Hi all its Alberto from Spain, after using my Slingshot Wizard 125 with a H2 wing (the blue one) for the last 12 moths I decided to upgrade my kit adding a infinity 99 wing in order to improve my perfomance in ligh winds, I am 1,95 m and 98kg so I thought i could be one of the best options to enjoy light wind sessions.
First day that I used it, after 10 minutes of foiling the two screw that join the mast and fuselage broke and thank goodness I was able to recover the wing.

I was using the 70 cm mast and the long fuselage in B position and the 42 rear wing, any ideas???? I was using the steal screws
Thanks for the feedback and sorry for my english.

It's not the most secure design anyway but any little operator error will lead to disaster. People sometimes confuse the bolts for Tuttle-mast with those for mast-fuse, and people often get one bolt cross-threaded and sort of force it in, which will lead to failure. Once one bolt goes the other is way overloaded so it wasn't necessarily both bolts that were bad in the first place.

I weigh 100kg and never broke a SS bolt, although I've since switched to Taaroa which is a little more sophisticated in design (and stiffer!). It'll be a good setup for your purposes once you sort this out, though, but I'd suggest the 91cm mast and C position will make life a lot easier.

I've used the 99 with the 42 tail (and now the 48 tail) in the most forward wing position for about a year, with a big JP 155 board and 10.5m sail. I did strip the heads of the weaker titanium bolts but after switching to stainless steel no problems with that. I also use the other slingshot wings. However, another person locally did loose their slingshot foil after bolt breakage. Because of that I use a leash to the fuselage and the drag isn't a problem really. I'm 85kgs. Other people locally have lost other brands of foils as well (an expensive sport at times!). I think sometimes it is just bad luck, like breaking an expensive high carbon mast.

Alberto, I'm glad you recovered your foil. I did the same thing with the same setup, fortunately in waist deep water. Found mine as well. You will find a wealth of info here at Seabreeze on several threads, including www.seabreeze.com.au/forums/Windsurfing/Foiling/Slingshot-titanium-bolt-failure?page=1

I suspect my bolts were slightly loose when I settled into the bottom and they snapped. Since then I use teflon tape on the threads and ensure the bolts are tight before I launch. And I check them often. I plan to move to stainless bolts like many folks here. Can someone in the U.S. post here a link for a supplier of those SS bolts--and details on what exactly to order (size, SS grade)?
Thanks!

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marc5 said..


I suspect my bolts were slightly loose when I settled into the bottom and they snapped. Since then I use teflon tape on the threads and ensure the bolts are tight before I launch. And I check them often. I plan to move to stainless bolts like many folks here. Can someone in the U.S. post here a link for a supplier of those SS bolts--and details on what exactly to order (size, SS grade)?
Thanks!

I'm not sure of the size but I've gotten a lot of spare stainless bolts from www.mcmaster.com/

You will need to order quite a few, but the price per bolt is low. I ended up sourcing a lot of spare bolts for my starboard foil this way

Make sure the mast to fuse bolts have some teflon tape or blue loctite so they do not vibrate loose while on the water.

Also agree with exploring stainless steel bolts, although I keep hearing different things on the relative strength of titanium versus stainless steel?

IMHO, the mast-fuselage connection on Slingshot wings is "under-engineered" for 90 kg+ foilers. I had repeated problems with the front screw being loose at the end of a 1-2 h session. I never had the screws break, probably because I switched to stainless steel screws (316 / A4 grade) early. I also replace the screws now more frequently, which helps a bit.

Just to clarify - when I say "under-engineered", I don't mean the system cannot be used. I have had about 200 sessions on Slingshot gear without having screws break. But proper engineering requires a decent safety multiplier - say, if you expect a 200 lb sailor to use the gear, you'd want it to be strong enough to work for a 500 lb sailor (at least components like screws). That's definitely not the case for the SS mast-fuse connection (or the fuse itself, for that matter). There have been quite a few reports from 200 lb+ guys of similar problems, while most lighter foilers never encounter any issues.

