Boris eFoil attempt: planing but not flying

Hi all,

I bought a wingset this summer, so am taking this eSUP to the next level. Here are my details:

  • FSESC 200A
  • 2x 6S batteries in series (~50V)
  • VX3 remote
  • FS 65161 and FS stock propeller
  • Naish Thrust Windsurf 2019 wingset

Here are the results of my trial:

  • I managed to hit about 15 km/h max speed on full throttle, drawing about 3 kW.
  • I was planing, but definitely not fully out of the water on top of the foil. I had mine on the least lift-y setting.
  • I blew my kill switch again – prior trial blew the SSR, this time used a MOSFET. Both died in a way that freaks me out: the circuit is just closed so that the circuit is just closed permanently, kill switch does nothing when disconnected. Seems like a really scary failure mode.
  • ESC heated up to like 70C and the box on my board was very very hot.

I have some questions for the community:

  • Do you think I should change props? Any thoughts on the stock prop? Folks seem to be using the FlyingRodeo (FR) one, but they seem to be out of stock. Any comparable ones? Or is someone willing to share a printable 3D model? Maybe someone can scan their FR with their handy LIDAR iPhone scanner app?
  • Are you using water cooling? I’m debating between that (the Flipsky ESC I use has water cooling support) and mounting components onto a large aluminium plate.
  • At what speed do you expect to have full lift-off? Should I adjust the back wing angle of attack? Is the foil wingset a good choice for this?
  • I used a VX3 this time since I had major issues with my remote last summer. But this remote receiver plugs into the same port as the bluetooth module, so now I have no way to log trial data. Anyone have a workaround?

Some pics:

Screen Shot 2021-06-22 at 10.02.20 PM Screen Shot 2021-06-22 at 10.02.31 PM Screen Shot 2021-06-22 at 10.02.08 PM

Many thanks!

1 Like

I think you are close, wing should be ok with 1200cm2. With 15km/h you are very close to take off speed. If you remove the duct and change to a smaller diameter prop you sould get flying. Flite propeller is available but neds to be reamed/drilled out to fit the 12mm shaft.

For the kill switch I suggest either using a 200A fuse or a contacter (works but is heavy and adds weight). Those FET switches are well known to burn and if they burn they stay closed.
Fuse: IMAXX MDP200: KFZ-Sicherung, midiOTO, 200 A, 58 V, violett bei reichelt elektronik
Fuseholder: IMAXX HMD1: KFZ-Sicherungshalter, midiOTO, 200 A, 58 V, Schraubanschluss bei reichelt elektronik

US $15.12 16% Off | SW180 NO (normally open ) style 12V 24V 36V 48V 60V 72V 200A DC Contactor ZJW200A for forklift handling wehicle car winch

12V coil
With the contactor it is getting a little bit complicated, you need 12V plus a smal relay to switch it on, as the holding current is around 1A.
I built a circuit with an arduino and 2 small relays and an antispark resistor. It can be switched on with a 433Mhz garage dor opening remote. It works but it is a bit overengineered, I would just use a Fuse, if that burns, it interrups the connection

What is the purpose of the kill switch?
I would suggest you to go for a normal boat kill switch (closing) and use the kill switch feature in the vesc project that will come in next release.
Kill switch feature through adc input | VESC Project (
It was discussed in this thread also.
75v & 300a vesc (vesc75/300) - / Electronics (ESC, remote, batteries) -

1 Like

@sat_be Thanks for the link to the switch – definitely need normally open. Bummer about needing to be drilled. How to do that without ruining the balance of the prop?

I don’t want to remove the duct for safety reasons. Do you think it would cause so much drag? Any other suggestions from a safety perspective?

I’m already using a 200A fuse, but that’s not what I mean by kill switch.

@heddan99 I have a leash that connects to the control line for the FET/SSR. The load line of that connects to the ESC circuit. The point is I want that ESC unpowered if I fall off the board. I had a bad experience with a sketchy remote (before I bought VX3) and I’m not sure it’s going to do the right thing.

Any thoughts on cooling? Gonna attempt to mount to an aluminum plate – water cooling seems more complicated.

