Thanks for the info. Currently, I have a SB carbon race foil which I shim with a "Goyard-like" shim at the front bolt. It stays put and doesn't move, even with racing size equipment (9-10 m2 sails, 900-1000 wings). I follow the procedure where I tighten the front bolt first, push the foil with the front wing towards the board, tighten more, and then alternate 2-3 times with the rear bolt/rear wing, etc.

The new setup will have a JP race board with a factory foilbox, which has a flat "ceiling" and a custom carbon foil that also has a square mast. So everything is parallel, in theory, and I should be able to achieve a tight-contact fit with a proper shim.

Providing that with a shim and proper foil installation the mast doesn't move during foiling, and the front screw stays tight, this should be fine, correct? Even if there's not a 100 % front and back rounded taper contact, the loads are distributed to the foilbox "ceiling", which is by default reinforced.

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FormuIa said..
Thanks for the info. Currently, I have a SB carbon race foil which I shim with a "Goyard-like" shim at the front bolt. It stays put and doesn't move, even with racing size equipment (9-10 m2 sails, 900-1000 wings). I follow the procedure where I tighten the front bolt first, push the foil with the front wing towards the board, tighten more, and then alternate 2-3 times with the rear bolt/rear wing, etc.

The new setup will have a JP race board with a factory foilbox, which has a flat "ceiling" and a custom carbon foil that also has a square mast. So everything is parallel, in theory, and I should be able to achieve a tight-contact fit with a proper shim.

Providing that with a shim and proper foil installation the mast doesn't move during foiling, and the front screw stays tight, this should be fine, correct? Even if there's not a 100 % front and back rounded taper contact, the loads are distributed to the foilbox "ceiling", which is by default reinforced.

Sounds like you know more about this than most people. Nothing you've written seems out of line with how the pros are advising people and you have gear designed to be used this way. Sounds like a nice set up! If you were using a ten or fifteen yr old board than this would be a different conversation.

Thank you :) Indeed I've informed myself extensively in discussions with others, manufacturers, and on the FB/forum discussions before trying.

Also, in my experience, older boards aren't necessarily a problem if the fit is tight like @segler mentioned. I've sailed without any issues for two seasons on old Cobra formula board and NP race carbon foil with just a proper deep tuttle fit.

With other foils I had to replace the DT fin box to a reinforced foilbox, because the mast kept rotating in the DT fin box. And if the mast rotates, eventually something breaks: either the box (front or rear) or the deck if you shim it on a non-foil box.

So long term, in my experience, it's better-safer to use a foilbox and to ensure such a tight fit that nothing moves (but there are corner cases obviously). That applies also to IQ board and IQ masts, I've seen the foilbox break due to mast moving during sailing.

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FormuIa said..
Thank you :) Indeed I've informed myself extensively in discussions with others, manufacturers, and on the FB/forum discussions before trying.

Also, in my experience, older boards aren't necessarily a problem if the fit is tight like @segler mentioned. I've sailed without any issues for two seasons on old Cobra formula board and NP race carbon foil with just a proper deep tuttle fit.

Indeed, many of us started and continue to foil on traditional DT boxes where the foil is fitted according to the original design concept. What some find controversial is the newer method of foilbox fitment and allowing some small change of angle through the use of shims.

Slightly off-topic, if you care to share your experience with a custom foil, that would be interesting.

Here is my point repeated again after seglers distracting posts, just being honest segler!

With my AFS W95 foil (angled DT mast head with a flange) and Goya Bolt foilbox (squared off/parallel top) the foil mast head did "not" touch the top of the squared off foilbox. The gap between the front/back top of the AFS DT mast head and the squared off foilbox allowed the mast head (with flange tight against board bottom!) to move slightly resulting in a loose foilbox rear screw after every session. By putting a shim in between the angled DT mast head of the foil and squared top of foilbox, the DT mast head with shim now mates with the top of the foilbox locking the mast head in place AND that prevents movement of the foil AND as a result the foilbox rear screw is no longer loose after a session!

