We have built a dual motor tow boogie with Flipsky 6384 motors, kparts 3 blade counter rotating props, 75100 v2 Pro Vescs, Bremote v2 and 12s4p battery. Although my son was riding behind it today on foil (he is <60kg), it defintely requires some tuning as it is not tame. It has a tendency to lift the port side with the prop coming clear of the water. It was worse when he was out on the starboard side which I expect, but it was still happening when he was straight behind it, and it the starboard side stayed firmly in the water when he was on the port side. Props are counter rotating inwards at the top. Weight is centred, and i don’t see any obvious misalignment, so not sure how to solve this. My only guess is that perhaps the port motorpod is slightly angled out (out at the front and in at the back), so when it has a slight roll then the motor pod essentially acts as a foil and lifts the port side up. Do people normally angle the motor pods inwards at the bow? Any other suggestions?
I would bring the props as close together as possible on the center line, and print some trim tabs for the corners of the board here to direct the flow down slightly.
Props should counter rotate outwards. Boats run them like this to prevent capsizing forces
You will see a bit change spinning outwards. And a lower traction point on the end of your aft bar. Use a stainless steel M8 threaded eye under water (7 to 10 cm).
Thanks all for the tips. I went for the easy option first and swapped the props to spin outwards as a first step. It helps a bit, but we still managed to flip it at 60% throttle while towing. Swapped props seem to a give a bit more steering authority when towing. It works fine at 60% throttle for getting my 60kg son up, but at 90kg and full throttle I end up ventilating the props even at low speed while trying to get on the foil (normally only one ventilates at a time). Perhaps it is sucking air down from the side of the board? I have moved the weight as far forward as I can go (without nosediving), which is better at speed. I will also try and shim the mast mounts to see if motor angle change helps. @Strongarm, I am at 310mm centres at the moment, and I think they are 140mm props. What would you recommend, 250mm between centres, or even less? I was hoping this might help with ventilation too.
Strongarm gave you effective and practical advice. Install trim tabs on the aft edges. This will eliminate stern lift when turning and ventilation. Trim off any protruding mast sections. Installing shims under the motors is ineffective since they are centered.
Lowering the towing point is also effective. On one of my bodyboards, I had a hole drilled in the trimmer and a tow rope threaded through it. So, reading this thread, I thought I should do something more elegant. An eye bolt, a Nordic walking pole, and a unique ) piece connecting these. What do you think? And thanks to Etiennebzh for the advice with the bolt.
Eyebolt is cheap, no drag and you can just pass your rope through and connect to the tow bar if you’re afraid to bend it.
That is a neat motor mount and looks like a good way to prevent ventilation down the motor mount mast. Good point about the shims. Does your lowered tow point drag in the water with bolt or adapter design, as I see that mine is below or just above the water without one? Or perhaps this is self-correcting and the lower tow point just means the bow drops, which raises the tow point to the same place, but now with better board trim? The eye bolt design looks good.