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lwalker said..

oscardog said..

lwalker said..

Just don't buy these 75mm M8s for the tuttle-to-mast bolts. www.mcmaster.com/92290A459/
They are only partially threaded (28mm long) and the threads aren't long enough.

Try this for tuttle to mast bolts www.mcmaster.com/93395A535/
Those are supposed to be fully threaded however 80mm long instead of 75mm originals. Maybe someone else knows if threads in mast finish at equivalence of 75mm screw thread, or keep going. Warning: I have not tried them as yet.

Those are 90 Degree Countersink heads - won't work. I haven't yet been able to find M8 75mm socket head bolts in SS-316 with long enough threads. I suppose I could put some washers in there - 28mm of thread should be enough - but I think I'd have make them.

Eh... I guess the tuttle-mast bolts are much less vulnerable than the mast-fuse bolts given the geometry of the connection.

Sorry, my mistake. McMaster Carr only have fully threaded M8 80 mm standard socket hex head in black oxide steel not in SS.

I have not had a tuttle head to mast bolt failure, but have had fuselage to mast bolt failure.

New AvE video explains why it's so important to keep your bolts torqued down:


?t=1043

Edit: Can't seem to get the link to go to the relevant part. It's at about 17:43.

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oscardog said..
I have not had a tuttle head to mast bolt failure, but have had fuselage to mast bolt failure.

I've had fuselage to mast bolts come loose again in recent sessions. This does seem to be a rather persistent problem that occurs with different masts, etc. It's always the screw closer to the front wing that comes loose. Longer sessions (> 2 hour) seem to be worse.

I'm wondering if the "2 screws from below" design is too blame. Load changes on the front wing have a seesaw effect on the screw load. The load is non-trivial, lifting about 100 kg with some leverage (i84 in C position). Load changes are drastic in a breach, but can also be considerable just foiling in chop, where the height often changes by a foot or more in less than a second.

NP uses three screws instead of two. The additional center screw should reduce the net force changes on the front screw quite a bit.
Starboard uses screws coming through the mast from the side, rather than from the bottom. That setup should be much less prone to loosening. What do other brands do? Do any of them ever have problems with screws coming loose? Any mechanical engineers here who can comment?

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boardsurfr said..

oscardog said..
I have not had a tuttle head to mast bolt failure, but have had fuselage to mast bolt failure.

I've had fuselage to mast bolts come loose again in recent sessions. This does seem to be a rather persistent problem that occurs with different masts, etc. It's always the screw closer to the front wing that comes loose. Longer sessions (> 2 hour) seem to be worse.

I'm wondering if the "2 screws from below" design is too blame. Load changes on the front wing have a seesaw effect on the screw load. The load is non-trivial, lifting about 100 kg with some leverage (i84 in C position). Load changes are drastic in a breach, but can also be considerable just foiling in chop, where the height often changes by a foot or more in less than a second.

NP uses three screws instead of two. The additional center screw should reduce the net force changes on the front screw quite a bit.
Starboard uses screws coming through the mast from the side, rather than from the bottom. That setup should be much less prone to loosening. What do other brands do? Do any of them ever have problems with screws coming loose? Any mechanical engineers here who can comment?

Sorry for your frustrations. Starboard uses a belt and braces approach: two side screws plus three bottoms. My AFS has two bottoms but also two sides. Almost everyone else (e.g. NP) uses a socket connection which reduces the amount of movement in the mast/fuse connection instead of a simple butt joint.

I know you tend towards the scientific method more than most - have you tried a torque wrench to verify you are getting the correct tension on the screws?

lwalker, nice vid. Around 17:00 it got interesting for me. Yeah, the forums recognize youtube links but not the time stamps. Nothing you were doing or at least I haven't figured out the magic sauce either. That stretch is also why in a lot of auto repairs, rebuilds, you don't reuse bolts that are under high amounts of tension.