Of course the shim has to be made so that the foil mast head seats in the DT box front/back tapers while mating with the top of the foilbox, or maybe not segler, since the mast head flange is no longer touching the board bottom, so technically the DT mast head is not fully seated with the shim!, but of course there is no movement in mast head when foilbox screws are tight. Same applies with the Phantom foil mast head shims, because by definition the foil mast head will not be fully seated in the foilbox front/back tapers with a high angle shim. Phantom makes facing foils and for some reason I trust what they are doing with the shims versus someone who is not making foils!

Mast head shims for a foil with DT head work great with a Goya Bolt foilbox, here is mine again, after some confusing posts!

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Paducah said..
What some find controversial is the newer method of foilbox fitment and allowing some small change of angle through the use of shims.

Precisely this is the reason I wanted to check with others if shimming can have any detrimental effects on the board (foilbox) structural integrity. Manufacturers do recommend it, but they're also the ones that keep pushing subpar design or engineering solutions, so I take those recommendations with a grain of salt :)

So far I've been using the 1.5 degree mast rake, which is what SB and Remi Villa recommend. But I've seen reports of people shimming for more angle, eg. closer to 2-2.5 degrees on SB IQ foils. Any thoughts on that? Phantom and some others recommend 2.5-3 degrees minimum...

Re: custom foil, I'll need to sail with it first to see how's it behaving compared to the stock SB setup. But then again, as a recreational surfer with an average skill level and no competing ambitions, I doubt I will notice all of the details that a better rider would recognize and utilize.

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FormuIa said..

Paducah said..
What some find controversial is the newer method of foilbox fitment and allowing some small change of angle through the use of shims.

Precisely this is the reason I wanted to check with others if shimming can have any detrimental effects on the board (foilbox) structural integrity. Manufacturers do recommend it, but they're also the ones that keep pushing subpar design or engineering solutions, so I take those recommendations with a grain of salt :)

So far I've been using the 1.5 degree mast rake, which is what SB and Remi Villa recommend. But I've seen reports of people shimming for more angle, eg. closer to 2-2.5 degrees on SB IQ foils. Any thoughts on that? Phantom and some others recommend 2.5-3 degrees minimum...

Re: custom foil, I'll need to sail with it first to see how's it behaving compared to the stock SB setup. But then again, as a recreational surfer with an average skill level and no competing ambitions, I doubt I will notice all of the details that a better rider would recognize and utilize.

The only controversy is from those that have not use shims in a foilbox, or have used shims in non-foilboxes!

Formula, I think you got it. Yes, the industry has evolved a lot in the past 4 years.

I personally never depend on the inside roof because I always use brand-x board with brand-y foil. It's rounded tapers or nothing. Yesterday I was out with a DT no-flange carbon SAB mounted to a Fanatic Stingray 140 DT box. Rounded tapers, baby. Nothing moves, and it will last forever. Whatever the rake angle is, that's what I got. I don't try to (or even need to) change it. The Stingray (and my Exocet FF132) has an inside roof, but I make sure nothing touches it. It's all rounded tapers in my book.

Sandman, your AFS picture above shows a flanged top. How do you ensure inside roof contact when the flange contact to the bottom of the board is tight? One or the other will be loose. Also, the flange will determine the rake angle unless you leave a gap somewhere under the flange.

I proselytize this because I don't like to see broken boxes or boards. Good luck out there. Regardless of how you mount, make sure nothing moves.

segler
Retired Boeing scientist who knows a few things about carbon fiber stressed structure

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segler said..
Sandman, your AFS picture above shows a flanged top. How do you ensure inside roof contact when the flange contact to the bottom of the board is tight? One or the other will be loose. Also, the flange will determine the rake angle unless you leave a gap somewhere under the flange.

Segler, with the shim in place the foil mast head flange does not touch the board bottom, so top of mast head is contacting the inside top of the foilbox via the shim, like it was designed to!

The screws tell the story, no shim = loose rear screw after session, with shim = no loose screws after session, listen to your screws, they are telling you something important!

