My mast does not reach the bottom of my DT box. I feel like I have a very good fit, when the mast bolts are tightened, the whole thing is very solid and stiff. However, I've been unable to prevent my forward mast bolt from loosening during my session. I have replaced my panhead screw with a hex head and I believe I'm getting a good amount of torque on the bolt. The back bolt never loosens off. The only thing I can think of is that the mast is being raked forward during the session, which results in the front bolt losing its tension and therefore thread friction.
I've taken some measurements and I think I can 3D print a spacer/shim that would go under the mast head at the front. I am very unsure of the profile I should give it though. It seems to me that it would be extremely finicky to put in place since the shim will be trapped but maybe it wouldn't be too bad. I can print some this week at work. The angular cut mast head complicates things a bit for the design, picture shows what I mean.

In the meantime, I'm wondering if anyone:
1. has had similar problems with mast bolts loosening
2. has pictures of their shims that could share
3. have any trouble shooting tips.

Re: #3 I was thinking about putting some tape or something on my mast near the board to see if the mast is actually moving while sailing, so that's one thing I can try.

I have a3d printer and made up some shims which sit in the bottom of the box.
Also made them so that I can achive varying tilt on the mastas well.

You can buy the exact shim to fill the void, it generally comes as part of a mast shimming kit.

But the actual problem is when you're putting the mast in, you need to get the mast all the way in. I spend some time bumping the mast back and forth, then tensioning the bolts as i go, till the bolts don't want to give any more. You really want to get the mast head making full contact with box, then with the bolts tensioned nothing can move. The movement comes from the upward/forward pressure the foil puts on the mast head connection (it happens all the time).

as a side note, if you're using the rubber washers that usually come with the kit, stop using them. Because they can further compress and let movement happen. I cut some plastic washers out of a container lid. Not compressable, but at least theres still a layer there thats not straight steel onto board.

This is a very common problem, and when it sinks further in at the front it's messing with mast rake [mast angle] and you don't want that, 100% you need a very accurate spacer to fill the full void. If possible, seek help from others in your local sailing area with experience doing this, we can go around in circles here on the forum but hands on assistance is way better
Happy sailing

Do you install the fuselage and then rock the mast forward, thighten the front bolt, rock back, tighten the back bolt, and repeat this several times? That's the best way to have a very tight fit. Every time you rock the mast with the help of the fuselage you tighten the bolts a little bit.

WillyWind has it exactly right. We need to rock-tighten-rock-tighten etc until the bolts don't turn anymore. That way we have achieved full intimate contact between the foil head and the box at the front and rear rounded tapers.

Loose front bolts were a common thing in 2016 when we were all just getting started and did not know what was causing it. As stated above, the main wing, being forward of the pivot point, will tend to push up really hard on the front of the foil head. With guidance from such people as Sailworks, we all went to the rock-tighten-rock-tighten etc method. I still use it. My front bolts are still tight after a session.

All this stuff about inside shims and roof contact, etc, scares me because that is bad engineering. Changing the rake in a tuttle box is--well--ouch. The box is designed for intimate contact at the front and rear rounded tapers. (It was never designed for inside roof contact.) Anything else introduces point loads, movement, and much higher risk of failures.

If you want to mess around with rake, use a plate mount and shim that.

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segler said..


All this stuff about inside shims and roof contact, etc, scares me because that is bad engineering. Changing the rake in a tuttle box is--well--ouch. The box is designed for intimate contact at the front and rear rounded tapers. (It was never designed for inside roof contact.) Anything else introduces point loads, movement, and much higher risk of failures.

I know we've had this discussion before, and I understand where you're coming from with shimming angle in being a bad thing, and I don't think Shmish actually needs a shim. But as to the actual foil head (no shim) making roof contact in the box, you do realize if it doesn't make roof contact, then the tapers are not making contact either right? Foil mast heads are made to make contact with the WHOLE box, not just the tapers. The board is re-enforced top and bottom to deal with it, because it has to.

To TS:
get/make some of these www.chinook-leucate.com/Recherche.aspx?id_t_famille=1&id_t_sousfamille=157&occazfiltre=new&type=Pi?ces+d?tach?es+Foil&id_t_article_entete=90295&pagecourante=1&NbParPage=26

And don't worry about breaking your box ;
This has been discussed ad infinitum and it's not going to happen unless you weigh 120 Kg and use a 10 m sail in and old tuttle box board .

Oh and also read this about the importance of mast rake : www.windfoilen.nl/en/mast-rake-explained/

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WillyWind said..
Do you install the fuselage and then rock the mast forward, thighten the front bolt, rock back, tighten the back bolt, and repeat this several times? That's the best way to have a very tight fit. Every time you rock the mast with the help of the fuselage you tighten the bolts a little bit.

