I just finished a great foiling session will post a video on a different thread.
But after realizing I can see two tiny spots of what looks like foam at the front bottom of my fin box on my beloved sb formula 162 ( SEE PICTURE). This makes me confused because that would mean the fin box is super super thin at Least right there it is. Like 1 millimeter thick.

Any help or advice would be appreciated.
had vasale inside that's why it looks shiny.

How well does an ordinary fin fit in the box? Is there some space? That does look thin back there, I'll admit. Any evidence someone sanded it a bit to get a fin to fit?

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Paducah said..
How well does an ordinary fin fit in the box? Is there some space? That does look thin back there, I'll admit. Any evidence someone sanded it a bit to get a fin to fit?

You may be wright. Actually looking inside the box it does seem like there is a very small space compared to the back of the box. It looks like it tapers out at the half way point in the box only on the front where the chip happend. I also have a feeling the weld on the aluminum foil may have got wedged too had against the lip of the box, which is where it chipped.
I have been suggested that my box cracked or shifted and i should take the whole box out. Seems like a wast for a box that may not be damaged that bad. Can you put fiber glass or carbon cloth around the front lower half of my fin box - has this been done before. Will try the ding stick on it though to seal it.

Yes, you can definitely repair a dinged box with glass, cf etc and epoxy. I wouldn't ding stick it because you are better off putting something structural in that space, imho. Good news is that most of the force inside the box itself is compression as long as the shell is intact. You have a bit of leeway.

I absolutely trashed the back of my box after running a bit shallow. Fixed it by filling it with multiple layers of glass and finally a microspheres in epoxy to get the dimensions right under the advice of the board builder. The repair has held up to lots more foiling sessions. Taping off the repair so you don't get epoxy everywhere is definitely recommended as cleaning up inside the box is a nightmare if you get sloppy.

Maybe one of the esteemed denizens of this forum who are repair gurus can chime in further.

Have you poked it? Looks like the solid fill that is part of the box.

BTW don't lube the box, it is supposed to be an interference fit so the fin (foi) is jammed in there and the taper holds it, not the screws. Lubing it is unduly loading the screws and probably then in turn the deck.

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Mark _australia said..
Have you poked it? Looks like the solid fill that is part of the box.

BTW don't lube the box, it is supposed to be an interference fit so the fin (foi) is jammed in there and the taper holds it, not the screws. Lubing it is unduly loading the screws and probably then in turn the deck.

I have not poked it. Am not a starboard designer or repair guru so... no idea if that is yellow foam throughout the whole board...I'm actually kinda unsure how our fin boxes actually stay in place/are mounted?
The box has not shown any signs of movement. But I would like to stengthen that part of the box where it chipped from the foil, also seal it up from water getting in. The good news is I weighed the board and it is the wright weight.

Have an idea in my head, but tell me if im wrong:
one peice of fiberglass cloth aprox 2" up the front part of the fin box and 2" past the front of the box on the bottom of the board wrapping/ hugging the fin box edge where the chip happend or is this not possible or nice with fiberglass cloth.
Would i need multiple layers without making box too small. I feel there is room in the box for it and would snug the foil up better. Should I use some epoxy to seal that part up first or is the fiberglass sufficient enough to keep water out?

When I did mine, I cut strips of glass just the width of the box and layered them up. If you want to put a putty ("consistency of peanut butter") of glass microspheres/epoxy in first to give it a good bed and fill any voids, that might be helpful. Then afterwards, more of the microsphere putty to get the dimension right. The foam you are seeing is probably the PVC (Divinycell, etc) foam that surrounds the box you see which is much stiffer/stronger than the EPS foam of the main part of the board.

from Starboard site - standard tuttle

Go foil deep tuttle like a lot of aftermarket boxes

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Paducah said..
When I did mine, I cut strips of glass just the width of the box and layered them up. If you want to put a putty ("consistency of peanut butter") of glass microspheres/epoxy in first to give it a good bed and fill any voids, that might be helpful. Then afterwards, more of the microsphere putty to get the dimension right. The foam you are seeing is probably the PVC (Divinycell, etc) foam that surrounds the box you see which is much stiffer/stronger than the EPS foam of the main part of the board.

from Starboard site - standard tuttle

Go foil deep tuttle like a lot of aftermarket boxes

The board lady said "EPS", expanded polystyrene, and "XTR", extruded polystyrene foam. EPS and XTR foams melt with exposure to Styrene" is there any other ingredients that can harm the foam core of my board.

