Equipment: Total Cost: ~ $1087
- Fresh water (I live in Missouri)
-old kneeboard I had laying around - $0
-Hydrofoil- Gong Allvator Rise M70 (front wing 70cm wide, volume1500cm², rear wing 45cm wide, volume 270cm², Mast - 80cm (select the “kitefoil” for the 80cm mast) $342.49 (shipping included)
-44.4v 12s 2kwh li-ion battery (used ev battery from batteryhookup.com) - $200
-130kv 65121 flipsky brushless motor, 3700w peak, 2000w continuous - $269
-Flipsky FS75100 ESC ( uses open source VESC software) - $130
-Apache 3800 water proof box - $54
-moto z2 force ( VESC display - any old android phone) $0
-8awg silicon wire to extend motor wires $69 (this was 50’ so I have a lot left over)
-motor mount (mast clamp) - pine 2x4 and aluminum flashing I had laying around, I may attempt to 3D print a better solution in the future.
-propeller - 7 1/2 x 7 propeller that was included with the flipsky 65121 motor, it is far too big. I’ve cut it down to about 110cm or 4.33" - I’m currently only getting about 1500rpm drawing 70 amps from the battery (50v fully charged). This motor has ~5N/M or torque, its bigger brother, the 65161 has ~9N/M or torque from what I’ve read.
I haven’t gotten up on it under its own power yet. I’m still tweaking things. I think I may need a bigger surf board.
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I can only load one photo at a time because I’m a new user, although I’ve been lurking for at least 3 years enjoying all of your posts!
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My mast clamp looks pretty janky, but it is actually quite solid! It’s made from a pine 2x4 and some aluminum flashing.
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Here’s a screen capture from a 30 second ride showing my power usage and rpm ( divide erpm by 6) so I peaked just under 2000 rpm pulling around 80 amps from the battery, I have the motor amperage limited to 120amps. I required an assist from a boat to get going, although once up I do have enough power to ride. Does anyone think a 2 blade prop would give me better efficiency? I then removed the prop and rode behind the boat, and I have to say, the motor does add a lot of drag. I plan to 3d print a better mount, change to a paddle board so I can start standing up, and find or print a 2 blade propeller. Any ideas or suggestions are appreciated!
Here is the link to the screen capture of my vesc data.
https://youtu.be/RdkGFFX5u68
Sorry about the low quality, not sure why it is so grainy. I also have a video of the ride, will post it later.
I think maybe your board is too small to get on foil for the amount of power avaliable. For reference I need 180 - 200A at 16s to get up on foil with a 5ft board 130mm thick at 115kg. Once on foil it drops down to 30 - 40ish amps. A bigger board, more streamline motor mount and better prop will definitely help
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Thanks for the reference point, that helps! I weigh 80kg and my board weighs 30kg, so pretty similar. I have different batteries that could save about 5kg at the expense of range as well.
Lol I mean my fat ass alone weighes in at 115kg 
. Board with bat and foil is roughly 30kg.
Question for others using VESC regarding motor RPM.
I’m running at 50 volts, My ERPM is maxing out at 18000 which indicates 3000 rpm 18000/6 poles is 3000rpm, I’ve verified that is correct using an android app that uses a strobe light function to check rpm (really easy effective way to check rpm). With a 130kv motor I should get 6500rpm at 50v right? I measured ~30v AC between motor wires at full throttle. Am I missing something? Is the KV rating wrong? What should the voltage between two of the motor wires be from the ESC at 100% duty cycle? I’m in FOC mode, max ERPM is set to 50k, and I’ve checked other minimums to see if something is limiting my rpm.
Success! The two blade propeller did the trick. VIDEO LINK ABOVE
The two blade 9-spline propeller fits my flipsky 65121 motor with only very minor modification and some electrical tape on the shaft to make it fit snug, also adds some dampening. It was originally 7x4 3/4 but I cut it down to 6" diameter, crude hack saw job but there doesn’t seem to be any vibration!
I had longer rides, but that was the only one that I got on camera.
Takes 75amps to get on foil, then it drops down to 30 or so.
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Here is another video, with VESC real time data. About a one minute ride. I need to add some water cooling or improve my passive cooling.
Adding water cooling. I could have bought a CPU cooler but I like to use what I have lying around. Going to test it out later today hopefully!
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I had a breakthrough today! I was really unstable, like a tail heavy airplane, and I couldnt get my weight far enough forward without bending my really soft paddle board. I had no trouble riding this board being pulled behind the boat. So I tried a smaller battery I had laying around. Saved about 10 kg, or 20lbs, and voila! I could fly immediately. My highest speed was about at 25kph (15mph), although I’m sure I can go faster, the end of the pond comes quickly, looking forward to a run in the river!
44v 2kwh 12s-1p li-ion - 26lb - $250
48v 0.3kwh 13s-4p li-ion - 7lbs - $30 - great deal! You could definitely stack these.
