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boardsurfr said..

gorgesailor said..
I believe 316 is more corrosion resistant but marginally weaker than 18-8.

Bolt Depot says the opposite, that 316 is stronger. ASM data sheets seem to confirm that - they give 580 MPa as the tensile strength for 316, and 505 MPa for 304 (from asm.matweb.com/search/SpecificMaterial.asp?bassnum=MQ316A and asm.matweb.com/search/SpecificMaterial.asp?bassnum=MQ304A).

It depends on the type of strain I guess - tensile wise it appears you are right but 304 has 70% elongation at break...& then there is 303 which has tensile strength of 620 mpa... so which 18-8 is it? ... hard to say. My references say that it will depend on how the part is made. Some will use 304 stainless but many will use 302 for easier cold forging or 303 for easier machining...

304 is veritable rubber when you watch it on a tensile test machine. I would prefer 316.

One out of one clinical tests show that:




Foil with 84 cm wing and 71 cm mast does not float




Fuselage with 84 cm wing and 48 cm stabiliser will float




Fuselage with 84cm wing and 42 cm stabiliser will also float




Fuselage with 76 cm wing and 42 cm stabiliser will sink

so if the bolts snap, make sure you are using the 84 cm wing

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MrA said..
One out of one clinical tests show that:
Fuselage with 76 cm wing and 42 cm stabiliser will sink

Is that a saltwater pool?

Had a three hour foil session on the 76 today (sharing the foil with my wife), and discovered afterwards that both screws connecting the mast to the fuselage had loosened a bit. There was a ~ 2mm gap on one side between mast and fuselage. I can see how that could lead to bolts snapping. I think I'll skip the teflon tape next time for the mast screws.

I've found if you coat the bolts with a generous amount of TefGel, in addition to providing corrosion protection, it helps keep the bolts tight.

I disassemble the foil and reapply the TefGel about once a month.

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azymuth said..
I've found if you coat the bolts with a generous amount of TefGel, in addition to providing corrosion protection, it helps keep the bolts tight.

I disassemble the foil and reapply the TefGel about once a month.

Thanks. I did not know there is such a thing as TefGel. Seems similar stuff is available with other names.

The teflon tape tends to punch up in unpredictable ways, which must let salt water in. I've been disassembling the foil completely about once a week since it's new and I wanted to get a feel for what's going on. The stuff I wiped off the screws was usually black, which I take as a sign of corrosion. Removing the teflon bits is a PITA, not something I want to do all the time. I'll try the TefGel stuff and see how that works instead.

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boardsurfr said..

azymuth said..
I've found if you coat the bolts with a generous amount of TefGel, in addition to providing corrosion protection, it helps keep the bolts tight.

I disassemble the foil and reapply the TefGel about once a month.

Thanks. I did not know there is such a thing as TefGel. Seems similar stuff is available with other names.

The teflon tape tends to punch up in unpredictable ways, which must let salt water in. I've been disassembling the foil completely about once a week since it's new and I wanted to get a feel for what's going on. The stuff I wiped off the screws was usually black, which I take as a sign of corrosion. Removing the teflon bits is a PITA, not something I want to do all the time. I'll try the TefGel stuff and see how that works instead.

You can often find Tefgel in the US cheaper on ebay than Amazon. Comes in different sized tubes so beware deceptive pricing.

It's also pretty sticky, unlike grease, so it tends to stay where it's put. Neat stuff.

^^^
Good to apply TefGel correctly if you're only disassembling the foil monthly;

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azymuth said..

snides8 said..
I used my new slingshot foil for the first time on the weekend.
i must admit I was sceptical of the mast fuse connection when I first put it together.
i think there will be lots of broken bolts with the use of large foils and long masts especially and heavier riders.
It's a good set up for Metal fatigue in the bolts
in my opinion.

I snapped my titanium bolts (fuse/mast) a year ago, I suspect that I hadn't tightened them sufficiently, perhaps they worked a little loose making them easier to snap.
I reported it to Slingshot USA, they responded saying they would pass the info on to Wyatt (Slingshot Brand Mgr). All good

I replaced the bolts with stamped stainless steel A4 70 - cost only a few bucks each.
I've foiled 150+ sessions, 4500 km on these bolts often in big swells and winds, with all wing sizes including 84cm.
Might be time to renew them (preventive maintenance) - does stainless weaken appreciably with that amount of use?

I reckon you could over-engineer anything so it never breaks - but then you're probably dragging extra size/weight around and perhaps incurring an additional cost.
I'm happy to replace a couple of bolts every year if need be, and enjoy the carve of the awesome Slingshot foils

I just ordered A4- 70 bolts. Glad you have had success with these bolts.