I find my slingshot mast to fuse bolts are a bit loose(not much) after the first couple sessions when you assembled it then after that they stay tight for the season(6-8 months). I use dielectric grease and teflon tape, fresh water, I check that they're still tight every session and they are as tight as I can go without bending the allen wrench or stripping the bolt head. This is on stamped A4-70 stainless steel bolts the stock ones that slingshot supplies as we all know are trash.

Check out Axis foil mounting system. Very unique and smart!

Went out in very marginal light winds yesterday, SS i84 with A4-70 bolts. Was pumping board and sail a lot to extend the gusts, had not added Teflon recently (like Wyatt suggests). After session, both fuse to mast bolts were very loose, maybe a thread and a half loose.

Am thinking board pumping loosens bolts more than constant wind, also was pumping a lot when had failures on original SS bolts.
What do others think?

Have added 3 layers of Teflon and lanolin to bolts for next time.

Waiting for TS/Hurricane Marco/Laura for some wind in next few days. Hope they don't better the coasts too much.

Its strange this "bolt loosening" phenomena.


The only times i've had bolts loosen is when there has been space left in a wedge spot (like front of the tuttle box, or mast to fuse) if the slingshot has a straight mast to fuse (mast sits on top of the fuse, no insert) i'd be worried about how its loosening up.


It cant be good.

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oscardog said..
Went out in very marginal light winds yesterday, SS i84 with A4-70 bolts. Was pumping board and sail a lot to extend the gusts, had not added Teflon recently (like Wyatt suggests). After session, both fuse to mast bolts were very loose, maybe a thread and a half loose.

Am thinking board pumping loosens bolts more than constant wind, also was pumping a lot when had failures on original SS bolts.
What do others think?

Have added 3 layers of Teflon and lanolin to bolts for next time.

Waiting for TS/Hurricane Marco/Laura for some wind in next few days. Hope they don't better the coasts too much.

Try using Tef-Gel and cranking the bolts as tight as you can with the correct size hex key.
I don't bother with the Teflon tape.

My stainless A4-70s don't loosen at all. I check them every session, pull them apart once a month and reapply the Tef-Gel.
I once left them bolted up for 3 months and they were fine when finally pulled apart - Tef-Gel is good stuff.
It's expensive but don't be stingy when applying it.

I replace the bolts (for insurance) every 3 months, 50-70 sessions.
Don't know anyone who's snapped a stainless bolt - we've been using them for 2 years.
3 dudes bent their bolts fighting the shore-break, but bending is good, nothing gets lost. I doubt any other mast-fuse connection would survive getting rolled up the beach.

My biggest wing is the 76 but we ride mostly in ocean swells or high wind river chop, so I expect the bolts are getting as much of a workout as those who ride in light winds with bigger wings

I had this problem until I used tef gel, it's basically like glue!

Overall the Slingshot mast > fuselage connection is very inferior to most other brands now.

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r0d said..
I had this problem until I used tef gel, it's basically like glue!

Overall the Slingshot mast > fuselage connection is very inferior to most other brands now.

From what I've seen the Slingshot mast/fuselage connection does the job just fine. I'm assuming the locals who have no problems have a half decent feel for when a bolt is properly tightened even if they don't use a torque wrench. Some companies have a socket connection sure but they are so shallow the precision of the fitting would have to be spot on, a tap with a hammer press fit, if it was to relieve the bolts of any stress. The NP alloy joint on my kit is not a press fit, it flops around quite a bit until the bolts are tightened. It's essentially a butt joint. Compare that to your tuttle fin box, much deeper and hence, with similar manufacturing tolerances, very little wobble even without the bolts in.

The Naish mast to fuse connection is far superior even on the early foil models. It isn't a but joint the mast and fuse fit together very snugly.
Many others brands are similar (Moses, Starboard, Axis etc).

Naish components are considerably lighter too. (2018 Naish 90cm mast + plate is nearly a 1kg lighter than the SS 90cm mast and plate!).

Slingshot have some catching up to do.

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r0d said..
I had this problem until I used tef gel, it's basically like glue!

Overall the Slingshot mast > fuselage connection is very inferior to most other brands now.