Is this the stuff your talking about?
www.google.com/url?sa=t&source=web&rct=j&url=https://expancel.akzonobel.com/applications/polyester-putties/&ved=2ahUKEwiajaeriZHdAhXQk1kKHT22B18QFjAAegQIARAB&usg=AOvVaw3kSvA9rW32_X0vVWAwGdQD

And

www.google.com/url?sa=t&source=web&rct=j&url=https://www.westsystem.com/the-105-system/epoxy-resins-hardeners/&ved=2ahUKEwjfrKmVjJHdAhXptlkKHcRcB2AQFjABegQIAhAB&usg=AOvVaw3fNAFFsAG7WPwI5t_Ms9WV

www.google.com/url?sa=t&source=web&rct=j&url=https://www.ecopoxy.com/ecopoxy-resin-and-clear-hardener/&ved=2ahUKEwjfrKmVjJHdAhXptlkKHcRcB2AQFjAKegQIAxAB&usg=AOvVaw1dAMQ_LIXWN_r9k-mytoH-

Never polyester on anything likely to touch foam. Epoxy works for 99% of your board repairs (I have used polyester cosmetic putty to fill in almost invisible surface flaws because it dries very fast and sands easily) Yes, it will eat a hole right through your foam. Besides, in my neighborhood, no one has built a glass/polyester windsurfer in a long, long time. West and System Three epoxies are what we use locally. Mind the hardeners, if you are doing a big repair, fast hardener is, well, fast and gets hot. Enough of it will melt your foam. Small amounts are fine.

West 403 or 406, are the fillers you'll need to mix in the epoxy. 403 is easier to sand - 406 makes a more versatile paste. Both are nasty to breath so wear a mask. A bit more here: www.fiberglasssupply.com/Product_Catalog/Fillers/fillers.html

I'm glad you've looked up the Board Lady - take the time to read over her site as she has a ton of info. She's a super nice person as well.

I still say poke it.

Lots of boxes are made with a couple layers of glass over a plug (fin head shape) then a big thick layer of butter coloured filler which is strong but not strong .

Then that whole assembly is inserted into the board.

ie: if you got the inside of your box and sandpapered a bit, you would only have to sand thru 0.5mm and then hit a cream to yellow coloured stuff which is a few mm thick. That is still part of the box. It will not be letting water in, nor compromised much in a structural sense.

So before we talk major surgery, and capping with layers of glass that will be hard for a novice to blend in to the surrounding area - poke it.

Get a 2-3mm dia. nail or similar and poke it hard. If you can't poke that nail right thru it and hit foam, then it requires no attention at all.

If the yellowy area is clearly foam, then talk repair - and it wont involve the complexities of glassing over I reckon.

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Mark _australia said..
I still say poke it.

Lots of boxes are made with a couple layers of glass over a plug (fin head shape) then a big thick layer of butter coloured filler which is strong but not strong .

Then that whole assembly is inserted into the board.

ie: if you got the inside of your box and sandpapered a bit, you would only have to sand thru 0.5mm and then hit a cream to yellow coloured stuff which is a few mm thick. That is still part of the box. It will not be letting water in, nor compromised much in a structural sense.

So before we talk major surgery, and capping with layers of glass that will be hard for a novice to blend in to the surrounding area - poke it.

Get a 2-3mm dia. nail or similar and poke it hard. If you can't poke that nail right thru it and hit foam, then it requires no attention at all.

If the yellowy area is clearly foam, then talk repair - and it wont involve the complexities of glassing over I reckon.

Will poke it and see if it is foam.
Bought this epoxy $12.50 CAD though www.google.com/url?sa=t&source=web&rct=j&url=https://www.pcepoxy.com/products/permanent-repair/pc-11-paste-epoxy/&ved=2ahUKEwjWgsaJzZPdAhUqqlkKHWgGD4UQFjAKegQIARAB&usg=AOvVaw3ChM-ritUaNe_K3YnLpxTw

Has anyone heard of this stuff pc-11or is there better stuff out there to use for this application?

Has anyone tryed a metal or some sort of hard material plate that the fin Screws rest on over top of the fin box for added support or does this do very little?

One of the blokes I sail with cut a 15cm x 10cm section of a kitchen nylon cutting board, rounded off the edges and uses this as a load distributor on his slalom board and NP alloy foil. Used for a whole summer with some wicked crashes and no dramas at all.

It's a bigger issue for boards that use boxes with chimneys as there is less to support the screws. The wider you can disperse the force of the screws, the better.