OK, makes sense. One or other will be loose. However, it defeats the whole purpose of the flange.

The flange spreads the load more onto the bottom of the DT box and bottom skin. This is a good thing. The flange also sets the rake angle.

Is your Goya Bolt "foil ready"? In your pictures in other threads, I don't see any markings to that effect. Prior to 2020 or thereabouts, I believe the Goya Bolt is not a foilboard, or "foil ready" board. That means the DT box is not actually designed for foiling. It lacks the necessary reinforcement to carry fore and aft foiling loads. You have a higher risk of box failure than with a foilboard. The mitigation for this is the flange, which gets some of load back outside to the bottom skin. This is exactly why, all the way back to 2016 when there were no foilboards, Slingshot and LP (and others) included flanges in their tuttle fittings.

I hear this advice all the time. If it is a DT foilboard, you can mount any DT foil to it, but make sure the top is not too tall on the inside (or match brands and tighten to the inside roof). If it is not a foilboard, use a flanged DT foil.

Also, about the screws. The lifting wing is forward of the DT box. Thus, lifting forces tend to rock the foil forward in the box. It is always the front screw that gets loose. The back screw is under high tension all the time. Assuming you have mounted everything tight to start with.

In 5 years of foiling, I have never had a back screw come loose, even before I learned from Sailworks how to mount the foil into the DT box. Before I learned that, I had loose front screws all the time. So did everybody else. Back screws were never loose. So now with the ole wrench-back-tighten-wrech-forward-tigthen-wrench-back-tighter-wrench-forward-tighten... for 4 or 5 repetitions to get a tight fit of both front and back rounded tapers, both screws are just as tight after 20 miles as they were at the beginning.

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segler said..
OK, makes sense. One or other will be loose. However, it defeats the whole purpose of the flange.

The flange spreads the load more onto the bottom of the DT box and bottom skin. This is a good thing. The flange also sets the rake angle.

Is your Goya Bolt "foil ready"? In your pictures in other threads, I don't see any markings to that effect. Prior to 2020 or thereabouts, I believe the Goya Bolt is not a foilboard, or "foil ready" board. That means the DT box is not actually designed for foiling. It lacks the necessary reinforcement to carry fore and aft foiling loads. You have a higher risk of box failure than with a foilboard. The mitigation for this is the flange, which gets some of load back outside to the bottom skin. This is exactly why, all the way back to 2016 when there were no foilboards, Slingshot and LP (and others) included flanges in their tuttle fittings.

I hear this advice all the time. If it is a DT foilboard, you can mount any DT foil to it, but make sure the top is not too tall on the inside (or match brands and tighten to the inside roof). If it is not a foilboard, use a flanged DT foil.

Also, about the screws. The lifting wing is forward of the DT box. Thus, lifting forces tend to rock the foil forward in the box. It is always the front screw that gets loose. The back screw is under high tension all the time. Assuming you have mounted everything tight to start with.

In 5 years of foiling, I have never had a back screw come loose, even before I learned from Sailworks how to mount the foil into the DT box. Before I learned that, I had loose front screws all the time. So did everybody else. Back screws were never loose. So now with the ole wrench-back-tighten-wrech-forward-tigthen-wrench-back-tighter-wrench-forward-tighten... for 4 or 5 repetitions to get a tight fit of both front and back rounded tapers, both screws are just as tight after 20 miles as they were at the beginning.

2019 Goya Bolt 135 has a foil box and is marked as "Foil Ready" on the board bottom.

The AFS mast head flange spreads out the load, yes, and that is important on a non-foil box, and yes the flange also sets the foil rake angle and was likely designed for ADH boards (under the same company as AFS from what I can tell, both are sold on the same AFS website).

As for rear screw loosening on my kit without a shim, that is what it does, probably because the stabilizer is pushing foil upward and that means rear screw is getting stressed more than front screw as the front wing also lifts upward (in front of mast/mast head) and tries to pivot mast head in the box pulling on the rear screw while compressing on front screw. And when up on the foil, front foot pressure will also pull on rear screw of foil.