@segler- I realize they are 314 grade stainless not 316. From what I read on the web 314 has a higher tinsel and yield strength then 316. Is this true?

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azymuth said..
^^^
Good to apply TefGel correctly if you're only disassembling the foil monthly;

Directions unclear. Not sure if I'm using warshas or not.


Seriously, though, while I was good about making sure the bevel on my screws was getting tefgel'ed, it is a good reminder.

when a foyle can swim it's great. But when the foil drowns you cannot prove that it was done badly. How did the FRPGEAR badly embedded on the foyle and at the first ride the wing was torn off and the wing sank.

Had a bolt fail on Slingshot fuselage today. Tried the 35.4" mast for first time, (still learning). The mast bolts were tightened only a few hours before the failure. On Infinity 84 wing, maybe a few small breaches, front bolt sheared.

Windsurfed back using the mast as a fin, with tail wing hooked under the back foot straps, and main wing sitting on the water.

Appreciate all the metallurgical discussion in this post, will try to get some 316SS bolts.


The other half of the sheared bolt is still in the thread. Thanks for the advice on how to remove, will get a left hand drill bit to get out.

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oscardog said..
Had a bolt fail on Slingshot fuselage today. Tried the 35.4" mast for first time, (still learning). The mast bolts were tightened only a few hours before the failure. On Infinity 84 wing, maybe a few small breaches, front bolt sheared.

Windsurfed back using the mast as a fin, with tail wing hooked under the back foot straps, and main wing sitting on the water.

Appreciate all the metallurgical discussion in this post, will try to get some 316SS bolts.


The other half of the sheared bolt is still in the thread. Thanks for the advice on how to remove, will get a left hand drill bit to get out.

I had success on a different bolt that lost its head by using a smaller regular drill bit and drilling into the remaining bolt halfway, then reversing the drill and the bolt backed out nicely

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thedoor said..

I had success on a different bolt that lost its head by using a smaller regular drill bit and drilling into the remaining bolt halfway, then reversing the drill and the bolt backed out nicely

I tried that when it happened on mine but I was using the lanolin grease instead of tefgel and it merely pushed the bolt further in. A left hand thread drill bit worked just fine.

North beach Windsurfing immediately sent a new mast and titanium bolts under warranty.

Got some 316SS bolts from McMaster-Carr, am using those.

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MrA said..
One out of one clinical tests show that:



Foil with 84 cm wing and 71 cm mast does not float

Fuselage with 84 cm wing and 48 cm stabiliser will float

Fuselage with 84cm wing and 42 cm stabiliser will also float

Fuselage with 76 cm wing and 42 cm stabiliser will sink

so if the bolts snap, make sure you are using the 84 cm wing

interesting test, thought I'd repeat with Supercruiser
No mast - floats nicely

With mast - sinks like a stone (I do have some water in mast)

I'll be putting a leash on mine, though I do wonder if I could make the mast watertight, would that be enough.
i also wondered if I was to glue on a large Foam Foil Fangy Fillet, would that be enough? Might test that...

It worked! That is a block of high density EVA (swimming kick board) about 3cm x 20cm x 9cm. My idea is that I cut a hole out of it so it sleeves over the mast, shape to be aerodynamic and glue on with contact adhesive. I'll probably lose half that foam volume through that process, so remains to be seen if it will still float by then.
thinking further, a block of polystyrene shaped to fit, then laminated with fibreglass would be a nicer solution.

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MrA said..

thedoor said..




I had success on a different bolt that lost its head by using a smaller regular drill bit and drilling into the remaining bolt halfway, then reversing the drill and the bolt backed out nicely

I tried that when it happened on mine but I was using the lanolin grease instead of tefgel and it merely pushed the bolt further in. A left hand thread drill bit worked just fine.

Good to know. Thanks

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Stretchy said..


It worked! That is a block of high density EVA (swimming kick board) about 3cm x 20cm x 9cm. My idea is that I cut a hole out of it so it sleeves over the mast, shape to be aerodynamic and glue on with contact adhesive. I'll probably lose half that foam volume through that process, so remains to be seen if it will still float by then.
thinking further, a block of polystyrene shaped to fit, then laminated with fibreglass would be a nicer solution.