Maybe I can do a bit better job on this. I usually rock it, but only once. eg tighten the for bolt, rock the mast aft, tighten the aft bolt, re-tighten the for bolt. I could do more cycles of this.

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Bellerophon said..
To TS:
get/make some of these www.chinook-leucate.com/Recherche.aspx?id_t_famille=1&id_t_sousfamille=157&occazfiltre=new&type=Pi?ces+d?tach?es+Foil&id_t_article_entete=90295&pagecourante=1&NbParPage=26

And don't worry about breaking your box ;
This has been discussed ad infinitum and it's not going to happen unless you weigh 120 Kg and use a 10 m sail in and old tuttle box board .

Oh and also read this about the importance of mast rake : www.windfoilen.nl/en/mast-rake-explained/

Thanks, I am going to make some shims like those.

Hey Sub, yes, you're right. Contact on the inside roof if fine if you match both brands and models of board and foil. Made for each other with special reinforcements, etc. When I started foiling in 2016 I came from formula racing. All we had were deep tuttle boxes and deep tuttle foil tops. We had no choice but to fit disparate brands together.

Tuttle's original design says nothing about contact on the inside roof. It is ONLY for the fore and aft rounded tapers. In fact, the design does not specify a height at all. You can make the box as short or as tall as you want, and everybody did, with lots of height variation. Everything from 1 inch regular tuttle to 5 inch super-deep tuttle and everything in between.

I now use SABfoil, AFS, and LP with all different kinds of boards. No inside roof contact or shims for me, don't want it. Whenever I fit a tuttle foil to a new board, if I detect inside roof contact, I shave off the top of the foil fitting until there is no roof contact. Fore and aft rounded tapers only. It all works, and I have never had problems with broken boxes. The rake angle is determined by the box. Yesterday I foiled with SABfoil and Fanatic board.

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segler said..
I now use SABfoil, AFS, and LP with all different kinds of boards. No inside roof contact or shims for me, don't want it. Whenever I fit a tuttle foil to a new board, if I detect inside roof contact, I shave off the top of the foil fitting until there is no roof contact. Fore and aft rounded tapers only. It all works, and I have never had problems with broken boxes. The rake angle is determined by the box. Yesterday I foiled with SABfoil and Fanatic board.

don't do this...

Make shims, tune rake. It's literally what every manufacturer and good foiler recommends.

I had +100 hours of foiling time on a shallow tuttle with ZERO taper engagement, only roof contact, and I weigh +90kg.
I can also show you a formula board with a split box which had 100% taper engagement and no roof contact.

How many of those manufacturers and "good foilers" are actual engineers who understand structures. Probably few to none.

The formula board you are talking about is the famous Starboard model with the defective box structure. They all broke.

Some people are inventing problems, where everything is ok.

Shim Your mast, tighten the screws properly and go foiling!

Broken boxes is not an invented problem. It's a real problem, and it's not ok.

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segler said..
....Tuttle's original design says nothing about contact on the inside roof....

As has been said many, many times, the modern Foilbox only has the side dimensions in common with the classic tuttle and little else. The tuttle dimensions make no reference (that I've seen) to wall thickness, construction (or even roof). What we are discussing here is the foilbox. Not a deep tuttle box. Not the box in my old 2004 Starboard formula board.

There is little comparison in construction with the DTT boxes built and fitted to formula boards 20 years ago with modern foil boxes. There is a whole lot more PVC foam and carbon fiber. Starboard specifically builds their boxes to make roof contact with the foil. They specifically make shims for roof contact. Phantom specifically say to shim their foils in their boards. They are very specific about what angles they feel give the best performance. They send an entire rake shim set with their foils specifically to shim their foils.

Beating the already very dead horse. Below is a pic of a Chinook Deep tuttle box followed by a DTT dimensioned foilbox from Seatex. See if you can spot the differences.

source:chinooksailing.com/collections/board-building-part-accessories/products/race-box


source:seatexboards.com/product/deep-tuttle-foil-box-fin/

How Seatex builds a foilbox

The whole Tuttle Box / Foil Box saga started because we were trying to use windsurfing boards for Foiling.
Foils should have changed & box position should have been ~30cm further forward.
If the mast attached directly above the front wing COE there would no or very little load on the box.
As usual with the windsurfing industry they just keep patching things up & making them stronger & heavier until they stop breaking instead of actually designing! Who's got the balls to change the system??

Mast attached directly above the wing has directional stability issues. Foil boards were moving the box forward for a few years but they are pretty much back where fin boxes were on race boards now.

