I’m taking the jet propulsion route also but from what I’ve been seeing thrust and top speed seem to be the drawbacks. Has anyone taken a look at the thrust equation T= mdot* (Ve-v1) (should look familiar if you’ve ever taken fluid dynamics class). Thrust equals mass flow rate multiplied by the difference of exit velocity and incoming velocity. Therefore in order to increase thrust one needs to increase the mass flow rate or increase the exit velocity. My plan is to increase mdot (mdot = r * V * A, densityVelocityarea). From my understanding to increase mdot increase the area which incoming fluid passes through, which also means a larger impeller. In summation has anyone taken a look at larger impellers? Most I’ve seen are around 64mm.
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exactly thats the difference between jet and openprop. Jet creates a pressure (due to smaller outlet) which results in a (higher) delta velocity. Openprop has only little pressure difference (over all, directly at the backside of the prop it might be huge) but therefore much bigger area and thus much more water moved (mdot).
So if you get a larger impeller with lower pressure/deltaV then you migh just get closer to the openprop.
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That’s a good way of thinking of it. Basically one needs to determine the ideal size of the impeller and have it still work as a jet. I guess my plan is to make a hybrid of jet propulsion and openprop is what I am hinting at. I wasn’t sure if anyone has tried this approach yet.
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Surely you’re then just getting a more inefficient Jet as well as an inefficient open prop rather than choosing one and making that more efficient? I struggle to see how you will manage to get a jet system to work well if you want to make it a hybrid with a large impeller
Sorry, hybrid was a poor choice of words on my part. In other words, I’m planning on making a larger than normal jet propulsion system than what I’ve been seeing done on hydrofoils so far. I haven’t seen a jet propulsion hydrofoil yet with the speed I’m looking for so my conclusion is that I need a larger jet.
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Yeah, sorry, I didn’t quite understand. I think what people have been finding more effective is, rather than going for a large jet, going for 2 smaller ones. Easier to keep cool with smaller motors and stuff. Look up YOUNGSTERS JET BOATS on YouTube. He is experimenting with a dual jet setup and is getting good results
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Yes I have followed Youngsters jet and chatted with him, cool jets for sure. I like the jet design efoil for its simplicity, fewer parts, and dramatically lower cost. My thoughts on the two motors, the only dual motor ESC’s I know are China made and now you doubled your jet build cost with two jet systems/motors and likely more weight having two units vs one larger one. This doubles the amount of parts, maintenance/breakdowns but double barrel jet drive is very cool as another guy built one like that…
China ESc are a struggle to keep cool and they have terrible internal resistance, running hot and seem to burst into flames easily. I’m have a custom watercooled VESC ESC, built in bec, and a true 170A continuous, and 300A peak for efoils and jet surf builds which arrives next week. Its just like the MGM-Controller ECS which gives a TRUE continuous full throttle current which it can handle without overheating but its half the cost of MGM which is really exciting and now I can limit the RPMS so I avoid over revving and cavitation, wasting power, and can also limit the current/amps to avoid extra heat, motor stress, and wasting power as well.
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At what sort of prices are custom VESC’S with 170A continuous? Can’t be cheap!! Sounds ideal though. Oneans jet systems look good and are powerful, all custom though (they suggested) from even the motor to the impeller ect…
Ill see if I can get stats like this in the next week or two when I get things back in the test tank. But Im not sure the MHZ stats are all that accurate. We have tested all the variables with their 58mm and it cavitates at 14300 - 14500 RPM no where near the 16,000 stated, and max thrust is only 27.4kg with our optimized nozzle and diffuser. Interestingly enough, the MHZ nozzle and diffuser maxed out at 25kg, well below their stated 33kg and our design out performed by 9.6%
My calculations point to the 52mm impeller only having about 18-19kg
We are now working with a professional impeller company, tomorrow we should have the results of the best impeller shape based on CFD flow,cavitation, torque and thrust from their simulation software. They ran 100 variables to find the best setup for our motor torque, impeller size, and required thrust and cruising speed. The results should populate tonight and I’m looking forward to a better more powerful jet 
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About $400 USD and the way the wires connect are with bolt/set screw, no soldering/desoldering issues to worry about.
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Would you be able to link the company website? It would be something I could look in to. That or E bike ESC’s…
The VeFoil team and I brought on an expert VESC builder to help design, test and mass produce this ESC for us which we will make available and ship worldwide within a couple months. Its a design he built and has used for a while but the custom version is specific for our purpose handling up to 100A continuous
full throttle with no water cooling required, 170A continious full throttle with water cooling running, peak 300A, max 76v, built-in BEC, on/off switch, wires bolt on vs solder connections, coated with conformal coating for water/spash resistance, all the features VESC have to offer, and nearly no internal resistance at 99.4% using all the highest quality parts available on the market for high-end. Really exciting stuff and I will share all the details because a quality ESC is the heart of an efoil or jet surfboard.
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Nice one, that sounds epic! I’ll be buying one off you when they come out then 
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we looked at a large twin 80mm jet system , bought the motors and dual esc but in the end the overall weight, size and even power was pointless. so we are trying a single prop now.
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If you want to tow pple and have lots of low end torque you need prop and reduction gear. You will never get the power you need with a jet drive for that. Don’t bother with jet FoilSurfer.
Thanks for the heads up. I’ll have to research a reduction gear that’s space friendly. Can’t fully see that option yet but yeah for keeping the rpm down, correct?
yet larger prop provides much more thrust, but you need more torque and lower rpms. That means reduction gear.
Hi Ignacio
I was wondering which motor are you using? what is the KV?
Unfortunately, the jet propulsion is a dead end. It has half the efficiency and is therefore not suitable for e-foil.
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I wouldn’t consider it a dead end! there is a commercially built foil on the market that uses jet propulsion and plenty of jet-boards!
thats like saying jet airplanes are a dead end 
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