I m using TefGel for all other screws, and have used it for the mast-fuse screws, too. But I'm removing them after each session, and did not notice any difference. Perhaps the "glue effect" happens when they dry out a bit.

I'm using A4 stainless, and wash everything with water after each session. That includes filling up the fuse-mast connection holes completely (and draining them).

I had noticed before that there are gaps at the ends where the mast sits on the fuse


They are also visible when the fuse is attached and screwed down:


This is just one of two 90 cm masts I've been using. The other one had even more problems with screws coming loose. Overall, I've done 24 sessions on these two masts (more sessions on shorter masts due to tide levels).

I may see this problem more because I'm a bit heavier than others (90 kg / 200 lb) and always use the C position (more leverage of the front wing).

My interpretation is that Slingshot develop the mast-fuse connection for kiting, where the "A" position is normally used. That puts the front wing directly under the mast, so it pushes straight up. They later added the B and C positions for windfoiling, but did not adapt the connection to the different stress levels. In their own testing, they are usually using Slingshort boards with smaller foils - meaning B positions.

I am starting to understand what others have said here - Slingshots can be good for learning, but once you've got the basics, upgrading to a different brand can make sense. I'd switch to Starboard in a heart beat, except none of the local stores carry them, and the one store in the US that has them on their web site has a pretty limited selection, plus issues with not filling orders correctly and stopping to respond to emails when you tell them.

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boardsurfr said..

r0d said..
I had this problem until I used tef gel, it's basically like glue!

Overall the Slingshot mast > fuselage connection is very inferior to most other brands now.

I m using TefGel for all other screws, and have used it for the mast-fuse screws, too. But I'm removing them after each session, and did not notice any difference. Perhaps the "glue effect" happens when they dry out a bit.

I'm using A4 stainless, and wash everything with water after each session. That includes filling up the fuse-mast connection holes completely (and draining them).

I had noticed before that there are gaps at the ends where the mast sits on the fuse


They are also visible when the fuse is attached and screwed down:


This is just one of two 90 cm masts I've been using. The other one had even more problems with screws coming loose. Overall, I've done 24 sessions on these two masts (more sessions on shorter masts due to tide levels).

I may see this problem more because I'm a bit heavier than others (90 kg / 200 lb) and always use the C position (more leverage of the front wing).

My interpretation is that Slingshot develop the mast-fuse connection for kiting, where the "A" position is normally used. That puts the front wing directly under the mast, so it pushes straight up. They later added the B and C positions for windfoiling, but did not adapt the connection to the different stress levels. In their own testing, they are usually using Slingshort boards with smaller foils - meaning B positions.

I am starting to understand what others have said here - Slingshots can be good for learning, but once you've got the basics, upgrading to a different brand can make sense. I'd switch to Starboard in a heart beat, except none of the local stores carry them, and the one store in the US that has them on their web site has a pretty limited selection, plus issues with not filling orders correctly and stopping to respond to emails when you tell them.

What you could try with the mast that has the most issues is to take it to a machinist to flatten both edges. The machinist will remove very little to make it flat. It should be very cheap, especially if you find a retired machinist that makes some parts to keep him busy. regarding starboard distribution in the US, I heard that there is a new distributor or something like that and that might Be the reason for some delays lately, but if you contact a store, they can get you any SB foil, even if they don't have it in their website (I have done that)

Have never really had mast bolts come loose and I just use a marine grease with ptfe which is teflon. In order for me to transport my foil I have to remove the mast every time i am sure it puts a little wear and tear on the threads if that happens just flip the mast yea the logo will be upside down who's looking anyway. Stainless bolts are great they do just bend instead of snap in the shore break if you make a mistake.

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azymuth said


Try using Tef-Gel and cranking the bolts as tight as you can with the correct size hex key.
I don't bother with the Teflon tape.

My stainless A4-70s don't loosen at all. I check them every session, pull them apart once a month and reapply the Tef-Gel.
I once left them bolted up for 3 months and they were fine when finally pulled apart - Tef-Gel is good stuff.
It's expensive but don't be stingy when applying it.