My AFS foil mast head slips into the foil box snuggly, but with not much effort since the whole weight of the foil is pressing down on the mast head. When it was new, then it took work to get in, but I coated foil mast head with a light coat of silicone grease for a while because it immediately slipped in easily with the silicone grease. After a while did not need silicone to get it in (forgot one time and then realized did not need it anymore), but mast head is still tight in foil box.

OK thanks. Your Bolt is foil ready.

The 2nd paragraph conflicts with itself. You wrote "probably because the stabilizer is pushing foil upward." No, the stab never pushes upward. It always pushes down while the front wing pushes upward. The rest of paragraph explains why the back screw is always in tension while the front screw gets compressed and can loosen up. So, if the back screw is always in tension, it cannot get loose, unless...

...you didn't seat the foil completely when you assembled it. There is no other explanation. Nothing in flight physics will explain the back screw getting loose since the foil never rotates backward--unless you keep hitting those stingrays and turtles and manatees down there or you keep running aground in the shallow waters there.

Point is, the foil in flight always tries to rotate forward. This puts a lot of tension on the back screw and relieves the tension on the front screw. The few box failures I have seen have always been a split box at the front, or a foil that came up through the board at the front, to the point that the front wing strikes the bottom of the board and the back screw is bent but still holding.

See this video. At the end, beginning at 5:25, you can see how the foil had rotated forward and bent the back screw.

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In his slo-mo section look at it very closely at 5:18. You can see the front screw pop up about 1 cm above the plate.

Also the last frame of the video shows the failed DT box. Screenshot below. It split at the front. The front rounded taper moved upwards and split the inside box rounded taper. Unfortunately this is exactly what can happen with DT boxes not reinforced for foiling used with non-flanged foils.

He had a plate for the top of the board to spread the load. However, most of the load is on the bottom of the board. A flange there would spread the load into the skin of the board. With a flanged foil he likely would not have had this failure.

So, back to the recommendations.

1. If you are using brand-x foil with brand-y board that has a DT box not specifically for foiling or "foil ready," use a foil with a flange. Do not shim inside the box; it will produce point loads. This is what happened in the video

2. If you are using brand-x foil with brand-y board that is for foiling or "foil ready," insert to a tight and non-moving connection of the front and back rounded tapers. Do not shim inside the box. It will produce point loads.

3. If you are matching brands of foil and box, just follow their directions. If they provide inside-the-box shims, go for it.

If he made a full length shim to fit the top of the box I'm betting he'd still be using that box.

Okay, feel like I am wasting time responding to seglers comments, so will not! But to everyone else, be careful with what he says, he has dug himself into a hole and will say anything to get out of it!

Here is what I thought of, when a DT foil mast head (so not a squared off head) is in a DT foil box (squared off inside top) without a shim it is essentially floating because the top of the foil mast head does not touch anything. Jam that foil mast head in as tight as you want, tighten the screws as tight as possible, and it is still floating. As a result the back and forth pressures applied to the mast head by the foil can wiggle it by flexing the box, and that will cause the screws to loosen. But once you use a foil mast head shim, the top of the mast head gets locked in place against the inside top of the DT Foil box and then it can not be wiggled loose by back and forth pressure from the foil, and so the screws stay tight.

And that is what a track mount does for a foil mast head, it locks the top of the foil mast head against the bottom of the board/track mount, and as a result the foil can not wiggle the mast head loose.

The other thing to keep in mind is that the tapers on a DT box by design are always trying to force the mast head out of the box! The only thing stopping that from happening are the two screws. In contrast, with a shim locking the mast head against the inside top of the foil box, the tapers are no longer trying to force the mast head out of the box, because the main connection between the mast head and foil box is the top of the mast head and shim.

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Sandman1221 said..
Okay, feel like I am wasting time responding to seglers comments, so will not! But to everyone else, be careful with what he says, he has dug himself into a hole and will say anything to get out of it!

