MACs 3rd and probably not the last build

My first build looked like this. It worked. It needed several improvements. But it worked sometimes. image

My 2nd build looked like this, It worked good, it is dependable. I am keeping it as is so I have something to ride if I give up on my 3rd build.

Things I would like to address in my 3rd build.

  1. The battery and all the electronics weight was slightly aft of the center of the mast on my 2nd build. I believe this caused me to have to stand farther fwd than ideal.
  2. It was heavier than I would like. 69.2 pounds with 14S12P 30Q battery.
  3. I would like to improve the ride so I felt more comfortable going a little faster.

I was hoping Peter was going to be able to offer the motor he had been working on. Any interest in custom Direct Drive Inrunner

I also tried to get motor and prop information from David at FR website. He did not respond.

So I went with the Flipsky 65161/120KV and the Flipsky 200 amp water cooled VESC.

Knowing that phase current is normally higher than battery current, does anyone know why Flipsky makes the 3 phase wires 10 AWG, and the battery wires are doubled up 8AWG.

Anyone see the logic in this? There are 2 large water inputs, and 2 small water outputs.

Nice looking builds!

You really made a lot of progress between your first and second build. I’m looking forward to seeing your third build.

As far as your riding position. The center of mass of the combined board and battery and components should be as close to centered over the front wing. However this weight being a bit too far back does not have enough of of an impact to cause the “on the nose” riding position.

What type of foil are you using? Most foil manufacturers don’t like to talk about “trimming” anymore. But, believe it or not…most wings, and most setups would benefit from being trimmed.
Some designs are really easy to trim the rear wing and some are next to impossible.

On my slingshot wings it’s easy to trim. The rear wing on most foils is set at about 3° pitch down. This helps overcome the drag of the mast and wings through the water and forces the front wing to pitch up and want to rise out of the water. This pitch down of the rear wing, to some extent is needed but it creates a loss of performance due to its lift being down instead of up, requiring more overall lift, and in turn more drag.

I use a small washer under the front bolt of the rear wing, and play with the pitch. Somewhere between 3° pitch down and 1° pitch down usually works best.


No idea on this, found it strange myself but I looped the 2 ins together as they are all interconnected so my out is now a in and an out.

my idea:

8awg for continious current load (reduce IR and spikes) and 10awg motor side for “pulse” current as each phase doesn’t see continious load

2 in/outlet for 2 row of fets to cool
outlet smaller to decrease flow and allow water to stay “longer” and take the heat


Sounds plausible! :rofl::call_me_hand:

I was using that Chinese foil that many others here use. I tried 2 washers under the stab. That was way too much. One washer worked good once I got use to it. I think part of my problem is when the nose comes down to horizontal the board speeds up. Takes me out of my comfort zone.

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Thanks for taking a stab at it, but I don’t know. When doing heavy loaded bench test I have observed that my phase wires get much warmer than my battery wires. All wires were 8 AWG, You might be right, they did it for a reason. Just don’t know yet.

I am thinking you might be right about the cooling lines. The restricted smaller output lines might be to insure that at certain input flow the heat exchange stays full of water and does not partially empty out. If it was not full of water it would not work nearly as well.
Its still strange that the manufacturer would do the things they do with no explanation. Its just asking for people to do something wrong.

I never heard of CorrosionX before I started reading this forum. You guys talk so highly of it I bought some and filled the 65161 motor with it. It was in the aerosol form, I sprayed it in and poured it out several times.
The motor front end pulled off with little effort. The razor blades easily pried the front off. After the front pulls out about 1/4" then you need to fight the magnets to pull the rotor out the rest of the way.
The motor rotor measures 1.25" in diameter, and the rotor magnet length is 4".


I decided to build the board from scratch. Its really hard to do and I don’t recommend it. Its winter here and Epoxy does not harden in the cold. Lots of problems. I only show the good stuff.
My board is going to be 5 foot long, 24" wide, 4" thick. I started with a 4’ x 8’ -2" thick XPS from home depot. I cut it to size and glued the pieces together. Here I am testing to see how strong the table is.


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Nice! Yes. Sooooo much work. The abuse of the table is awesome. :rofl::+1:

Looking good!

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Good work! I was also having issues with the temperature in my basement in winter, 15 degrees gives you more time to work with epoxy but it’s not good to cure it. I wrapped an electric blanket around and then put some more insulation around it, temp got to 40 degrees Celsius which was good for the epoxy to cure.

Yes. That electric blanket idea was a game changer. The Epoxy went from sticky for a week, to solid overnight. It worked really well.

More progress photos, Things always look better in the photos than they really look.



May I ask what oz did you use and how many layers?

I did 1 layer on the bottom, and then 1 layer on the top. So the sides are 2 layers thick. The electrical compartment cover is 7 layers thick (I would go 10 if I did it again). The box that is the electrical enclosure and provides a lot of the strength for the board is on average about 3 to layers thick. The area where the mast will mount will be reinforced with 2 1/4" plywood pieces to hold Anchor nuts. It seems to be all very strong but this is the first board I have ever built and I am making it up as I go.

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Today I glued in the plywood and anchors for the mast. Weights holding things in place while the epoxy drys. All the greenish clouds are automobile spot putty used to fill in voids.

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Working on drilling my mast. Stressful operation.