I replace the bolts (for insurance) every 3 months, 50-70 sessions.
Don't know anyone who's snapped a stainless bolt - we've been using them for 2 years.
3 dudes bent their bolts fighting the shore-break, but bending is good, nothing gets lost. I doubt any other mast-fuse connection would survive getting rolled up the beach.

My biggest wing is the 76 but we ride mostly in ocean swells or high wind river chop, so I expect the bolts are getting as much of a workout as those who ride in light winds with bigger wings

little tub of tefgel arrived courtesy of Amazon, and Azymuth advice. With the tefgel, looking forward to being able to do downwind carvers and 360's like Azymuth.

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oscardog said..little tub of tefgel arrived courtesy of Amazon, and Azymuth advice. With the tefgel, looking forward to being able to do downwind carvers and 360's like Azymuth.

Great, Tefgel is good stuff.

Thanks re. downwind carves.
But I can't take credit for 360s - that's Simon.

I'm quite heavy at 130 kg, and I love the infinity 99 which gets me up in the light stuff much like the lighter guys, for about 15 to 20 minutes, then the bolts snap. Ive tried all the suggestions, including tapes, different types of bolts, flipping the mast. same result, Perfect for 10 to 15 minutes then it starts getting unstable in roll, then snap.

As much as I love it I was ready to sell it. So this is my last straw. Im certain the issue is that the mast gets crushed where it meets the fuse, then the bolts start to wiggle and metal fatigue kills them.

So ive cut down a pedestal and now instead of a tiny bit of mast meeting the fuse, there is an extended flat section. The mast is supported and the join wont crush at the fuse.

Im yet to try it out. It needs lots of smoothing and TLC, but who could be bothered if it doesn't work.

of course it will add substantial drag, and i can work on that, but it feel super rigid, and nothing like it did before, so I'm very optimistic.

I will report back.

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Heavy1 said..



I'm quite heavy at 130 kg, and I love the infinity 99 which gets me up in the light stuff much like the lighter guys, for about 15 to 20 minutes, then the bolts snap. Ive tried all the suggestions, including tapes, different types of bolts, flipping the mast. same result, Perfect for 10 to 15 minutes then it starts getting unstable in roll, then snap.

As much as I love it I was ready to sell it. So this is my last straw. Im certain the issue is that the mast gets crushed where it meets the fuse, then the bolts start to wiggle and metal fatigue kills them.

So ive cut down a pedestal and now instead of a tiny bit of mast meeting the fuse, there is an extended flat section. The mast is supported and the join wont crush at the fuse.

Im yet to try it out. It needs lots of smoothing and TLC, but who could be bothered if it doesn't work.

of course it will add substantial drag, and i can work on that, but it feel super rigid, and nothing like it did before, so I'm very optimistic.

I will report back.

I didn't have the problem with the original wing, and the 84, lasts many sessions but still breaks.
I'm also using a formula style board and usually a pretty big sail, like 9.5 commonly. It also seems to be worst cranking upwind.

So I expect I am stressing it far beyond the norm, and I'm sure other solutions work under normal conditions.

Surely your dealer or slingshot should address this for you?

Maybe, but the slingshot foils are the ultimate in crossover foils. The big wing I'm sure is fine in a downwind sup configuration. My complaining would probably only end up with restrictions on weight and use, and I've got to admit i'm pushing the boundaries. I'm sure they never had 99cm winds on formula gear carrying 130 kg in mind.

However it should be easy for them to manufacture a solution bit and make money out of the "upgrade" .
I really think its needed. All this stuff about high tech metals and tapes and solutions to crushed mast ends could be fixed with a more appropriate after market joiner.

Over to you slingshot. I'm sure there is a market for the more robust mast to fuselage joiner. Make it even more the ultimate cross over foil.

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Heavy1 said..