"I might be stuck in a hole, but at least it has a non-moving connection of the front and back rounded tapers!"
- Diogenesegler, circa 320 BC (before Cobra)

Joking aside, in my experience, on a proper foil box, a shim between the mast and the top of the foil box will work fine, providing you install the mast (foil) with back-and-forth alternate tightening pattern. The bolts stay tight even after multiple hours on the water with race gear (formula board, 9-10 m2 sails, 900-1000 wings).

Before shimming I experienced either or both:
- mast rotation during sailing (most often on first jibe)
- incorrect mast rake angle (haven't measured it, but other foilers commented I'm sailing "nose down")

The challenge is sometimes getting the correct shim, as there are a few combinations:
- DT foilbox with either flat or angled top
- DT foil mast with either flat, angled, or transition from flat (front screw) to top

Therefore my solution was to create and 3D print custom shims for each scenario where there's anything else than a flat-to-flat connection between the mast and the foilbox.

So Sandman, now you have introduced a new variable: box flex.

There is no such thing as box flex, even in the old days with boxes designed for fins. And even now with thicker beefier boxes designed for foiling. The wall thickness and fiber direction structure make the boxes absolutely solid.

I have asked about this with the guys that design and build North Pacific and Roberts boards. No such thing as box flex.

Google the aftermarket DT boxes that people offer for board builders. There is no way those thick sections will flex.

Yes, your point about the two tapers tending to push the DT fitting out of the box is a good one. However, all you have to do is make sure that both screws are tight to start with, so tight that there is zero movement. Put both screws in tension by rocking and tightening repeatedly until the screw does not turn anymore. It will all stay together. Mine do. We all learned this during the formula racing days with our 70 cm fins.

Even with all of this, some DT boxes fail. Certain formula boards were famous for this. See the youtube.

Again, all I'm trying to do is help people prevent failures. If you want to ignore this, go for it.

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segler said..
So Sandman, now you have introduced a new variable: box flex.

There is no such thing as box flex, even in the old days with boxes designed for fins. And even now with thicker beefier boxes designed for foiling. The wall thickness and fiber direction structure make the boxes absolutely solid.

I have asked about this with the guys that design and build North Pacific and Roberts boards. No such thing as box flex.

Google the aftermarket DT boxes that people offer for board builders. There is no way those thick sections will flex.

Yes, your point about the two tapers tending to push the DT fitting out of the box is a good one. However, all you have to do is make sure that both screws are tight to start with, so tight that there is zero movement. Put both screws in tension by rocking and tightening repeatedly until the screw does not turn anymore. It will all stay together. Mine do. We all learned this during the formula racing days with our 70 cm fins.

Even with all of this, some DT boxes fail. Certain formula boards were famous for this. See the youtube.

Again, all I'm trying to do is help people prevent failures. If you want to ignore this, go for it.

Everything flexes, wether you think so or not, everything flexes to some degree under load, it just takes enough load. And the foil box only has to flex the smallest amount combined with the tapers pushing the mast head out, for the mast head to try to pull away from the screws. The foil mast can apply that load because of the leverage the wing has over the mast head, dependent on: 1) the length of the mast; 2) how far forward the wing is on the fuselage from the mast; 3) the size/lift of the wing; 4) the board/foil speed; and 5) amount of sail base and front foot pressure on board.

You described how important it is to rock the foil forwards and tighten the front screw, then rock it backwards and tighten the rear screw, and keep doing that several times. You are flexing the box when you do that. If the box did not flex, you would just drop the mast in and tight both screws 1 time and be done. Now I am assuming the mast head does not compress significantly compared to how much the box flexes.

When I install my foil I do not rock it back and forth because it bottoms out on the shim/inside top of box, while just snug in tapers, I just tighten front screw and then back screw and am done, and the screws stay tight during the session.

I accept that.

However, I see it more as an issue of friction. Formula racers rocked their fins for many years.

Since it is a very tight fit, by design, rocking any DT fitting (foil or fin) is a way to make sure it is fully seated, be it roof or tapers.

