Is there a way to estimate the thrust of a setup?

Hi, here again with the janky, cheapo E-surf build.

I’m again considering different motors and batteries to buy, and have come here for a bit of insight. Right now my plan is to buy 4 Turnigy 20,000mAh Li-Po batteries, and wire them in 2x2 for around 44V, with 40,000mAh of charge. First of all, is this viable? I’d like smaller batteries wired together so I can use them in other projects aswell, therefore I’m not a big fan of a huge Li-Ion pack.

But the real question I have is about the motors. I’m looking at either a Flipsky 65161 120KV 6000W with the prop, or the huge 85135 140KV 12000W one. Any recommendations? Note that a surfboard will require much more thrust than an E-foil.

Is there a formula or a calculator online to estimate the thrust on one of these badboys running at 44V, maybe 120A?

Cheers!

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To be honest i think you would need 5 of those Turnigy Lipos in parallel and then series them for 12S and that may not even be good enough lol. They’re more like 1 or 2C not 12C. For anything half fun you would probably need 16KW+ of power and at 12s thats over 300 Amps assuming you’re using a Jet Pump

The batterys are more like 3-4c based on some tests ive seen from an old esk8 form

To answer your question about thrust. There is a very nice web tool that can somewhat do this: This propeller generation website run by Caeses (well known propeller design software) is free to use. You just input your motor parameters, your wanted propeller size, and it simply generates a propeller geometry for you, and calculates the efficiency and thrust. Depending on your vessel speed, the propeller will have a different pitch, which is mainly what limits your thrust.

You can also do some math. Most propellers are around 50-70% efficient (source).
If your motor power is P, and your vessel speed is v, the thrust T would be equal to:

T = propeller efficiency * P / v

For example, let’s assume 60% prop efficiency. If your motor power is 6000W and your desired vessel speed is 6 m/s (12 knots) the thrust would be 600 N or 60 kg of force. If your surfboard needs more thrust, you must use a lower pitch propeller and your top speed will be lower.
Static thrust is harder to approximate. Hope this answer will help you.

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If/when you have a working setup, to get the static thrust, you can apply the board nose pressure against a bathroom scale (not necessarily waterproof) against a pontoon or a swimming pool wall.
This static thrust or Bollard push is given in kg, @Frage’s in 2018 measured 42kg of static thrust 117Amps 4200W.