To drill out the hole of the Flite prop, it is best to do it on a lathe. Machine a piece to hold it from the back, fix it with glue that can be removed, i.e. soft loctite. Then ream or lathe it to 12mm from the other side (front, side that faces towards the motor).
Yes I think your duct is a show stopper, the profile needs to be much more aquadynamic. You could try to adapt @pacificmeister’s parametric duct to fit your propeller. The gap between the duct and the propeller should be as small as possible, 0.5-1mm, therefore you need to choose the prop first.
I also started with a duct for security reasons but finally got rid of it (as many others as well). The sharp edges of the foil and mast are a bigger risk for injury.
@pacificmeister parametric duct: Parametric Propeller & Duct Design - Fusion 360 - #3 by pacificmeister

It looks like you have a lot of things wires, wire ties, and any thing else in the water. The drag will reduce your speed and those extra tenths will make a difference. If you can clean up your setup it may help. Good luck.

Your mast is right at the back of the board, but that’s probably just windsurf style - and made up for with a huuge long fuselage. Are you putting your weight back enough to allow take off? 15kmhr should be plenty for a big surf wing.

@wushbush Thanks, good point. Cleaned that up.

@sat_be Ordered a contactor too (this one: 200A 12,000W, 12kW NO Contactor | Electric Car Parts Co)

Going to try to run it from a 12V pack of batteries, but might not have enough current… In this case planning to to buy a 48V => 12V converter and power it from my main battery… anyone have this setup?

Once that’s setup and well tested, I’ll be more comfortable removing the duct.

@Jatem yes indeed, I bought the board from a windsurfer guy. I’ve been putting weight on front for now, since there’s a lot of weight on the back already. Got more tips about technique? Or links? Much appreciated.

Why not operate the contactor directly from the main battery, as is available 12-120V versions?

Mainly I’m concerned that my kill switch circuit would blow at 48V. I think it’s rated for 12V. Thoughts? Here’s the unit:

Don know the current draw at 48 V but should be rather limited just to operate the contactor. The kill switch is just a switch, its not limited to 12V, believe how much current it can handle is also related to voltage. This switch is rated for 5a 12V, cant imagine the contactor would use that much. would probably wire it directly from the main battery, obviously do some testing and measuring of the current to operate the contactor.
Edit. The specks says Maximum Coil Energy Draw: 15W. should be 0,31 amp at 48V?

@smus Hi, I think I saw a guy using a 48v cheap e-bike controller using the 12v rail, basically an improvised dc-dc concerter, I can’t tell exactly how but I think it’s possible, I need a converter too, it’s been such a long time and I still haven’t ordered one yet :unamused:

12V and 5V: DC-DC Buck Converter 12V-60V To 5V 12V Dual Output Step Down Voltage Regulator | eBay
12V only:

Yers, the way @jeffM does it using a 48V 100A Kilovac relay, controlled by a 48V lanyard kill switch then drills the Flite 8mm prop to 12mm:


1 Like

Hey Boris, any improvement yet ? Following as I am building my first efoil. Thanks

Welcome @alexander1

Quick update…

  1. I’ve cleaned up wires so that they produce less drag
  2. Installed this new kill switch which is purely mechanical, so no more fried SSRs and MOSFETs
  3. Removed the duct (YOLO)

I still haven’t had a chance to try this on the water tho – too busy with work and life and then it got cold here in Seattle. So basically either I need to start wearing a wet suit and taking days off, or wait for the weather to warm back up (~6mo).

My main question is safety, especially with no more duct. I think the new kill switch should be fine under load, but am a bit worried about the open circuit when the motor is killed by the kill switch, in terms of sparking and/or producing an undesirable short. Especially because… This is Water.

Safety aside, hopefully my modifications will give me enough juice to get up on the wing. If not, I’ll probably need to consider a new prop. If yes, I’ll buy a couple 20Ah batteries and replace my current 6.5Ah setup, triple my battery life and finally learn how to efoil :slight_smile:


Those wires on the trailing edge are an absolute killer. It would probably be less shit if on the leading edge, and you could encase them in 3d printed covers, like seen on someone’s build here.
Best advice before you try to efoil, and even more so before you DIY efoil, is to learn basic foiling skills first. Take your setup behind a boat, a winch or an ebike somewhere and practice the feel for it, get to know its lift profile, get an idea of take off speed and stall speed, sweet spot, etc… And you can do all of this before your setup is ready.


Hi @smus, I think I have the same Naish Thrust foil as you, and thought I would need to cut off the vertical fin, as it might get in the way?

Thanks for the tip. I’ll move the wires to the front if I’m failing to get up still.