Design Info Request


Dear eFoilers,

Could you please advise me below info:

  1. At which speed the efoil board is coming out of water?
  2. What is the propeller thrust when getting out of water and at max speed?
  3. What is the difference betwwen direct drive and gearbox drive? what are the pros and cons of each system?

Best regards / Yiorgos

  1. That heavily depends on your foil (especially the front wing area). SUP foil get out much earlier than kite foils etc. I would say 8 - 12 Km/h is a good estimate.

  2. Depends on your weight, roughly 30 kg to get on the foil and 10 kg when foiling.

  3. You can find an overview over all propulsion types here: Propulsion Type Overview - Wiki
    Short version (my opinion):

Inrunner with gearbox

  • works well (many do it)
  • low drag due to small diameter
  • no cooling issues
  • low, predictable current draw -> cheaper ESC


  • high complexity (seals, couplers, bearings, gearbox)
  • high cost
  • prone to failure (gearbox wear, seals, shaft/prop unscrewing etc etc)

Direct drive outrunner with water cooling

  • works well too
  • as simple as it can get, no seals, no gearbox, very few parts to buy and assemble
  • very reliable, not much that can fail
  • cheaper overall


  • need to modify motor to prevent corrosion in the long run
  • need to have an eye on cooling (not too much epoxy)
  • need more expensive ESC that supports current limiting

As for the difference: Motors with high KV (-> high RPM) are more commonly available, but they are too fast for efficient props and have not enough torque, so we use a gearbox to reduce RPM and increase torque. Outrunners are available with very low KV and high torque so they can drive a prop directly.


Benjo thanks.
I am not too much to electronics or electric engineer.
I was thinks to design and fabricate my own board using foam and fiber glass, then buy a Chinese foil fitting an emotor with attachements and batteries which I am looking to buy from somebody.


It could be hard to find a ready-made propulsion unit + battery and ESC that doesn’t require you to know how it works and to tinker with it. Most systems from members here require frequent repairs and/or maintenance.

As for the foil, Chinese foils aren’t really cheaper (including taxes etc.) than used ones or cheap new foils, e.g. GongSUP.


I could sell you one of my propulsion units. Maintenance free, and great performance. It isn’t fully tested yet, for longevity, but it is great as it is, even though there are lots of improvements to be done. I have over 15H on my current motor with no maintenance so far in fresh water.