Really nicely documented. Well done.
What’s your GPS setup? I am using the MRo u-Blox Neo-M9N 10Hz and it performs really well. Beautiful GPS position and speed data. You need to have the antenna pointed upwards and avoid blocking it with CF, but with those considerations, it’s bulletproof.
I can foil at around 850W, cruising speed about 20-25 km/h with Gong Curve MT and FS65161 120kv 14S. FR 6" prop and flow optimized motor mount. Looking forward to your test results!
Which speed at a 850W power draw ?
@3rd_ave_Lien, Gong Xover XL foil 1900cm2, 65161 100KV motor, Yamaha 6" prop: 7.8-8kmh, cables still outside the mast ?
@jkoljo , 70kg, Gong Curve MT 1150cm2, 65161 120KV motor, FR 6" prop: 20-25kmh, cables inside the mast.
The thin profile of the Gong Curve MT 1150cm2 has far less drag than the Xover XL one.
Yes, cables still outside. More experimental results will follow… This is just the beginning.
Thanks for the GPS info, I’ll let my assistant respond, 
Foiling results to follow soon, I hope.
The GPS is on a Lilygo TTGO T-SIM7000G SIM GPS. I modified their demo program to write time, Latitude and longitude directly to an SD card. The device is ESP32 based and the board has a battery holder on the back. I am not using the SIM, but did check that it worked.
Hi jkoljo,
This is what I mean concerning the GPS:
(This is a recording of today’s session. In that segment i’m planning/surfing but not on foil. Measurements are taken at 2s intervals.)
Perhaps it could be a bit smoother. On the other hand you have a long data set and a low sampling rate, so some part of that speed variation is probably real data as well.
GPS units often report data slower than what they spec, since the receiving conditions and the antenna design are usually less than ideal. Maybe you could try a more robust and faster GPS like the MRo M9N. It’s quite easy to interface with, just pre-configure it with the uBlox u-center software and then read data via UBX or NMEA protocol at your desired baud (TTL UART). Both are well documented. The GPS streams data so you don’t even have to poll it. This should get you closer to 10 Hz, depending on the receiving conditions. Then you can apply a low pass filter if you like to get it even smoother.
I am now using a 1500 cm2 wing I borrowed. I will definitely buy a Gong Curve MT next winter, when I go to France. (I get my Gong equipment when visiting France. But where can you buy it in the US?
Unless there is a yet better wing you can recommend?
gong-galaxy.com is the place. They ship worldwide and if you’re in the US, you don’t pay the 20% VAT that is displayed (All tax included)
A wing to recommend ? Not particularly. The curve MT is IMHO a good choice. If you’re light (100-120lbs 50-60kg) you could try a ST in the 800cm2 range for even less drag but a higher take-off speed. For even less drag, there is the Fluid M range offering thinner and lower volume wings, never tested on a efoil here if I’m not mistaken. This 2022 Fluid range is more tolerant than Veloce M wings.
Routing the cables inside the mast will definitely remove a lot of drag and unlock the potential of M or S wings.
[Edit: Veloce S+M range added
Thank you ! I just ordered a GONG Curve MT. They have 20% off till the end of the month, code UPGRADE-OCTOBER
I would like to use that code too, but all I want is out of stock 
Couldn’t you just order and pay, and they will send once available? I think for some of my previous orders I did in same manner
No way. Says out of stock, Preorder not possible
Updated battery wiring
After failing miserably in our attempt to elegantly position the ESC on a heavy metal plate under the board for cooling, our 2nd build locates the ESC and a waterpump in the battery suitcase, which is now the “everything” suitcase. (Pictures in previous posts).
Here is the updated everything case schematic :
(details upon request):
May I suggest a last test ? Your most efficient 6" Yamaha prop cut at different diametres, max diam down to 110mm (say), to show the influence of this parametre on max speed and power draw… and locate the sweet spot !
Yes, we’ll do that. We had to solve some problems first, but now we’re back in business. Planning to run the tests in the following days.
Great experiment Lien! Power vs Speed, 2 remarks:
We are going to redo all these tests. The initial build had the wires outside the mast, and because of the drag, the results are probably not reliable. Easier to redo the test than trying to figure out what’s wrong…
Boating - Latest data:
This graph is for “boating mode”, not foiling, not even planing. It stops at 15 km/h because at that point, I’d be foiling.
I use it to get an idea of how much power I’ll need to get to eFoiling speed. But ultimately, I’m more interested in the power in foiling mode.
Which is fine, because these “boating” curves have to be taken with a grain of salt. I obtained them by fitting the function P = Cm * RPM**2.7 into the experimental data. For example, below: in blue the data, in red, the fitted curve.
Foiling: the power drops sharply when I get on foil. So I can use these curves (power and speed vs. time) to qualify the wing+propeller pair.
For now, I’m using Yamaha propellers that we cut to various diameters. That was not perfect, so there’s nothing definitive about these results.
I could tell while riding that the D=7.25" propeller was no good. This is confirmed by the collected data.
The D=5.5" and D=6" were similarly pleasant to ride, but the plot shows that the 6" is more efficient.