Thanks a lot guys for your help, just buy new stainless steel bolts A4 found on a local hardware store, after reading all your recomendations I am bit worried, we will see, I will keep you updated...

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albertem said..
Thanks a lot guys for your help, just buy new stainless steel bolts A4 found on a local hardware store, after reading all your recomendations I am bit worried, we will see, I will keep you updated...

A2 is 304SS, A4 is 316SS. 316 has additional moly and is a little bit stronger. Just keep an eye on things as you would other bolts.

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boardsurfr said..
IMHO, the mast-fuselage connection on Slingshot wings is "under-engineered" for 90 kg+ foilers. I had repeated problems with the front screw being loose at the end of a 1-2 h session. I never had the screws break, probably because I switched to stainless steel screws (316 / A4 grade) early. I also replace the screws now more frequently, which helps a bit.

Just to clarify - when I say "under-engineered", I don't mean the system cannot be used. I have had about 200 sessions on Slingshot gear without having screws break. But proper engineering requires a decent safety multiplier - say, if you expect a 200 lb sailor to use the gear, you'd want it to be strong enough to work for a 500 lb sailor (at least components like screws). That's definitely not the case for the SS mast-fuse connection (or the fuse itself, for that matter). There have been quite a few reports from 200 lb+ guys of similar problems, while most lighter foilers never encounter any issues.

thank you, i think this is a very good way of describing the mast to fuse connection.

I also think for this connection (and others as well), it is imperative to use good tools. The screws have to be under tension for whatever mechanical properties of the connection to take over... otherwise you're just relying on fastener strength. I see people using really wimpy allen keys or even worse #3 Phillips head screws and just getting stuff finger tight.

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albertem said..

I was using the steal screws

Glad you recovered the fuse and wings.
The quality of stainless steel screws can vary a lot.
I know there's a thread on here where others have had issues with certain brands of screws
and recommended a place to buy quality screw from.

I have made several videos on the i99 wing as it has been by far one of the most asked about SS wings, I have truly put the i99 through its paces in every wind strength from 8-20 knots.

At the time of most of the videos I was closer to 92kg+ with wetsuit and harness etc.

Over the course of nearly 2 years I have not experienced a single bolt break or come loose.

Several reasons! I believe fresh water is a lot less stress on hardware in general . I don't have scientific proof on that, but I do have a collective group of 10 foilers all using slingshot with zero issues.

Now I live and foil in the salty waters of Florida and in last 8 weeks I had bolts seize, and wing cap strip out. I have now established a more rigorous maintenance program with constant cleaning and replacing the anti seize grease.

I also replace most major foil bolts twice per year (each time change) some people think it's over kill but that's up to you.

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albertem said..
Thanks a lot guys for your help, just buy new stainless steel bolts A4 found on a local hardware store, after reading all your recomendations I am bit worried, we will see, I will keep you updated...

www.mcmaster.com/93395A425/

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sunsetsailboards said..

boardsurfr said..
IMHO, the mast-fuselage connection on Slingshot wings is "under-engineered" for 90 kg+ foilers. I had repeated problems with the front screw being loose at the end of a 1-2 h session. I never had the screws break, probably because I switched to stainless steel screws (316 / A4 grade) early. I also replace the screws now more frequently, which helps a bit.

Just to clarify - when I say "under-engineered", I don't mean the system cannot be used. I have had about 200 sessions on Slingshot gear without having screws break. But proper engineering requires a decent safety multiplier - say, if you expect a 200 lb sailor to use the gear, you'd want it to be strong enough to work for a 500 lb sailor (at least components like screws). That's definitely not the case for the SS mast-fuse connection (or the fuse itself, for that matter). There have been quite a few reports from 200 lb+ guys of similar problems, while most lighter foilers never encounter any issues.

thank you, i think this is a very good way of describing the mast to fuse connection.

