Will the mast hold up?

Please tell me your opinion! I am not here to show off, I want feedback. : )

So I am planning on mounting the mast to the two aluminium profiles with 4xM8 screws that go through the profile. I am not using the slots for anything. The Profiles will be wraped in fibre glass and get epoxied into the channels at the bottom, followed by 1 layer of 6oz or 200g/m2 fibreglass around the entire board. The bolts are added from the deck side and will get large washers so they don´t dig into the Aluminium/Fibreglass. Do you recon that is a good idea? I hope the aluminium would destribute the load a little bit. However, the two profiles are not strong enough to support my weight on their own. They bend. I could add a few carbon fibre golf club shafts to the board.

I am not that experienced with large fibreglass structures. I only did repairs in the past, so it is hard to judge if this is enough or not.

The board is 156x52x12cm and made from CNC cut XPS. The mast has 3 positions and is drawn to scale.

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Hi Max. I would use at least two layers of 6oz glass on the top. With just one layer you will likely get pressure dents in the deck of the board from knees, heels etc. Also XPS foam has a tendency to delaminate from the resin and fibreglass layer. From what I have read it is recommended to sand the surface with a low grit sandpaper 20/40 grit to make heaps of scratches so the resin can penetrate the foam better. I don’t think you will need the carbon fibre golf shafts. I would add an extra patch of glass each side where the foil is going to go as well. Cheers

I really don’t see the point of the aluminium I dont think its going to acheave a hole lot and if anything just overcomplicating it and giving a point of failure and added drag. With a xps blank you could actually just install two fin boxes with a layer of glass under and 3 over and job done. ( I have done this and it works fine) Like mentioned the bond of glass to xps is not good on its own what you do need to do with xps is get a spiked roller and go over the entire blank so that you get some resin penetrating the surface to stop it from delaminating to easy. If you wanted to go one stage further use a block of high density foam inserted into the board and then route you finboxes in.


2x 6oz is not a problem. Glass is cheap. I was also playing with the idea of routing in some 2mm deep round chanels into the deck. That would give it a 3D structure and reinforce it a little more. An easy thing to do for the CNC, but might be trickier for glassing.

I will use a spike roller, but since the foam gets CNC cut, it should have a rough finish anyway. Where exactly would that “patch” go? Around the section where the mast is like a belt?

The aluminium will be entirely glassed over just like a fin box. There will be glass underneath and on top, so at the end it will be just like a very long fin box. Instead of foam its aluminium. I am using it because I have tons lying around and the profile has a lot of surfac area. So it won´t add any extra drag. They will be hidden inside. I want to avoid this: https://www.swaylocks.com/sites/default/files/IMG_4021.PNG

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The cnc finnish will need to be sanded smooth first or the glass will not sit directly againt the foam and you will get air bubbles and most likely a lot of sand throughs when you come to sand the hot coat. Personally I think you are just creating more work for yourself and adding a lot of unnecessary work. Installing two 10.5" fin boxes is cheap fast light and proven to work.

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@MaxMaker about the pic, “MeToo” :joy::rofl::joy:

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Hi there, this is quite similar to what i did, two lengths of extrusion with 4 m8 stainless bolts slotted. for more strength i bolted the aluminium extrusion too a pair of blocks of wood that went all the way through the board and made contact with the fiberglass on the top of the board. i then filled any little gaps with epoxy and applied 2 layers on top and 3 layers on the bottom followed with 2-3 layers of top coat and alot of sanding.

final result was super strong, my reasons where because i was afraid the two extrusions on the bottom wouldnt be strong enough and cause de-lamination between the bottom layers.

cheers, David.

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There’s a reason no one puts aluminum stringers in surfboards.

I’d go with no stringer (that’s what a longitudinal stiffening insert is called in a surfboard) and a heavier layup (the layers of glass/carbon). Charlie has built dozens of boards and repaired hundreds. Trust him. I’ve built a few myself. At the thickness you are working, there’s no need for inserts or channels. The board at 4" thick is a giant flattened tube and so it’ll be super stiff on its own. And yes, those features are way harder to glass and sand.

If you want a bullet proof board, go with 2 layers of 6oz glass with another layer in a patch where you stand for the top. 2 x 6oz for the bottom and nothing will hurt that board. Simple, inexpensive, and proven in surfing and standup paddleboards for years.

If you build out of EPS foam, put in a Gore-Tex vent too.

There’s a lot to figure out on these builds, but the board construction is really simple. I’d save the innovation and experimentation for propulsion, that’s what’s never been done.

But don’t let us stop you if you really want to learn to build boards. It’s fun and mistakes are educational! :wink:

Hope this helps.


I need something that can withstand the compression forces of the bolts though. I could use wood also instead of Aluminium. Otherwise I fear the bolt heads will destroy the foam and finreglass sandwich.

Why do you think the aluminium will cause problems? If you look at Pacificmeisters thread, he ripped his mast out which could cause a short circuit. He hit a rock though.

Hey MaxMaker you can always use through bolts with a slight recess on the top. Epoxy a tube of stainless or bronze into an oversized hole and put two layers of glass at the top and bottom. you can also add big stainless steel fender washers. It will not rip out unless you hit something super solid. I did this on on old kite board for learning how to foil and it works fine. Even having the the bolt heads exposed is not such a big deal.

That would have been my second choice, but I figured that those 8 metal inserts (3 positions) would weigh almost as much as the the 2 profiles. The profiles would add to the overall stability though.

Just not convinced, based on all the surf foils we are seeing, that the bolt through is needed.

Look at all the surf foil setups and they are using the foam cassette set into the bottom. I’m not saying this is the end all, but if you do want a bolt through you could simply put a plywood veneer on the top and bolt to that. Easy and maybe a wider spreading of the load. Just a thought.

Google “Austin Kalama” and check out his videos and pics. He’s jumping and flipping a foil board sometimes 6-8 feet (over 2 meters) and landing and not braking the foil off. His is foam and glass mounted in a Tuttle box.

Hmm, that is true. Ill try it I guess. If this foil works out, i will probably build a Carbon vs too sometime.