I'm quite heavy at 130 kg, and I love the infinity 99 which gets me up in the light stuff much like the lighter guys, for about 15 to 20 minutes, then the bolts snap. Ive tried all the suggestions, including tapes, different types of bolts, flipping the mast. same result, Perfect for 10 to 15 minutes then it starts getting unstable in roll, then snap.

As much as I love it I was ready to sell it. So this is my last straw. Im certain the issue is that the mast gets crushed where it meets the fuse, then the bolts start to wiggle and metal fatigue kills them.

So ive cut down a pedestal and now instead of a tiny bit of mast meeting the fuse, there is an extended flat section. The mast is supported and the join wont crush at the fuse.

Im yet to try it out. It needs lots of smoothing and TLC, but who could be bothered if it doesn't work.

of course it will add substantial drag, and i can work on that, but it feel super rigid, and nothing like it did before, so I'm very optimistic.

I will report back.

Good work,
thats an improvement to the design,
worth a go,

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Gwarn said..

Where'd that come from? Looks more streamlined under the stabilizer and that flange, if tight, will take most of the bending off mast attachment bolts so that they're only really working in tension...Also, nice anodized color.

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aeroegnr said..

Gwarn said..

Where'd that come from? Looks more streamlined under the stabilizer and that flange, if tight, will take most of the bending off mast attachment bolts so that they're only really working in tension...Also, nice anodized color.

I've been through this whole cracked wing and broken bolt thing last year. I just moved over to the Moses line and have nothing but praise about it.

As for this little gem it showed up at my sailing site during lockdown back in May. The person that was riding it was a engineer type that is a sailor from the original F4 group here in the SF bay. The story was that he was testing the mast stiffness. Why is a F4 guy testing a slingshot proto??? Strangely most of the conversation was about the Canard designs(ZEEKO FOILS)????? Then he caught me snapping pictures of it and that was the end of our conversation he shut down on me. So I just shadowed him out on the playground for the 2 days he was there and he has never been back..

At least in my eyes I would think that SlingShot would be farther along in the design process butt. Remember I'm just a nobody foiler so this is just my speculation This is that foil in action he was sailing hydra on formula style board.

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Heavy1 said..
Maybe, but the slingshot foils are the ultimate in crossover foils. The big wing I'm sure is fine in a downwind sup configuration. My complaining would probably only end up with restrictions on weight and use, and I've got to admit i'm pushing the boundaries. I'm sure they never had 99cm winds on formula gear carrying 130 kg in mind.

However it should be easy for them to manufacture a solution bit and make money out of the "upgrade" .
I really think its needed. All this stuff about high tech metals and tapes and solutions to crushed mast ends could be fixed with a more appropriate after market joiner.

Over to you slingshot. I'm sure there is a market for the more robust mast to fuselage joiner. Make it even more the ultimate cross over foil.

I think slingy could sell tonnes of fuselages with flanges. Most of us, buy a fuselage for each wing and leave it set in B or C depending on the needs of the wing. I rarely (maybe once a year) will move a fuselage from B to C. Its great to have the B and C option when starting out as it is super easy to try different wings, but not needed once you get foil addicted.

FWIW I have more miles windfoiling on slingshot foils than anyone I know, and I have never sheared a mast to fuselage bolt but I am only 75kg. I did pop one pedestal to mast bolt but I see these as wearable items after my physics-mate pointed out how much tension that rear pedestal bolt is under.

Hello Gwarn,

Fuselage look like the original 2018 concept with the opportunity to switch from aluminium to carbon don't know why it didn't go through.
www.windmag.com/media/news/17/3mars/2018-WINDSURF-FOIL-COLLECTION-BOOK-032217.pdf

hope they could find back also the 2018 book and integrate it to the Phantasm system

Moses foils, for all their goodness, have a (in my opinion) questionable bolted assembly of fuse and mast. My Moses Race connection there is held together with only two bolts. After foiling, no matter how much I tighten them, the front bolt is always loose. (The lifting front wing will tend to loosen the front bolt and keep the back bolt in tension.) Even trying various lock washers and compressible washers has not solved this problem. Friends with the 790 have also reported this same problem. I can mitigate this by coming in after the first 20 minutes and tightening that front bolt. I suppose I should just carry the hex tool with me out on the water.

