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.
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.
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.
I was thinking about building it this way too, but then decided to take the “under board mounted” Foil Assist route due to safety concerns. I was thinking of solutions but came to the end that I prefer to have a board between me and a burning assist.
But I would love to give the body mounted assist a try one day as I can see the advantages it has → less swing weight and bigger battery
How do you manage the risks of a burning esc and potentially battery?
Hello Rémy!
Great to see you here. Amazing work. I will switch to 5085 too and probably improve my leash. One day I will even charge balanced… looking forward to meet you again.
Regards, Robert from Austria
The esc is in a sub-box in the main box, glued to an alu radiator that is water cooled outside the box, and it is supposed to stop operating if its temperature is above 90 degrees (blheli settings)
Several friends and I have been using and abusing this system for a year now, so far no overheating. A friend had his box flooded, the batteries (samsungs) got hot and it turned back, that’s it. The solid state batteries are supposedly even safer for fire/explosions, I think it is relatively safe, although I could be wrong.
Yes, batteries should not start to burn even when under water regardless the chemistry. From my research and calculation putting an xt90 of a 12s pack into salt water would cause a current flow of around 7A. It would just drain your battery and corrode the contacts. But I have not verified in real life yet, so I could be wrong. Your friends experience backs that up though. I was just measuring the resistance between the contacts of a drowned xt90 in salt and fresh water.
So from my point of view the single risk is the esc catching fire and in the worst case causing the batteries to burn down too.
Seperating the esc into a sub-box that probably holds back the fire from the batteries is a good idea
Hi Remi, awesome system you got! I see that you are riding closed to sagres. Planning to come with my foil soon, woluld be cool if we can meet and share a session
Trying to update my assist as well, especially on the connectors side. Can i ask if you got the LD28 docking version? Or one of the other versions?
Can i ask for the reference of the ali coiled (cant find it) and the length of your ozone wingfoil leash? Is it the one size wing leash ?
Hello, I am in Santander at the moment unfortunately. Usually in south portugal winter time. It’s the LD28 docking, longest version of the 3 options. For the cable, 3core 13AWG, stretch 2 meter (actual uncoiled length is about 3.5m), https://es.aliexpress.com/item/1005003176716502.html?spm=a2g0o.order_list.order_list_main.85.5d361802lU2K4D&gatewayAdapt=glo2esp
For the ozone wingfoil leash (one size I think), I cut it about 20% so that maximum stretched length is 2 meters, coiled cable is 2.5m, this way it takes all the force and protects the coiled cable.
Thanks for posting all the detail. 13awg at 3.5 is a long cable, do you notice it getting warm at all? Maybe the lower current draw of the 5085 motor helps with this.
I’ve noticed my 13awg shorter cable gets quite warm to the touch with 6374 Flipsky motor and twin blade genuine black FOil Drive prop blades.
Looks like you on to a great build .
Do you think the 5085 motor would have enough grunt to get a 95kg rider onto foil? I’m mostly using UHA 870 or 670 when waves are bigger. I like the idea of less drag on mast with smaller motor but don’t know if it would have enough power to get me up?
Hey Astan! Have you played around with a foil assist already? It depends on how many amps you need at 44v. If you have good technique to avoid flat water start, using waves to get on foil, and get the speed from the wave and pumping before efoiling, I suspect it’s possible at least on the 870.
A little on assists but more on my boogie. My assist I built was over powered with 160amp esc with 6384 motor on 12s but I’ve just finished the in board build with a vesc and yet to test. Only thing is after foiling behind boogie on prone board it’s hard to go to assist again I’m after the more natural feel assist. I have ordered motor and vesc and will give it a try cheers for advice I think your right with good technique it might still work
Looking forward to see you again! 