I've seen people use a few layers of cf to thicken the deck, and thin stainless steel plate. Lots of foil companies sell oversized deck washers and AFS sells this

edit: none of this is to lessen KA43's idea. A lot of the washers sold are really just round versions of the same.

I have made a hard plastic plate to distribute the load while my epoxy repair is curing and yes I poked it and it does seem Mark was right about the "big thick layer of butter coloured filler which is strong but not strong" . Hope this box holds up as I would hate to see another solid 10 knot day go by watching the kites

Is it too problematic to install your foil and bend/twist it?

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Mark _australia said..
I still say poke it.

Lots of boxes are made with a couple layers of glass over a plug (fin head shape) then a big thick layer of butter coloured filler which is strong but not strong .

Then that whole assembly is inserted into the board.

ie: if you got the inside of your box and sandpapered a bit, you would only have to sand thru 0.5mm and then hit a cream to yellow coloured stuff which is a few mm thick. That is still part of the box. It will not be letting water in, nor compromised much in a structural sense.

So before we talk major surgery, and capping with layers of glass that will be hard for a novice to blend in to the surrounding area - poke it.

Get a 2-3mm dia. nail or similar and poke it hard. If you can't poke that nail right thru it and hit foam, then it requires no attention at all.

If the yellowy area is clearly foam, then talk repair - and it wont involve the complexities of glassing over I reckon.

this is the finbox that i recently removed from my old formula board and replaced with a foilbox.

it is like Mark describes ;

Hey Doug, Thinking of doing the same to my Formula
Which Foil box did you use and where dya get it?

How high is the box you got?
my board is 11.5cm thick at the tail and the only foilbox I could find is only 10cm

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ducati said..
Hey Doug, Thinking of doing the same to my Formula
Which Foil box did you use and where dya get it?

How high is the box you got?
my board is 11.5cm thick at the tail and the only foilbox I could find is only 10cm

hey , how's it going ?
the box i bought is a NeilPryde RS:FLIGHT FOIL DEEP TUTTLE BOX , SHQ have them on their website as a special order item. NP images online show them as 100 x 206 x 120 tall so it should be just tall enough to tie into the deck of your board. ( though one site does suggest they are 130 tall , I don't recall how deep mine was before I cut it )

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fjdoug said..

ducati said..
Hey Doug, Thinking of doing the same to my Formula
Which Foil box did you use and where dya get it?

How high is the box you got?
my board is 11.5cm thick at the tail and the only foilbox I could find is only 10cm

hey , how's it going ?
the box i bought is a NeilPryde RS:FLIGHT FOIL DEEP TUTTLE BOX , SHQ have them on their website as a special order item. NP images online show them as 100 x 206 x 120 tall so it should be just tall enough to tie into the deck of your board. ( though one site does suggest they are 130 tall , I don't recall how deep mine was before I cut it )

Thanks for the pics fjdoug.
I may have to do this eventually when my box dies as well. How long an operation does this take. I guess the NeilPryde RS:FLIGHT deep tuddle box would fit pryde foils best.
It seems tuddle shapes differ slightly from one brand to another.

I have read about people making a spacer to fit inside a deep tuddle box to fill the gap between the top of the foil and the top of the box.
Do theses spacers do much or break you box quicker by driving more force through that small area of the deck above the fin box?

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CAN17 said..


I have read about people making a spacer to fit inside a deep tuddle box to fill the gap between the top of the foil and the top of the box.
Do theses spacers do much or break you box quicker by driving more force through that small area of the deck above the fin box?

I've experienced cracks in the tuttle box when not using the spacer.
I've since discussed it a lot with Jean Lou Colmas (creator of starboard) and he agrees you should do everything you can to avoid any movement possibility in the box. Ie fill it with a spacer or q cell epoxy.

I've done it on 2 x fires/ 1 patrik/ 2 starboards, owners never had an issue since.
On my latest board (the fat tiki) it seemed to me that the foil was a tight fit in the box, so I didn't bother checking if there was a gap (I could see marks in the paint at the bottom of the box so I thought it touched everywhere.)
On my third session I started hearing loud cracks, so I came back real slow to the beach, and when removing the bolts I noticed the front one was easy to get out, like undone..)
The foil had just slightly moved upwards and forward in the box.

Measured the gap and it needed 3/4 mm fill at the front. Did just that and tried it: perfecto, no cracks, no movement.