I agree with us using a box which wasn't designed for vertical load. Fortunately getting roof contact solves most of those issues.

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Grantmac said..
Mast attached directly above the wing has directional stability issues. Foil boards were moving the box forward for a few years but they are pretty much back where fin boxes were on race boards now.

I agree with us using a box which wasn't designed for vertical load. Fortunately getting roof contact solves most of those issues.

It's not so much the vertical load as the 100kg with 30cm of leverage rolling the mast forward in the box.
There's a guy in the US making foils with the mast above the front wing & I don't believe he's had any issues.

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AUS 808 said..
The whole Tuttle Box / Foil Box saga started because we were trying to use windsurfing boards for Foiling.
Foils should have changed & box position should have been ~30cm further forward.
If the mast attached directly above the front wing COE there would no or very little load on the box.
As usual with the windsurfing industry they just keep patching things up & making them stronger & heavier until they stop breaking instead of actually designing! Who's got the balls to change the system??

When foiling started, foil makers did experiment with where to put the box. And it ended up where it is now. There are a variety of reasons for it (including stance, how the board sails prior to leaving the water, etc). This was confirmed on this forum years ago by Chris from F4.

"Hoping everyone is doing well. Just wanted to mention a few things we've learned with ++ fuselages over the last couple years. We did try moving the fin box forward thinking that shortening the distance between the front wing and mast would solve a lot of issues. This just didn't work well. The existing box positions on the race boards with their current volume distribution work better."

www.seabreeze.com.au/forums/Windsurfing/Foiling/Starboard-Fuse-115-vs-115-?page=3#3

AHD on their early foils (like 10-15 years ago) had the mast further forward but now it's in a more conventional position. They've always built both foils and boards. There is nothing keeping most board companies moving the box as they also make their own brand of foils. Starboard, Slingshot, Phantom, Fanatic, NP, Patrik, Horue, etc all could have moved the foil position. They certainly moved mast track and foot strap locations.

Position of the mast is not only about where the wing is, it's about where the lateral resistance of the foil mast is as well. That's an important part of the physics of a windfoil vs wing or kite.

You can do this with any dual purpose board right now. Just use a wing fuse and the wing position for the foil. There have been some people on this forum who've done that. It works for some for a particular kind of riding (upright freeride) but it's not seeing wider adaption for good reasons. Maybe in the future there will be a change in rig and board design that permits it - who knows - but it's not for a lack of people and manufacturers experimenting.

When the box and foil top are purpose-built--and matched--this is all fine. Go for it and shim away. But watch out. Even if you are using a box that is designed and stressed for inside roof contact, you will still get point loads on the fore and aft rounded tapers if you change the rake. If all the load is carried by the roof, then the point loads are probably small enough not to be a problem. Recent racing history has shown this to be the case.

My gear is mixed, as is the gear of most other recreational windfoilers. That means deep tuttle without inside roof contact. You don't want to be shimming mixed gear.

The only rake shimming I will ever do is with a plate mount. No point loads that way.

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segler said..
When the box and foil top are purpose-built--and matched--this is all fine. Go for it and shim away. But watch out. Even if you are using a box that is designed and stressed for inside roof contact, you will still get point loads on the fore and aft rounded tapers if you change the rake. If all the load is carried by the roof, then the point loads are probably small enough not to be a problem. Recent racing history has shown this to be the case.

My gear is mixed, as is the gear of most other recreational windfoilers. That means deep tuttle without inside roof contact. You don't want to be shimming mixed gear.

The only rake shimming I will ever do is with a plate mount. No point loads that way.

I don't think the issue is about mixed gear: if you have a board with a foilbox that was designed to support the loads on the roof of the box, you can shim the mast. Freeriders might no need it, but freeracers and racers definitely do.

The reason I say "mixed" is this: is the foilbox for Starboard exactly the same as the foilbox for Fanatic or the foilbox from other brands?

I doubt they are the same. The only thing that is an absolute standard is the tuttle design.

Starboard wants you to use Starboard foils with Starboard boards. Fanatic wants you to use Fanatic foils with Fanatic boards. Etc.

When you get good roof contact it doesn't matter if the tapers fit perfectly. So if anything a mix and match setup is even more dependent on getting the shim correct.

Of course almost all brands are made by Cobra so all the boxes are the same. The exception would be small boutique builders who should definitely know enough to have their boxes able to be shimmed.

The dt boxes on my Roberts GT32 and North Pacific 135 foilboard are far too tall on the inside to be roof-shimmed with my Sabfoil and AFS foils. The rake is already perfect. No need to shim.

So, if you're going to shim the inside roof, be sure to match brands so you can be sure they fit together AND were designed and stressed for it. Or go with plate mount.