I just got a Slingshot board. The tuttle bolt holes appear to be M10. My foil mast uses M6. A M6 mudguard washer mostly covers the hole. Would it be more secure if I stacked a M6 mudguard washer with a M10 regular washer?

Hello, Faff,

Suggest you go to Bunnings and get some M6 and M10 Stainless Steel washers. Fit the M6 washer onto your bolt first, then fit the M10. The SS washers have much more strength than mudguard washers.

I would think that the mudguard washers would start to distort under the load as you tighten them. This could result in a loose bolt on the water.

Also, SS resists salt water corrosion better.

Hope this helps.

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WindmanV said..
Hello, Faff,

Suggest you go to Bunnings and get some M6 and M10 Stainless Steel washers. Fit the M6 washer onto your bolt first, then fit the M10. The SS washers have much more strength than mudguard washers.

I would think that the mudguard washers would start to distort under the load as you tighten them. This could result in a loose bolt on the water.

Also, SS resists salt water corrosion better.

Hope this helps.

Thanks. It's a bit surprising though as mudguard washers are meant for this kind of situation - the hole diameter is much bigger than the bolt diameter.

If your board has chimney holes on the top, I recommend you figure out a way to load the top skin and not the inside of the chimney. I built this huge "washer" for just this very purpose. I see these on other boards around the gorge.

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segler said..
If your board has chimney holes on the top, I recommend you figure out a way to load the top skin and not the inside of the chimney. I built this huge "washer" for just this very purpose. I see these on other boards around the gorge.

I could probably coax my mechanical engineer colleagues to make one ("I bet you can't make one of these!"), but my Moses foil mast has a flange and a "beak", which surely must take some of the force.

Flange and beak do a good job of spreading the load--on the bottom. What about the top? On a foil there is a lot of down force on the back screw. Flanges and beaks do not mitigate that.

My objection to chimneys is that the down force exerted by the rear screw head is concentrated in the bottom of its chimney, even with a smallish washer in there. I don't like that. That's why I, and a bunch of other gorge foilers, spread the top load over the top skin where it belongs. Even back in the "old" days of formula racing, people were grumbling about chimneys.

Those boards with the top holes right on the skin with no chimneys have it right. You simply use big washers up there to spread those loads over the top skin, again where it belongs. It's a better design.

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segler said..
Flange and beak do a good job of spreading the load--on the bottom. What about the top? On a foil there is a lot of down force on the back screw. Flanges and beaks do not mitigate that.

My objection to chimneys is that the down force exerted by the rear screw head is concentrated in the bottom of its chimney, even with a smallish washer in there. I don't like that. That's why I, and a bunch of other gorge foilers, spread the top load over the top skin where it belongs. Even back in the "old" days of formula racing, people were grumbling about chimneys.

Those boards with the top holes right on the skin with no chimneys have it right. You simply use big washers up there to spread those loads over the top skin, again where it belongs. It's a better design.

Thanks, didn't know that... But what's the worst that can happen? As long as there's no catastrophic damage leading to foil loss, I am not too bothered. If the box is damaged, I'll get it replaced with foil tracks.

As far as the slingshot foil box goes it is built strong.
The pictures are from a green SS105 that I cut out so I could install a deep tuttle.
You can see that the box has a sandwich of some kind of G10 built right into it.
Just make sure the fender washers are wide enough as to spread the load over the top of the walls on the box.
Personally I just make washers out of G10 sheets. I have found that the 1/4 G10 washers actually fracture under very hard impacts which I think helps spread the load of the impact.

That cross-section photo shows the two chimneys, which I hate. Supposedly a "foil-ready" board will have a finbox that is stressed to carry the cantilevering loads of a foil, but I don't trust that. I have a foiling-specific board with chimneys, but I still use the big rectangular washer shown above to spread the load on the top skin of the board, where it belongs. The front screw does not really need this, but the back screw definitely does.

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WindmanV said..
Hello, Faff,

Suggest you go to Bunnings and get some M6 and M10 Stainless Steel washers. Fit the M6 washer onto your bolt first, then fit the M10. The SS washers have much more strength than mudguard washers.

I would think that the mudguard washers would start to distort under the load as you tighten them. This could result in a loose bolt on the water.

Also, SS resists salt water corrosion better.

Hope this helps.

You were right. The mudguard washers deformed after only a single use.

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segler said..
If your board has chimney holes on the top, I recommend you figure out a way to load the top skin and not the inside of the chimney. I built this huge "washer" for just this very purpose. I see these on other boards around the gorge.

I think I might have to make one of these after all. How thick is the plate? SS? Would brass or aluminium do as well?

The plate I use is 1/8 inch thick.

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segler said..
The plate I use is 1/8 inch thick.

.........or you can use a 6mm thick nylon chopping board (kitchen variety) works great, stainless mudguard washers on the bolts also.

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Te Hau said..

segler said..
The plate I use is 1/8 inch thick.

.........or you can use a 6mm thick nylon chopping board (kitchen variety) works great, stainless mudguard washers on the bolts also.

Thanks!

And I thought I was thinking outside the box - I was about to buy one of these as my "deck super washer":

www.bunnings.com.au/lemaar-300-x-75-x-2-5mm-satin-stainless-steel-push-plate_p4191402

It sounds like thick nylon will be good enough.

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segler said..
That cross-section photo shows the two chimneys, which I hate. Supposedly a "foil-ready" board will have a finbox that is stressed to carry the cantilevering loads of a foil, but I don't trust that. I have a foiling-specific board with chimneys, but I still use the big rectangular washer shown above to spread the load on the top skin of the board, where it belongs. The front screw does not really need this, but the back screw definitely does.

BTW, are there any tuttle box foil boards that don't use a chimney?

The Fanatic Stingray foilboards do NOT have chimneys. Plus, they also have dual track as well as deep tuttle. Future-proof.

Custom foilboards by Roberts and North Pacific also do NOT have chimneys.