon fiber, as I don't have any experience, and in his opinion, the board will flex (if foam core) and cause the carbon to delaminate and make a mess. As I don't have a vacuum table setup I'd be laying it wet with epoxy & cabosil (his recommendation) and I'd muff it up. I understand that the uni carbon used adds stiffness and improves durability. I'm figuring that since I'm just starting out, I won't be able to notice the stiffness that would lead to better performance. My concern is durability naturally. I'm 6'2" and 200 lbs, and although I've beaten this board to death it's never had a hint of a failure. I understand that the forces are considerably different when used as a foil board, so I guess my question becomes does anyone have any real experience with this sort of setup, without carbon reinforcement, that resulted in a failure, or is it just conjecture?

In what might be a total nutter of an idea (take your potshots here if you like!), I'd considered trimming a phenolic plastic cutting board from the dollar store to a footprint roughly double the size of the mast base and inserting it between the mast base and the bottom of the board. My thought is that I could accomplish more load distribution without the potential downside of my possibly crappy carbon laying job. I'd fair it in for hydrodynamic purposes, and it might look goofy as hell, but who cares? Thoughts?

My other question involves the drilling of the oversize holes, which are filled with epoxy & micro balloons. If I'm understanding correctly, the oversize hole would be big enough that the m8 t-nuts would bite into the epoxy mix, and not the board topskin? Or are the holes only slightly oversized, and filled with epoxy mix, then drilled to 10mm, mostly for the purpose of keeping water out of the core? On this thread, AquaPlow suggested using carbon fiber tubes, which I had also considered in lieu of oversized holes, to increase wear resistance of the m8 mounting screws against the exposed foam or wood core. Thoughts from the group on this possibility?

Thanks for your patience in reading through this newbie screed....



djdojo
VIC, 1546 posts
5 Dec 2019 8:45PM
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I don't have time to respond to all the questions in detail now but there are many weak links in your plan. Hold off for a few days and I or someone else will write something constructive. Short answer is you will need either glass or carbon reinforcing both top and bottom of that board. You'll know what the core is when you drill your initial oversize holes (read the steps above) to be filled with something crushproof and waterproof.

freotilo
WA, 18 posts
8 Dec 2019 2:18AM
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im not a very handy person so take my experience with a grain of salt here..

I converted two old twintipps the last two seasons , one was an old cabrinha with foam core and one a slingshot misfit with wood core , both more than 10 years old , I weigh around 80kg and foil most days on a big surf wing riding ocean swell with some minor strapless jump attempts

all I can tell u is I only noticed the flex of the foam board on pictures and after a season of heavy use I only sold it to make a package and the current one seems to hold up pretty well too, so all I'm saying is if th board in question wasn't the biggest investment theres still a good chance it will hold up and while I cut down the last one to a pocket board I will leave the current one as stock to have a twin tip travel option when taking the foil off .

djdojo
VIC, 1546 posts
8 Dec 2019 2:32PM
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Okay, have had time to reread Anderkd's plan.

First up, a 133 twintip will be too small for your first board at 200lbs, unless you're willing to suffer unnecessarily those first several hours. The second hand market is now flooded with good enough boards, cheap as chips, with more surface area to help you get going. (surface area matters, volume doesn't - I and plenty of others learned on shinnsters and brm paipos with minor reinforcing)

Second, a foam core is not a deal breaker in the twinnie, provided you have large (25mm diameter) oversize holes filled with resin-qcell mix. These will resist the crushing load from the t-nut.

Third, a basic hand layup of glass or carbon is really easy. Do a small practise run or two wetting out some carbon on a piece of scrap wood. Get a feel for squeegee and/or roller technique for spreading the resin and working it into the fibres. Youtube is your friend here.

Fourth, if your board breaks just in front of the mount due to lack of reinforcing and your foil is negatively bouyant (it sinks) then it's unlikely that the rear 20cm of your board will float the foil and you could lose it.

Fifth, the choppingboard is not a bad way of avoiding point loading but won't add enough strength or stiffness on its own, though it will add a lot of drag during touchdowns.

Lastly, stiffness matters a lot when you're learning - probably more than when you're competent as you need to learn to feel the foil via the board. Floppy won't work.

Good luck, and enjoy those youtube laminating and load calculation videos.

anderkd
2 posts
17 Dec 2019 3:07AM
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Hey djdojo,
Thanks for the response, it definitely got me thinking!

So, I understand that I'm likely making my learning curve longer by not going with a larger footprint board, but I'm hoping to balance that out by using a 24" mast and a Slingshot space skate for slow, early planing. However, I'm going to look at the classifieds for a board I might buy, rather than creating a project board but....
I've gotten a crazyfly TT wood core, carbon reinforced, which would resolve the durability and stiffness issues, I should think. Think I could also avoid my whack cutting board hack. Lastly, I could likely just sink the t-nuts into the board without the need for oversize holes and epoxy/micro balloons.

The board was gifted to me as it's broken just outside one of the footstrap mounts, so if I go that route, I might just get to learn how to apply that carbon fabric as discussed. I've youtubed, and agree it's surely something I can accomplish without making a mess of it.

I'll document my build, if I do it, on here, which has been so helpful. Thanks to everyone who contributed here.



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"Twintip to Pocket Board Conversion" started by djdojo