With a 5" pitch propeller you will be around 25km/h with 18650 and 30 with lipo
At 37% so around 3,44v /cells you should have enough speed to fly so my guess is that the motor pulls to much amp and battery doesn’t give enough juice : this propeller has to much thrust at low rpm with its area , it is for a boat at first , try the solas ( even cut it and re shape the blade ,see my post ) , 30km/h and less amp should possible , or plug just the first printed propeller
Propeller: Good material, blade shape is not very suitable, large diameter and large pitch. Although MAT uses a plastic propeller (https://efoil.builders/uploads/default/optimized/2X/2/22fb77b91e22a123a1c8b8851e5a372ea3c9ca16_2_999x750.jpeg), which has a similar pitch, but plastic blades at max RPM partially equalize under water pressure, which will cause the propeller pitch to decrease.
If you look at the discharge graph of the mj1
https://lygte-info.dk/review/batteries2012/LG%2018650%20MJ1%203500mAh%20(Green)%20UK.html
If they discharge at 5a/cell so 60a/h with 12cells you have 1.75a around 3,4v ( 37%) which gives 21a/h for the pack : 20min of riding , Numbers kind of add up at the end
Your first built had very good efficiency
Hi Alexandre. Yeah figured I try the old prop first. I’ve modded it to fit the 80100 and it’s on the printer now, I’ll let you know if there’s any improvement. As far as the batteries go the voltage should be the same, both Lipo and Li-ion are nominal at 3.7V. The only different I can think is that the lipo continuous discharge is way higher than Li-ion. That said the LGMJ1 has a max continuous of 2.86C, so given 3.5 Amp per cell and 12 in series the pack (42Ah) should be able to supply 120 Amps continuous. I hope I’m not pulling as many as that!!? I guess I’ll make one change at a time and see what works. Also considering making a mount to run the inrunner and gearbox wet, I mean it was running wet just fine inside the pod, I just didn’t know it! This way at least I can make the mount something similar to Mat’s 80100 which will make service a breeze. It wasn’t supposed to be easy!!
I did not finish to built my 18650 pack yet with 12s16p of 30q , what i was running lipo last year , about 50h , i know that lipo are more rating discharge (min 10c), at first i was running my pack 15-20min and staid above 3.78v , at the end with skills and let then cooling a bit i was able to get Foil to 3,3v
As the graph of 18650 , they have lower C discharge more IR and more voltage sag , but they don’ t get on fire like my lipo did …
Running the mj1 at 1,5-2c is good above you loose a lot apparently and heat doesn’t help at all
It is possible to run inrunner wet , i had water in my pod almost all the Time… I just got the rear bearing rusted to the shaft and add a hard time to take it off but i guess just using corrosion X and flush it , it will ok for the season
Ok so back in business. Thanks for the help guys. I printed the same prop as with my geared setup, just with a quick 80100 mounting mod. Just back from a test ride with 20 mins on the foil and back to 30+kph with 67% battery remaining. Battery is running way cooler, so I’m pretty much back to where I was with the geared setup. Happy now! I do notice this motor sounds a bit like an old dial up modem or fax machine. Anyone else notice this?
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@foiledagain, Does it mean that on the shelf props 7.5/5 are much less efficient ?
What is this prop you just printed? Can you please share your fusion360 file with this modified prop?
Btw in your test was it opened or ducted?
I hope this works. I’m new to uploading stuff. I’m running ductless for now.
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Much appreciated! Thank you
great that work! propellers made for boat have too much trust , top speed was correct for the pitch (5") but pulling to much amp, i think we can fly with 1/3 of the blade area of those propellers
Agree
i did scale down props and still having good top speed with 135mm diameter props, and lowering amps.
That’s great news, i guess i’ll have to print your prop now 
For the noise, it might depend on the ESC…
I had strange noises and it was loosing sync at higher speed after doing a reset and not setting the timing correctly. I think i’m using 20 degrees now…
I get the strange noise depending on the prop I use. My higher pitch prop makes more noise.
@Halifax21 Darrel, I also have a Slingshot mast. Any chance I can get your file for the mast clamp? I use Fusion 360 so I’m not sure what the correct file format is but is you send me a STEP or an STL file I think I could mak that work. Thanks.
Thank you Darrel! Will start a print this afternoon.
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I love the Tampa Hackerspace orange!