I also think for this connection (and others as well), it is imperative to use good tools. The screws have to be under tension for whatever mechanical properties of the connection to take over... otherwise you're just relying on fastener strength. I see people using really wimpy allen keys or even worse #3 Phillips head screws and just getting stuff finger tight.

Theres tight, then theres over tight. I actually stopped using instruments i could get a lot of torque on after i sheared a bolt in two whilst tensioning it up. Had i stopped torquing it a split second earlier i would've gone foiling with a stretched bolt on the verge of snapping. I just use a spinner handle on them now.

These days i bump things around as im tensioning them lightly and slowly, i don't rely on the bolt to tow things together. You want things to mate together completely so there's no slack in the join, then make sure the bolt is tight. Now generally when i come in the bolts are all still as tight as i did them up.


i'd probably be a bit more liberal with tension if bolts were bigger than m6, but that unfortunately seems to have pretty much been adopted as industry standard.

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sunsetsailboards said..
I also think for this connection (and others as well), it is imperative to use good tools. The screws have to be under tension for whatever mechanical properties of the connection to take over... otherwise you're just relying on fastener strength. I see people using really wimpy allen keys or even worse #3 Phillips head screws and just getting stuff finger tight.

Good point. I replaced my allen keys right away with stainless ones from Wera, although mostly because the SS keys started rusting right away. With one set of screws that probably were very slightly bent, no amount of force would prevent the screws from coming loose, though.

Interestingly enough, I use a lot less force when assembling my Starboard GT-R+ foil. I've only had a few sessions on it, but I never had a single screw come loose on it. I'm less worried because there is quite a bit of redundancy, for example 3 screws + 2 bolts from the side for the mast-fuse connection, in addition to a tight fit of the mast head in the fuse. But I have the suspicion that the steel-to-steel connections are also superior to steel-to-aluminum connections.

Tefgel on all the fasteners makes a huge difference all around, regardless of Slingshot vs. Starboard foils.

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boardsurfr said..

sunsetsailboards said..
I also think for this connection (and others as well), it is imperative to use good tools. The screws have to be under tension for whatever mechanical properties of the connection to take over... otherwise you're just relying on fastener strength. I see people using really wimpy allen keys or even worse #3 Phillips head screws and just getting stuff finger tight.

Good point. I replaced my allen keys right away with stainless ones from Wera, although mostly because the SS keys started rusting right away. With one set of screws that probably were very slightly bent, no amount of force would prevent the screws from coming loose, though.

Interestingly enough, I use a lot less force when assembling my Starboard GT-R+ foil. I've only had a few sessions on it, but I never had a single screw come loose on it. I'm less worried because there is quite a bit of redundancy, for example 3 screws + 2 bolts from the side for the mast-fuse connection, in addition to a tight fit of the mast head in the fuse. But I have the suspicion that the steel-to-steel connections are also superior to steel-to-aluminum connections.

The engineering on starboard foils is infinitely better than slingshot. I treat my starboard in ways that would have killed my slingshot stuff.
With slingshot it's crucial to wiggle the components as you tighten to make sure everything settles into place since only the taper of the bolts holds things together.

I was originally going to replace my SS bolts too, due to reading posts like these. But after talking to my local shop that sells SS gear, they told me I shouldn't need to replace these bolts. They should last for years they told me. I'm in my 2nd season and nothing has broke nor ever came loose. I might replace them for the 3rd season, but I will assess the wear at that time.

Hi, finally I could remove the screw from the mast and I think that I know what was the problem and the reason of the broken bolt.
I am not allow to upload pictures as a new member but you can see that the broken bolts are much shorter than the new one (and I was using the right bolts), so the problem probably was due to the vibrations the bolts loosen and then broke.I did not use any tape for the bolts.

General rule, as you know, lightweights generally do no stress equipment, unless they are pushing the limits.
Big sailors DO stress their gear. As a heavyweight, you should manage your gear with more attention and more often.