I bought both of these batteries on batteryhookup.com
With the heavy battery my foil board weighs 85lb (38kg) with the lighter battery it weighs 59lb ( 26kg) big difference!
Obviously 300wh (0.3kwh) is about 1/6 the energy capacity of the bigger battery, but I still rode for about 30 minutes! Obviously some.putting around too, and swimming back to the board… I also have several of the smaller batteries ( I use them for ebikes) so I can swap them out easily rather than recharging.
My water cooling works well! It didn’t initially until I added thermal paste to the mating surfaces. the ESC starts limiting power when it gets to 75c, which used to happen rather quickly, but now it doesn’t get over 45c. I didnt use a pump, I drilled a hole in the mast clamp just in front of the bolt head, the water travels up through the mast channel, into a tube, through the heat sink, and then down through the other channel. The water exits at the bottom of the channel where I drilled a small hole, it’s on the rear mast channel so there is a Venturi effect to help suck water through.
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According to your pict n°6, it seems that the hole is perpendicular to the water stream which is better against clogging but not as powerful as a hole inline with the water stream which might be overkill though. Do you still have enough pressure ?
The exit hole would be underwater then ? Would you have a picture ?
You can see the exit hole in my last picture on the bottom right side of the mast. The amount of water flow required is very small, water has a large thermal density, so any flow at all works just fine. And yes, soefoil, If I remove the return line, I can visualize water trickling out when I’m riding. The return hose probably isn’t necessary, but I thought I might be when riding high on the foil, and I didn’t want to take it apart again, So I just did both.
I had the foil off the board last night to replace my aluminum plate with a 5’ plank for improved rigidity, so I decided to enlarge the water cooling supply hose for kicks.
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Swapping the aluminum plate for the 3/4" x 11" x5’ pine plank has made the very flexible paddle board very rigid and only added 3 lbs. There is a little more drag as well on takeoff, but the rigidity is very nice. I moved my box to get the battery in the right spot for center of gravity and now I can ride with the bigger 26lb ( 11.7kg) 44v 40ah 2kwh battery! I am much more agile and get on foil much quicker with the smaller battery 7lb, 48v, 6.25ah, 0.3kwh. I get 10-15 minutes of run time with the smaller battery, and over an hour on the bigger battery. I spent about 2 hours on the water this morning 
, and I didn’t burn a drop of gasoline! This is what it’s all about!
The video below is using the small battery. I weigh 175lb, my board weighs 62lbs with the small battery, 88lbs with the big battery. I do notice some obvious sway in the 80cm v1 gong aluminum mast with the heavier battery when riding high. My next build will definitely use a more Ridgid mast. Somewhere between a total weight (rider + foil board) of 237lb (107kg) to 263lb ( 119.5kg) the swaying becomes very noticeable.
With the heavier battery, I have to go faster, (somewhere around 20kph but I’m not sure completely sure) to stay on the foil, and use around 1600 watts, with the lighter battery, I can foil a bit slower and use only 1400 watts. I think a bigger foil would be better for the heavier setup.
My water cooling works seems to be working well, although it did run warmer today than my previous test, It seemed to be staying in the 50c range on rides over 5 minutes and once on an extended run I got up to 75c and had to stop, but it was because my hose got loose, it cooled off very quickly once corrected.
To Do List:
- Optimizing my propeller. I like the 2 blade prop, but I suspect there is room for improvement.
- Build a new board from scratch, or maybe just build a compartment in this board to hide the battery and 3d print a waterproof ESC box. My waterproof box weighs 8lb, so this would save a not insignificant amount of weight, plus then I could float the board upside down through the shallows of the river.
- Get metr.at for improved data collection, or figure out the VESC data recording
- Record my maximum speed.
- Attempt to get this board licensed and legal. Missouri, USA requires anything with mechanical propulsion to be registered and licensed.
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Efoil Build in Missouri V2
60"x24"x6" or ~ (150x60x15cm) ~ 135L
Battery compartment that is waterproof enough for fresh water.
I was a little concerned the construction styrofoam would be too soft, but it has worked just fine.
I had some sheets of this laying around so I decided to use it to build a new board, I would recommend a foam with more compressive strength, but it has worked fine so far, The strength is in the fiberglass shell. I also used cheap tabletop epoxy that I got off ebay, because I had it laying around. I think the only difference in marine epoxy is the added UV protection, which I don’t care about since I’m painting the board. I’m pretty happy with the results given this is my first surfboard build. I used 3 layers over the foil box, and two layers where I stand. I painted it with a urethane primer. I got the hatch from ebay.
https://www.youtube.com/watch?v=X9RhmLanXAs
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That’s a simple solution. Your front square corners will make touch downs more brutal. What is your “board only” weight ?
Hatch: check waterproofness twice as these don’t have such a good reputation. Some members have replaced the gasket by an insulating one.
Use a paper towel and try to make your board sink before putting on your electronic equipment.