Would work, could also have some very strange effects on touchdowns if you dont shape it right (in my personal experience, round doesnt really work for example). I'd go with a drop shape or square with flattened front. For the rear not sure, if you could make it stiff amd strong enough you could make the rear a sharp straight edge at the edge of your board, just like an extension of the cutout. Would give some additional volume while floating too haha. Flattening off the back might screw up your boards shape, because it is essentially putting like a 3cm tailkick in your board behind the foilmast..

Eager to hear your results!

Stretchy, why not just a simple tether from the board to the mast in case of striking an object or box failure. This failure mode, afaik, is relevant only to Slingshot because unlike anyone else that I know, they don't use a socketed joint between the fuse and mast so the bolts take on a much larger structural role than other designs. The Cruiser (from what I can tell from photos) uses both bottom and side bolts like the Starboard freeride/race fuses do, that's much stronger than the SS design.

Does anyone else know if there are other brands susceptible to this mode of failure?

So is it recommended to change out the bolts once or twice a year?

Does salt water have anything to do with the hardware failing more than in fresh water?

Yes, salt water eases electrical currents that cause corrosion by thousands of times. There are ways to measure electrical conductivity. It does not take much electrolyte (salt) to increase the conductivity by orders of magnitude.

If you simply use stainless steel for screws and bolts, you can use aluminum and/or carbon without getting much corrosion. 316 stainless is fine for this. Some other stainlesses, too, but avoid 304 since it is like rubber.

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Paducah said..
Stretchy, why not just a simple tether from the board to the mast in case of striking an object or box failure. This failure mode, afaik, is relevant only to Slingshot because unlike anyone else that I know, they don't use a socketed joint between the fuse and mast so the bolts take on a much larger structural role than other designs. The Cruiser (from what I can tell from photos) uses both bottom and side bolts like the Starboard freeride/race fuses do, that's much stronger than the SS design.

Does anyone else know if there are other brands susceptible to this mode of failure?

Nothing wrong with a tether either, it just that I have the tendency for my mind to wander!
The issue being considered here is the mast - board connection not the mast - fuse connection, although I do wonder if the Supercruiser might actually be less vulnerable to the issue as the tuttle head is a bit longer?

The broken bolt shaft came out easily with a few taps of a sharp countersink punch to make it turn anti clockwise, then turn with fingers.

The "ezi out" left hand drill hardly scratched the surface of the titanium.

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MagicRide said..
So is it recommended to change out the bolts once or twice a year?

It seems that some people are having issues with the original slingshot bolts. If you replaced the original bolts with stainless steel ones, I am not sure if there is a need to replace them that often. I replaced the M10 for longer stainless steel ones because the originals were too short for my board; and I am replacing the ones between the mast and fuselage with stainless as well.
I don't have much idea about bolt strength besides doing a little bit of online research, but I doubt that those stainless M10 will ever break under the loads we put them under while foiling. And I know materials fatigue, but I don't think foiling year-round will break them either. For example, do boat owners with big outboard engines (a 250 hp weighs almost 300 kilos!) replace the mounting bolts annually? BTW, I do not know the answer to that.
Am I being too optimistic?

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oscardog said..
The broken bolt shaft came out easily with a few taps of a sharp countersink punch to make it turn anti clockwise, then turn with fingers.

The "ezi out" left hand drill hardly scratched the surface of the titanium.

Glad to hear you got the snapped bolt out. It is always a relief. I had the same issue with the cheap Ezi out. I had more joy with a cobalt left hand thread drill bit drilling moderately slowly and using lubrication on the bit. Only needed a bit of a hole and then it started turning the bolt.

I'm the proud owner of a new 99 wing for my Slingshot Wizard 125. I'll be using it with the 90 mast as soon as we get a little wind in Ohio. I've been using the 76 wing so far.

I'm a bit paranoid about losing my new expensive wing to a bolt failure. I snapped the bolts at the fuse-mast joint earlier this year when I grounded my foil in waist-deep water. Fortunately a swimmer found the fuse and wings on the bottom undamaged except for the sheared bolts. I'm thinking about running some strong fishing line from a rear foot strap down the mast and attaching to an unused hole in the fuse--just for insurance. I don't think the line would add too much drag.

What do you think?

Just switch the bolts to a good grade of aluminum then if you hit something they just might bend instead of snap.

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KDog said..
Just switch the bolts to a good grade of aluminum then if you hit something they just might bend instead of snap.

This is a terrible idea, do not do this!!!

AL bolts, if you could find them would be lucky to be a third of the strength of stainless bolts, and will bend and then break long before stainless ones will.

I don't see why you couldn't use some strong fishing braid.. as a backup, the drag would be negligible. Interested to know how it goes!