So yes I think the spacer/filling is needed.
I've seen dedicated foil boards (Elix/RRD) top deck crack under pressure, but in my opinion because the foil moved upwards in the box.

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seanhogan said..

CAN17 said..


I have read about people making a spacer to fit inside a deep tuddle box to fill the gap between the top of the foil and the top of the box.
Do theses spacers do much or break you box quicker by driving more force through that small area of the deck above the fin box?

I've experienced cracks in the tuttle box when not using the spacer.
I've since discussed it a lot with Jean Lou Colmas (creator of starboard) and he agrees you should do everything you can to avoid any movement possibility in the box. Ie fill it with a spacer or q cell epoxy.

I've done it on 2 x fires/ 1 patrik/ 2 starboards, owners never had an issue since.
On my latest board (the fat tiki) it seemed to me that the foil was a tight fit in the box, so I didn't bother checking if there was a gap (I could see marks in the paint at the bottom of the box so I thought it touched everywhere.)
On my third session I started hearing loud cracks, so I came back real slow to the beach, and when removing the bolts I noticed the front one was easy to get out, like undone..)
The foil had just slightly moved upwards and forward in the box.

Measured the gap and it needed 3/4 mm fill at the front. Did just that and tried it: perfecto, no cracks, no movement.

So yes I think the spacer/filling is needed.
I've seen dedicated foil boards (Elix/RRD) top deck crack under pressure, but in my opinion because the foil moved upwards in the box.

I have decided to make my own spacer. Found this post www.seabreeze.com.au/forums/Windsurfing/Foiling/Foiling-4?page=2
See pages 2-4.
Why don't foil/windsurfing brands sell theses? It seems like it could save a lot of boxes or does Pryde or naish want your windsurfing board to fail so you buy there foiling boards
Is painting it with epoxy the only thing to save the wood from rot. What about staining it with wood stain.

what foil are you using Can ?
If your beloved sb formula will be solely used for foiling I would rather recommend filling the box over the use of spacer.

My wooden spacer gave way under pressure (not much wood left around the bolt holes...).

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seanhogan said..
what foil are you using Can ?
If your beloved sb formula will be solely used for foiling I would rather recommend filling the box over the use of spacer.

My wooden spacer gave way under pressure (not much wood left around the bolt holes...).

It's a neilpryde rs:one convertible aluminum foil. Without a flang.

worth doing the fill up technique if you're not going to use it as a formula anymore.
I did it on my patrik after the wooden spacer failure and still used the board with deep tuttle fins, just needed to chop off approx a 1/2 cm from the top of the fin.

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seanhogan said..
worth doing the fill up technique if you're not going to use it as a formula anymore.
I did it on my patrik after the wooden spacer failure and still used the board with deep tuttle fins, just needed to chop off approx a 1/2 cm from the top of the fin.

Sorry, what is the fill up technique?

fill the gap above foil head with qcell loaded epoxy; easy job and you're then sure you have a perfect fit.

There's a little prep, but all quite simple.
I smear the foil mast head with grease, fit it in the board, then I insert two straws (the best are from maccas) with the greased bolts in them, tighten the bolts. Once I'm happy with the angle I drill two holes from the top of the deck between the two bolts.
I apply tape to protect the deck.

Then I fill the gap with qcell expoxy from a syringe in the holes. When it comes out from the other hole you're good.
Let it cure overnight, unbolt, remove foil/straws, and voila !

Bonus : when you drop the bolts in the board they just fall neatly in the inserts, thanks to the tunnel/guide made by the straws.

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seanhogan said..
fill the gap above foil head with qcell loaded epoxy; easy job and you're then sure you have a perfect fit.

There's a little prep, but all quite simple.
I smear the foil mast head with grease, fit it in the board, then I insert two straws (the best are from maccas) with the greased bolts in them, tighten the bolts. Once I'm happy with the angle I drill two holes from the top of the deck between the two bolts.
I apply tape to protect the deck.

Then I fill the gap with qcell expoxy from a syringe in the holes. When it comes out from the other hole you're good.
Let it cure overnight, unbolt, remove foil/straws, and voila !

Bonus : when you drop the bolts in the board they just fall neatly in the inserts, thanks to the tunnel/guide made by the straws.

Thank you for that advice seanhogan.
Why wouldn't I be able to use my formula fin with the board anymore. I pritty sure the head of the foil mast is very similar in shape to my formula fin head.

In my case the 48 cm sonntag deep tuttle head would stick out a little..... all depends on the size of the foil head.