If you tighten to where the screws don't turn any more, then go out and foil on it, then come back in to find the screws loose, something was obviously not seated (beginners get this all the time until they figure it out). That is not due to box flex. It has to be due to friction keeping you from tightening enough the first time. Sailworks has always espoused McLube, or any other dry teflon spray, to help with the friction.

Rock it, baby, until the screws don't turn any more. For me 5 cycles does the trick. I come back in after 20 miles, and the screws are just as tight as when I assembled it 20 miles ago.

By your own admission you aren't using race sails or fuselage lengths Segler. You simply can't rock it hard enough to seat the mast to the point where that much force won't make it shift in flight. Hence why every race foil company recommends shims.

Don't you guys get tired of arguing over the same thing?

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Gwarn said..
Don't you guys get tired of arguing over the same thing?

Well it did make me think about it, that was good!, but yeah, now I am tired of it, just wanted to set the record straight for anyone who is interested in using a shim.

Wrong, Grant. ONe of my foils is a Moses Race 105-900 which I mount into a Roberts GT 32 foilboard. The board has a regular DT box without a roof, and the foil is non flanged. So, I rock. I really don't like loose screws, either on the board or in my head.

Grant, see the photo. Even the freeride foil has the front wing far enough in front of the mast to cause a forward rocking force. If you don't tighten the screws enough when you assemble, the front screw will come loose. Every time. I see this all the time with beginners. So, rock it baby until the screws don't turn anymore. This ensures a tight fit of the tapers. In the photo the foil on top is the 105-940 freeride with the 900 mm fuse. The foil underneath is the 900-105 race with the 1100 mm fuse. Note that the race places the front wing much further forward of the mast. This is normal for race foils.

If you guys want to keep arguing about this, I'm game, but I think all the other readers are getting pretty tired of it. You always have the proponent and the naysayers. I know which one I am.

I recently got IQ foil SB 95 cm mast and try to fit into FMX foil race board. IQ foil has a cutting guide line but even after cutting on that line, I could not get the angle correctly. Now, I am using Phantom shims; however, mast head is not fully seating even with the shims as discussed before. It is not possible for me to determine exact angle of the top of the mast in relation to the box so that I could make a perfectly fitting shim. I even considered to make a cast while mast is in the box so that I could use the cast as a guide. My screws are still coming loose after each run. Other foilers in our beach are also having problem to fit in their board, even the SB mast going into SB race foil board.

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SA_AL said..
I recently got IQ foil SB 95 cm mast and try to fit into FMX foil race board. IQ foil has a cutting guide line but even after cutting on that line, I could not get the angle correctly. Now, I am using Phantom shims; however, mast head is not fully seating even with the shims as discussed before. It is not possible for me to determine exact angle of the top of the mast in relation to the box so that I could make a perfectly fitting shim. I even considered to make a cast while mast is in the box so that I could use the cast as a guide. My screws are still coming loose after each run. Other foilers in our beach are also having problem to fit in their board, even the SB mast going into SB race foil board.

It didn't fit without cutting it? Oh no

Mine was tight in the IQFoil board but now fits great.

Also, you guys having the bolts loosening up: are you using tefgel? It helps....

Well all I can say about rocking a carbon mast head back and forth in any box, and tightening the screws and repeatedly rocking and tightening, is please send me a good photo of the inside of your box, because I would not be surprised to see cracks in the box tapers and walls! Carbon masts (sail or foil) certainly can flex, but "I do not think" the tapers and side walls of a DT box (carbon or glass) were designed to flex and the rocking and tightening routine described by some would certainly flex the box and could crack it.

And for those using shims and still getting loose screws, it is not easy to get a mast head to seat in the tapers and snug up against a shim on mixed equipment (foil and board not designed for each other). If mast head does not seat in the tapers the shim is too thick, and if it seats in the tapers but does not snug up against the shim, the shim is too thin.

I lightly treat the mast head screws with WD-40, that is it!, and they do not come loose.