Hello everyone and thank you for all your contributions on this forum, it has been a great help in this process! I thought I would now contribute too.
The goal is to have a foil assist that one does not feel in the surf, to have the same freedom as prone foiling. I am mostly based in south portugal and northern spain at the moment. Waves are usually long period and heavy, from knee high to overhead. Using small foil (650 to 850), small board (4’6 33L), for 80kg rider.
The setup is heavily inspired from @Etiennebzh :
- Camdenboss CHDX8-321 and CHDX8-226C. Esc and receiver in a sub box to protect from the water drops, epoxy would also work.
- Flycolor 160A esc with radiator water cooling, capped at 60A via blheli32
- 12s2p or 12s4p batteries depending on sessions
- 6384 Saite/Flipsky
- Kparts pod and hub, 3 alu blades
- Ali waterproof connector LD28-3P between box and coiled cable to switch boxes easily
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Leash : I started with a straight cable, it got tangled in the prop and got caught in my feet on takeoff. I landed on a coiled cable 3*2.5mm from aliexpress, 2.5m extended. In the center of the coil goes a ozone wingfoil leash, made of a dyneema sheath and elastic/bungee core. This setup handles overhead breaking waves.
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Capacity : Started with molicel p45b, upgraded to samsung 50s, upgraded to solid state batteries from racepow. Those have 350wh/kp power density, 30% more than the samsungs.
Using the small box with 13ah 12s2p for 1h-1h30 session on the afs enduro 800 or silk 850, total session distance is around 16km if water is clean (half of it is surfing, half is efoiling to reconnect). Using a hip belt around 2kg.
Using the big box with 20ah 12s4p 4.5kg for 1h-1h30 session on the afs enduro 700 or silk 650, total session distance is around 20km. Also doing upwind downwinds on the enduro 800, distance is around 25km. The box is around 4.5kg, put in a 12L backpack.
- Drag : The pod and motor work great but I am probably using only up to 3000w, and the pod drag is a noticeable problem, especially on small foils where speeds can be up to 30-40kmh. The pod touch drastically increases the drag and you have to readjust the pitch mid turn.
I setup a flipsky 5085 motor on a custom pointy cone pod, and the first sessions are really impressive! It feels like half the drag at least, and less weight on the mast. Surf turns and pumping feels much more prone like. The catch is that it has less low end grunt, maybe 20%. The 800-850 foils work fine, I have yet to try the smaller foils.
If you have suggestions on a 40-50mm diameter motor that would have more torque than the flipsky 5085, please let me know! Also will work on the blades to match the motor, suggestions are welcome 
Overall it has been a game changer for my use, it has been replacing prone and wing for the most part! And building and improving the system is a great endeavor.
Happy foiling,
Rémy