Advice Requested - Tow boogie power and stability

Build, Repair & Mod
1

Hi all,

I’ve just taken a V2 of my tow boogie out and am having some issues. Looking for some wisdom from the forum.

First some specs (pics below):

  • Flipsky 65161 120kv motor
  • Flipsky 75200 pro V2 (watercooled type)
  • Flipsky vx3 remote
  • Rawrr mantis 72V/30Ah battery (~35 lbs)
  • Pelican 1500 case
  • Cabrinha aluminum mast
  • 10x8M-LH APC-brand propeller (most success so far)
  • 3D printed motor mount which squeezes the mast
  • Built on a 90L slingshot foil board

*i’m riding a unifoil hyper 250 in^2 (~1600 cm^2)

Now the issues:

  1. It requires a significant amount of power to get on foil. 100 amps won’t do it, 120 amps will but i’m newer to foiling (some wingfoil experience) so i continue to stall if not pumping.
  • i’ve tried a 10"x8" APC prop, fliteboard prop, and a 7.5"x7" white (aluminum) boat propeller. The boat prop pulls the hardest but requires ~120A to ride at all. The 10"x8" APC prop used to work great on my V1, but still drew higher than desirable amps at ~60A to cruise.
    In general it feels the board doesn’t move fast enough even though I believe i’ve been using larger/higher pitch props than other folks on the forum

  1. Porpoising (nose of board points up significantly). I think this can be fixed with a longer tow anchor off the back of the board.
    Open to other ideas, perhaps pitch angle of the motor/prop

  2. Significant roll. The CCW props pull left and CW prop pulls right. The higher the rpm the more significant the roll. At full tilt (both on and not on foil) the board rolls so much I can barely keep it upright by carving out in the direction required to right-it.
    Ideas i’ve read here include adding fins or trim tabs. I’ve also tried adjust yaw angle of the motor/prop but there is not a significant adjustment available with the stock foil board mounting rails.

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originally battery box lived in the hole I cut and glassed. moved it to the nose the day of testing to reduce the porpoising

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as much right-pointing yaw I could adjust. really it just looks dead straight

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estimate about 12’ of tow rope

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can anyone guess where i’ve been riding? hint: bay area

All advice and wisdom welcome, thanks!

2

another detail:

I’ve been saying 100A and 120A as thats what i’ve set my motor current limit to. I’ve confirmed this by taking data logs.

Specifically, at peak (taken from vesc tool logs):
input_voltage: 78.8
current_motor: ~117A
current_in: ~24A
erpm: ~3700 (erpm/4 pole pairs (arbitrary set in software) ~ 925rpm)
(motor and esc/mosfet temp well below limit)

If i calculated mechanical rpm correctly, for a 8" pitch prop the max speed with 100% efficiency is 7 knots. Definitely felt like that or slower.
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3

For the handling a looks like the prop is too low, which causes the nose to lift.

The back of the board needs a sharp edge as well (look at any planning boat) otherwise it will dig into the water and make the nose go up even more. Think of holding the back of a spoon into a stream of water and it will get pulled into the stream. The same thing is happening to the back of your board.