Seattle USA Converting Windfoil (Windsurf Foil Board) into E-Foil when not enough wind using Trolling Motor

I have started a while ago a Blog / Topic in our Pacific North West Windtalk Forum for Windsurfers and Windfoilers frustrated with not enough wind around Seattle Metropolitan Area under title:

“How to quickly convert your Windsurf Foil Board into Electric Foil Board for around $1500 - DIY - Methodology behind”

All the details: “The Journey”, “Progress” & applied “Learning” is documented there.

Here I am only posting some highlights only.

Basic concept is based on adding quick “bolt on” or “snap on” attachments to my both Slingshot Flyer 280 Windfoil Board & to Exocet RF91 Windfoil Board to add 24V 160LB Trolling motors.

Testing so far is with POER 1500W and Caroute N300 2100W Trolling Motors

I am using also two separate sets (each set 2*12V) of Lithium Batteries at 60AH & 150AH.
One set I waterproofed myself adapting Plano Boxes, The second came with waterproof cases.

I have recently added some more innovative solution how to lower the foiling speed taking advantage of more thrust and lower speeds from Trolling Motors.

More details in another Blog / Topic:
“WWII Sinking the battleship Bismarck - Inspired by British Torpedo Bombers - What does it have to do with Slingshot Hydrofoil ?”

I am currently in the process of getting an issue fixed with Caroute N300 Motor where it seem to be running in protection mode whenever I put it in the water meaning only few percent of power is being applied.

I have already experimented with variety propellers with different pitch & sizes from variety of Brands: original POER & Caroute, Watersnake, Torqeedo (several versions).

I am getting very close to the foiling speeds but I am not there yet.
Need more powerful Caroute 2100W Trolling Motor to be fixed & another Torqeedo Propeller to arrive.

Testing on the water is done on Lake Washington Seattle at OO Denny Park:

With the buoy and anchor at chest deep it is much easier to change for example motor and propeller instead of taking entire board out of the water.

I am getting close to 6.0 mph speeds, need to get to somewhere close to 7-8 mph to get my “bi-plane foil mod” to take effect.
It has been proven by a Friend of mine also using Slingshot Flyer 280 and Infiniti 84 single wing that you need about 9 mph speed to get to foiling which the following video is a proof of:

I will provide major updates here while the detailed updates are being done on NW Windtalk Forum:

I think what a few have failed to realise while going the trolling motor route, is that an e-foil motor is actually a top of the range high performance motor that would greatly improve a trolling motor.
With this in mind I doubt you will find a trolling motor that is truly capable of allowing you to e-foil properly. It’s always going to be under powered and on the slower side, even if you do get up.
On the power requirement side ±4Kw makes it easy to start and then ±2kw to cruise around. Some with the larger wings use less than 2kw, but I find that to get a nice ride you tend to sit around the 2Kw area.

From my perspective the main challenge with trolling motors is a little bit different.
More sophisticated, supposedly more efficient and more powerful brushless / commuterless Trolling
Motors have automatic features like “weeds on propeller detection” and in many conditions where motor is going into so called “protection mode” limiting output power. The real challenge is to find an optimal propeller that is not too big (in both blade size and pitch) that will not trigger auto power reduction or in other trolling motors complete shut down at the same time it will reach high RPM range where the Electric Motors deliver most of the power, and also not too small to reach max RPMs without providing sufficient thrust.
My whole project started from simple estimation. I am heavy at 100kg / 220LB and together with my wife we were using Watersnake T24 (24 LB of thrust 240W) commutator / brushed (less efficient) trolling Motor with our Huge Hobby Oasis Tandem kayak and were able to reach 3 to 4 mph speeds for extended periods of time. Some Trolling Motor companies advertise their motors to be 240 LB of thrust (1500W) & 160LB of thrust (2100W) so you do the math. I should be easily able to reach 9MPH where it is proven that a windsurf foilboard with a hydrofoil (much less drag and weight than tandem kayak with two people) lifts even heavier person out of the water.
My challenge is to even get any close to max draw current specified by sellers of these motors.
You can read more details on

Have you tried to switch the propeller to a rc airplane Apc prop ?

