How to pre-calculate e-foil ride times? (Voltage, Motor, KV, Prop combos)

Good day everyone!

1st post and to this whole DYI e-foil thing

I’ve read a lot in this forum but can someone explain (demystify) a way to get a rough calculation to estimate e-foil ride times when on foil between various battery / motor size and KV / prop options out there?

There are so many options, tring to sort out which would be the optimal runtime vs weight vs power for an efoil project…

  • Which Voltage? 14S10P or 16S10P or 18S10P
  • What size motor?
  • What motor KV?
  • Propeller size and pitch based off the motor size / kv and voltage

Foil size would be based off weight but 1200cm foil for under 175lbs and 1500cm for 175-225lbs.

Any info would be greatly appreciated.

Thank you, Koa

Not an expert,

For batteries, if you want long run time go as big as you can. The extra weight won’t have much of an impact on range. Also recommend 14s as voltages above are getting a little scary with salt water.

For max run time, slower the better, so a big efficient foil.

For max range, it’s a bit tricker finding the right balance between drag and lift and speed. I’m not sure if you can calculate that easily.


You said “ Also recommend 14s as voltages above are getting a little scary with salt water.”

I’m not disputing your point about 14s being scary but I wouldn’t limit that to salt water. Actually more people are injured or worse in fresh water

The article is describing electrical socket to ground currents going through water and swimmers, it’s not the same case as getting electricity from a battery where you basically need to connect yourself in parallel to the dc circuit somehow. Therefore salt water will be worse for our use case since the issue is not conduction through a body of water to human to ground.

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Saltwater is less dangerous. The current follows the way of lowest resitance, and if your are swimming in saltwater, the water has less resistance than your body. In fresh water it is vice versa!


Exactly, but there’s a basic difference: the circuit to close with your body is not through the water to grounding earth like in a socket circuit since you have a battery. It will most likely be from hand to hand between positive and negative when you’re contacting the insides of your box somehow and it will not be while you’re in the water. While you’re on the water, even with a water filled box, the lowest resistance circuit will remain inside the box.

That is theory. i experienced it “live”. I am running 14S Li battery. My battery box is wet, my battery itself is waterproof. Once my contact got damaged, and boy, that feeling was horibble. I am driving in fresh water. You really could feel the electricity and it was not nice.And I just touched my bord, hands not even close to the battery contacts.

Ok, practice always overrules theory.

What was the circuit then?
Do you have dc connection or wires outside of the box, how did it find you as the lowest resistance path?

I assume it didn’t because he is still alive. However he was one of the paths. Think of it as an electric fence or anti-shark device. The main flow of current is designed to travel a specific path every single time (they do this by super low resistance). However if you touch either you will still get a shock because you create an alternate path. It’s just that you as the pathway will always have a higher resistance regardless of medium and as a result the current can never be lethal.

I’m more interested in the input from @Toto44, he has the info.

As mentioned my batterybox is wet. Plus and minus of the battery where not fully insulated. Just swimming next to the board was not a problem, but touching it was not nice.

Can you explain what you mean by your batterybix is wet? Is you battery sitting in water and the terminals are exposed to full water?
Thats pretty scary you got hit while in the water. I would not want to try that again!

my battery is waterproof, the batterybox is not. The contacts are amphenol waterproof ones. Before I had them, i used different ones, which where not really waterproof.

You are correct - the article is about stray A/C not D/C and I appreciate they are different.

The reason I posted in the first place was a reaction to a bunch of build plans that included very high (imo) S count batteries - this was just one of those.

It seemed that quite a few people did not share my safety concern and the comment about “salt” water being a risk triggered me to respond.

Personally I consider an electrical power source, human body and water a somewhat risky combo. Even “small “ shocks can cause serious reactions in a human.

Raising the V level in an efoil rig beyond what is required seems like a bad idea to me.

So when did you get connection? Two hands on the board while getting up, through your feet when standing, just touching the board with one hand etc?

Sorry for asking but i really want to understand this since it doesn’t seem logical and i want to put it into perspective.

i’ve gotten shocked on 20s on my ebike, with simple xt150 connectors covered in salt water, clothes and gloves being completely soaked too. Still had to get close to the connectors to get it.

I run xt150 on 12s to my efoil motor most of the time for 3 years and not a single incident.

hand s on the board or laying on the board