”The barge” efoil build

[larsb]

Building a foil board, first attempt. How hard can it be?
I have very limited time so i’ll build quickly and to learn more than to do a beautiful design, it’s now called ”the barge build”

Took about an hour to build a hot wire foam cutter so i am off to a flying start.

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I found Gong surfs/foils on the web and have ordered this xxl size foil after some emailing back and forth:

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It will be powered by a c80100 motor setup so i’ll have to waterproof one of my motors, coming soon

[DogDipstick]

Building a foil board, first attempt. How hard can it be?

I have a lot of experience in building boats, rc motors, batteries and the like. Got a good foam cutter, lol. Look forward to seeing how you go. I have been entertaining the idea of the same thing, .

[larsb]

The barge foam design:

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Basic dimensions 1700x580x150mm, 120 L

[larsb]

First foam glue and cutting done, i got some issues. Three stacked foam sheets of 50mm hardly works as their tolerances are too large. There will be gaps - i have used 3m 77 spray adhesive which is not gap filling and instantly tacks so repositioning is not possible. I’ll try a foaming PUR adhesive instead but i have doubts it will work well while sanding and hotwire cutting.

I might try also to also find thicker xps foam sheets to solve the stacking gap issue, should be better with only two sheets stacked

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[larsb]

Got new xps sheets and sikabond-545 (ordinary PUR) glue. Hopes are high.

Will make a new attempt at gluing the slabs on sunday when it’s raining.

[larsb]

Made a smaller hot wire bow for shorter cut depths, this is about 30cm/12” wide and can do 30cm deep cuts. It turns the wire red hot.. dimmer does not affect either voltage or current.

Seems the dimmer cannot regulate the power supply. Guess they’re not compatible. Why?

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Cutting with the longer bow is slow, the power i've got is struggling with 75cm/30” wire, cuts are slow through the foam even though they burn the wood guides i made. I guess the melting/gassing of the foam cools too much over too long width. Power is 19V*3.9A so 74W. Maybe i’ll have to use metal cutting guides and more power. but that requires another power supply or a battery.

[larsb]

Testing cuts on ordinary EPS80. It’s a lot easier than cutting XPS300 due to the lower density.

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I think the hot wire calculator i used is not for XPS as it gives out too low power values.
(https://jacobs-online.biz/nichrome/NichromeCalc.html)
I guess more like 150w is needed to take a full width cut through 24”/600mm XPS300 sheets.

[larsb]

Well, temperature of the short bow really is too high, i started a fire when cutting I got no pictures of that though, had to save the board

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I made some guide rails with metal strapping fixed with hot glue dots. Worked remarkably well!

[larsb]

I couldn’t wait for the PUR glue to set in 24 hours and the new XPS sheets (jackofoam XPS250) turned out to be a lot better in the dimensions so i decided to give the super 77 adhesive another chance bonding time is then reduced to 30 minutes which is nice.
I sanded hairlines and small ridges created during the manufacturing of the sheets to get better flatness, took about 2 minutes per sheet

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The slabs are bonding as we speak and i’m already happy with the result. Cowabunga!

I think i’ll scrap the CAD designing and just freebase with the hotwire bow and metal strapping, it was quick and a lot more fun.

[larsb]

Since dimmer doesn’t work i’ll need to solve it with longer wire. Hacked up a new 50cm bow which gives the thread a really dark cherry color. I’d guess max temperature is around 450-500 deg C. No more fires

Incandescent color vs temperature

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Mid size / 500mm bow

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[larsb]

All the hotwire cuts are now done, just some rounding of the corners is needed before glassing. I had a lot of fun with it!

The gluing turned out to be sh*t (again), i sprayed heavier coats than before with the super 77 and it seems the foam melted a bit. Aaargh! The sheets are now only partially glued - It’ll have to do anyway though far from optimal. Tomorrow is sanding time.

[larsb]

Sanding halfway completed. Not going for the gold just barely OK looks
I wonder how to fill small voids in the foam.. best would be something that sands as easy as the foam itself. it’ll have to be a quick solution. Maybe epoxy putty if result doesn't need sanding at all, or some other ultralight sandable filler.

[larsb]

I've ordered some heavy glass fibre cloth: https://shop1.r-g.de/en/art/190156

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It's 600g/m2, goal is to do 1 reinforcement layer + 1 top layer with this and glass it in one layup only.

[larsb]

Got an IP67 electronics enclosure. A bit lazy to not build it but making a DIY 100% waterproof seal is not easy.

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[larsb]

This guy knows what he's doing, love to see a pro do his work.

[larsb]

I couldn't open the enclosure for the life of me, then i saw the lid bulged inwards by half an inch, there was so high vacuum in it that i had to heat it for five minutes with a hairdryer before the suction let go

I guess tightness is proven so that's good

[larsb]

Got the foil today it’s humongous
Came packaged in a super nice bag with separate foam sheets for the fuselage, mast, front and rear wing. Build quality is good - way better than my expectations.

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One thing to improve: The fuselage is 30x30 solid alu, weighs a ton and could easily be replaced. Carbon variant of this or even a drilled out one would shed a pound or two.

[larsb]

I am thinking about how to connect the phase wires, there’s plenty of space inside the mast even for 8AWG wires but not for connectors. I also want to be able to separate the mast and board with no connectors in the water.

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Guess i’ll do a larger through hole from the top of the board and a small recess in the bottom to get into the mast somehow. I want to keep the flow as good as possible around the mast.

[larsb]

First prop on the way.

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Don’t know yet if the support structure can be removed

[larsb]

Support material was sticking so it looks a bit rough, i’ll try to finish it with carbon and epoxy. It’s still quite strong!

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Later on i’ll print some other props also, that’s the big question for the drive system.

[amberwolf]

The gluing turned out to be sh*t (again), i sprayed heavier coats than before with the super 77 and it seems the foam melted a bit.

I have found with Super77 and similar spray glues that it works best if you spray it on boht surfaces, let it dry just to tacky, and *then* stick them together.

[larsb]

Yep, that’s what i did. The confusing thing is that 3m77 spray was foam safe historically but now exists in two variants due to california environmental regulations, one with acetone in it (that can barely be used on foam if very careful) and then the old formula.

There’s also 3m78 that’s specific for foams but i don’t find anyone who sells it.

The foam melted in the middle of the sheets, i think it might have been ok if i let them air even more before assembling. You live, you learn

[larsb]

Battery doesn’t fit in the box height or width in the way i wanted as the lid protrudes inside the wall of the bottom part. It doesn’t matter, i have some room to spare, i’ll rotate it and cut away part of the lid. I planned an alu plate lid for better heat exchange anyway

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[amberwolf]

Yep, that’s what i did. The confusing thing is that 3m77 spray was foam safe historically but now exists in two variants due to california environmental regulations, one with acetone in it (that can barely be used on foam if very careful) and then the old formula.

Ah...I've never run into the acetone variant. :/ The old formula always worked fine on everything, though getting it off of *you* was a huge PITA if overspray got beyond your gloves/etc.

I used to use it on a lot of sci-fi props and such, most especially to put printed labels on things, whcih I could then clearcoat with Krylon to ensure they didn't wear away easily, where necessary. But also useful just for securing things like foam layers for cores and molds together prior to sculpting.

There’s also 3m78 that’s specific for foams but i don’t find anyone who sells it.

https://www.amazon.com/3M-78-Polystyren ... B001EUOAGK
Terrible price, but at least they have it, as long as you're not on Catalina Island.

[larsb]

”Unavailable” to me in sweden..