MAC's 2nd build

Now that the riding season is over I have several months to get ready for next summer. I am disassembling my first build to salvage what I can. I had my share of problems but it did work and I could ride on the foil for about 20 seconds without falling.

First Build summery and lessons learned.
It was made from a 8 foot long “foamy surf board” , which I don’t recommend because it will was too flexible even with reinforcement. There are 3 wood ribs that are inside the foam surf board and I drilled completely threw one of them to run my wire through. That did not help.

Chinese carbon foil with hollow aluminum mast. Lots of other guys are using the same thing here. I like it.
I think maybe I will consider shimming the rear wing because it was hard to keep the nose down.

Dry pod modified APS 83100 out-runner with internal core cooling rewired to about 116KV. I don’t believe I ever had any motor over heating problem with this set up. I did run about of spoonful of mineral oil in it. Silicon wire jackets and some rubber swells up when exposed to mineral oil. So I had tears in the wire jacket, and the rubber bladder that I used to seal the motor leads in. This let about a spoon full of water in the pod each time I rode. Once the water as in the bearings they would rust overnight.

ESC APS (about 180 Amps) first one was fried when I got into weeds. Now I have APS (16S 300/400 AMPs) One behavior I observed is they get hot when running in the battery box all closed up. My box is quite well insulated to hold things firmly. If you kill the power to the ESC while it is hot. The ESC will not restart until it cools down. Takes about 5-10 minutes. In my case, my safety lanyard kills the power to the ESC. So I end up floating around until the time pass’s.

Prop. I have always use off the shelf aluminum prop. 5" or 6".


Another observation I made on my first build. I mounded a display on my battery box to monitor voltage and current. In the bright sun I can’t read the display without kneeling on the board with my glass’s on. So on this next build there will be no visible display on the box. Also I will need to purchase some sort of water proof glass’s so I can tell how far I am above the water.

I am looking at the Eagle Tree Data Logger 150 Amp version. I hope it would allow me to learn a lot more about my set up. I know some of you have bought it. What size wires does the 150 AMP version use. Would you buy it again? Is there a better option?

At 200 pounds you can see my board bending. So I plan on being lighter next season.


Nice recap, I also plan on using the winter to make my efoil.

Thank you for this - It would never have occurred to me. I plan the same hard cutoff that you have, so I’ll need to add a small power pack of some sort to keep the cooling pump working after the cutoff.

Also, on the display issue - I’m thinking about haptics in the remote. 1 buzz at power up, 2 buzzes means something’s wrong. Not sure if it will be noticeable when you’re on the water and focused on staying out of the water.

I also had an initial design for a GIANT led display that I might go back to. I looked into several options before I gave up on an off the shelf sunlight-readable display big enough for those of us who won’t be wearing our glasses.

I wired it like this. Once I hooked up the batteries, the pump would come on every thing except the ESC would have power. Close up the box. Walk the board out to the water. Then I would plug in my safety lanyard. That energized a relay that supplied power to the ESC. The ESC outputs a frequency that turns the motor in to a speeker. The motor makes a beeping sound that indicates its ready.
I don’t like the added complexity that the safety lanyard requires but I would hate to watch the board take off by itself and hurt someone., or me.

I have those little battery cell monitors plugged in to my batteries. They make a loud and clear beep when its time to stop riding because your battery voltage is low. a loud buzzer is the way to go.

Another really good idea. I have a 12v system for the pumps, I can just leave it online and have the lanyard only cut power to the ESC. That’s just one more wire from the battery box to the ESC box.

Do you have a link to the low voltage monitor you used?


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More information on my E-foil #1

Total weight with batteries 60.6 pounds
Complete battery box fully loaded 18.8 pounds
Battery box w no batteries 8.2 pounds
Batteries 2- 6S multistar 20 AMP hours. 10C , 10.6 pounds. It appears that these 20 Amphr batteries have been discontinued now.
Foam surf board. 14.4 pounds.
Mat on top of surf board. 2 pounds The mat was made from those 2 foot by 2 foot floor padding foam tiles you put in a kids play room. Worked great, great traction, does not absorb water, soft on feet, adds buoyancy. Contact cement holds it good.
Complete foil,mast,motor assembly 21.4 pounds.
2 3/16 aluminum plates used to reinforce the surf board 4 pounds.

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Nice Mac, Its great to see you innovating on a waterproof direct drive. One tip for your next build is to move the wing back more, I have the same foil and it provides a lot of lift, this is good for stability. I have mine about 30cm from the back of the board, with my huge over 10kg battery and electronics right up front weighing it down.

Great work on what you have achieved so far!

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I had more trouble learning to ride continuously on the foil than expected. I blame

  1. It took a while just to get the board working well enough that I could use it with out working on it or waiting on parts. Whats the fun in that. 2) The surf board had so much flex in it that it was wobbly. 3) The foil was not set up as good as it could be. 4)) I don’t know what I am doing.
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No one surfs in central New York so there are not any used surf boards to be had. One of my friends had this old wind surfer siting in the weeds. Its 12 foot long and is a little heavy. I don’t love it, but its what I got.

So I cut it down to 6 foot. Bought a box that cold hold all my stuff and still sit low in the board. My goal is to have the battery/ESC box recesses in the board and directly above the mast.

now some white paint


I had good luck with my safety lanyard on my last build. It uses a magnetic switch like you would install on a window for a security system. So I just redesigned it for my new application. I filled the cavity with silicone and installed it in the board.

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Things are coming together. Waiting on some parts. Its going to weigh just under 52 pounds with out batteries. That is 2 pounds heaver than my first E-foil. This should be much more solid.
Waiting on parts.


were you expecting 52 pounds?

It would be great if it were lighter. I knew it was going to be heavier than the first one I built because the board I started with was quite solid and heavy.

My board is super-light, maybe 20 pounds, but I think it’s hollow. Once I start cutting it up I’ll need to add foam in certain areas and reinforcement in others, but I was expecting, without batteries, maybe 30 pounds? Wild guess here, I don’t actually own a scale so have no way of knowing.

But I just bumped my battery pack up from 7P to 9P so it’s going to be a very heavy pack.

I wish I had that board you have on top of your car in your build log. It does look light. Hollow might be tricky to deal with. I bought this scale. I like it. I suggest you weight things as you go, because you will wonder where all the weight came from when your done.

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