To maximize your watts, you could try to decrease the power train drag: here on the tube between motor and battery: a rod has 12 times the drag of an airfoil section having same thickness. That would be like having two masts…
With a bit of work, you could combine both masts in a single one: the motor cables going through the mast using the Fliteboard/Pegasus way or fitting the motor in a cylinder + nose (the eTakuma way) …

I would like to make it more Educational for Everyone answering Alexandre question.
Actually quite to the opposite, I purposefully am not going to go any airplane propeller route.
Though "theoretical science" and airplane prop design software may lead you into narrow and long blade propellers as the most efficient but let me ask the question: How many times is water more dense than air ? The “practical science” dictates something opposite.
Another question: Which from all 7 propellers I have been testing, you think, is allowing maximum speed for my windsurf hydrofoil to still work without tripping on either “weed shut down” or “power reduction protection mode”?

It is a Watersnake and despite its larger hub adding to drag the short wide blades get more speed than Caroute & POER Motor original propellers (perfectly matched hub size narrower longer blades).
Unfortunately Torqeedo regular & high speed propellers trigger “weed shutdown” on POER 1500W Motor that has higher RPMs at 2500 vs Torqeedo Cruise Motor at 1300 and Caroute at 1500.
The next step will be to reduce propeller diameter by shaving off its tips of prop blades.
Why ? because the further you go from the shaft on propeller blade the more linear speed in the water therefore drag goes to the square of the speed.
The way to go is either totally convert trolling motor with higher RPM using gearbox to increase torque
to existing prop, which I do not want to do at this point, or to customize the existing higher pitch prop by reducing its diameter (making blades shorter maintaining their width & pitch).
That is why existing e-foil boards propellers are on the opposite end of the spectrum from airplane props.

SoEFoil brings a good point. I will consider in the future either flattening lower part of Trolling Motor shaft or building aluminum casing like a hydrofoil mast around it.
Again, I want to make minimal modifications to the Trolling Motor as possible so it can still be used as a Trolling Motor when we use our Hobie Oasis Tandem Kayak with my wife on the water.

To your question : hard to say for a that pic may be the 2 blades prop?
Yes I know about air prop design but still it works pretty well in water and I will give it a shot one day in the name of science …

POER 240LB (?!) 1500W Motor update:

Getting closer and closer to complete foiling with just weaker POER Motor advertised as 1500W but its manual says 45A max * 24V that means 1080W while in my backyard large tub testing I was able to draw only 21A (504W) in forward direction and 26A (624W) in reverse direction maximum.

Caroute 160LB 2100W Motor update:
In the meantime I am working with Caroute Technical Support. My 2100W N300 Motor is continuously running in Protection Mode every time it is in the water drawing at max only around 5A with the smallest 3 wing prop from the picture you have earlier seen. Propeller is from POER Motor 240mm (9.4") diameter and pitch estimated at about 6" (150mm). Larger props it only draws 1A.
Caroute Technical Support believes ESC (controller) has an issue and replacement is on its way.
They authorized me also to pull the motor apart and they examined detailed pictures. They also authorized me to replace the ESC. BTW: I will need to use QSI Potting Material, 2-Part, QSil 553 to seal the ESC inside the Motor Hub later when it arrives.

In the meantime I tested another “bi-plane mod” configuration with weaker POER Motor

More details at:
“WWII Sinking the battleship Bismarck - Inspired by British Torpedo Bombers - What does it have to do with Slingshot Hydrofoil ?”

Have you tried increasing the foil area… like…significantly?
Ask the stingrays and skates how they generate lift with almost no forward motion.
Start with too much area…square shape… big span…big chord.
Just get it to fly with your current propulsion system.
Then, reduce each dimension until it begins to fly lower.
Then, reduce chord and increase span areas, in equal area amounts.
More chord = more lift
More span = more stability
More of both = lower takeoff speed / less required power , for stable flight / lower top end
You can use a flat piece plywood, but you will need to shave the leading and trailing top edges down and increase the angle of attack VERY slightly (1 degree or less), to generate lift with very little forward motion.
Start with a span and chord the length/width of your body height and reduce area from there.
The downside is that, using only one wing, it will surface plane at normal speeds.
The solution there is to use multiple wings , totaling the required area for low speed takeoff, at the depth where each upper wing touches the surface.
There will be a pulse when each wing touches surface.
Use diagonals for smooth speed/lift transition .
see drawing.