I have not had any troubles with the bolted connected of my Slingshot i76 mast to fuse.

The best fuse to mast connection out there is the one-piece monocoque of the AFS-2 and F4. Problem is, you can't disassemble it. For travel or storage you have to live with a big T. But, boy, is that thing stiff! Later models of AFS went to a bolted connection of fuse and mast.

The second best connection is the FRS from LP. The fuse slides into an enclosed bracket that is part of the bottom of the mast. You only need to hold it in place with one bolt to prevent sliding. Even then you have to use a rubber mallet to tap it into place. This can be easily disassembled. The problem with the LP FRS is that the front wing requires a long threaded rod to remove. Kindof a hassle, but the overall structure of the whole foil is bomb-proof. The later RS model went to a conventional bolted connection of fuse and mast and a bolt-on front wing.

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Heavy1 said..
I'm quite heavy at 130 kg, and I love the infinity 99 which gets me up in the light stuff much like the lighter guys, for about 15 to 20 minutes, then the bolts snap.

If you are using a board with tracks (or can get one to try), one possible solution would be to use the "A" position instead of the B position. The A position aligns the mast and the upward push of the front wing much better, which should reduce the stress on the bolts quite dramatically. I have had problems with bolts getting loose in sessions, but fortunately they never snapped. I'm using 316 stainless steel bolts rather than the original titanium bolts.

I think the Slingshot problems can be understood looking at the history of their foils. The original foils were for kiting, where the A position is used. When they expanded to windsurfing and made boards with tuttle boxes, they had to move the wings more forward, and ended up drilling a couple of holes into the fuse. A pragmatic solution that works ok for many lighter foilers, but is quite limited in the amount of load it can take. Other companies like Starboard or Fanatic that designed the windfoil wings from scratch ended up with designs that are mechanically more sound.

In my eyes there is no one foil product that is 100% perfect they all have pro's and con's. Yes the moses mast to fuse bolts do loosen up and need to be tightened. But since it's a tapered pocket it doesn't twist in different directions which I think caused the bolts to break on the SS mast. For me it's about having a product that I have confidence in. My style of riding requires this as if you have doubts in the back of you head about your gear then you aren't 100% focused on riding which is a must for foiling. So you need to find what fits YOUR needs and not what the world around you is telling you what your riding needs are.


. The Moses foils have help me get to where I'm I just couldn't wait for phantasm go come to market so Moses was it for me just this season I have 128 day in 18 mph+ winds here at treasure island in the SF bay. I'll be the first on to tell you I'm excited to get my hands on the Phantasm the 730 infinity withe the 400 stab. Everything in my program from riding style to equipment is modeled after the things I see in the videos of Tonys SlingShot crew. This is why I started build my smaller boards as I couldn't buy any at this time last year. I'm sure once I get one of the Phantasms I won't be looking back at my moses quiver.I just don't have any insider contacts to get myself fast tracked on to the slingshot Phantasm gear so I have to go with what is available today and that is Moses.

www.seabreeze.com.au/forums/Windsurfing/Foiling/Treasure-Island?page=1#16

This is a day on the inside on the playground at Treasure Island It was about 18-22 mph with lulls 3.8 on a cubby 4'9" board and a Moses 790.

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segler said..

The second best connection is the FRS from LP. The fuse slides into an enclosed bracket that is part of the bottom of the mast. You only need to hold it in place with one bolt to prevent sliding. Even then you have to use a rubber mallet to tap it into place. This can be easily disassembled. The problem with the LP FRS is that the front wing requires a long threaded rod to remove. Kindof a hassle, but the overall structure of the whole foil is bomb-proof. The later RS model went to a conventional bolted connection of fuse and mast and a bolt-on front wing.

Newer LP RS foils don't need a rod. Much better and many wings to choose. Best value IMO.