Installing a Kill Switch

EFOIL.builders Electronics (ESC, remote, batteries)
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I don’t know if this is exactly what you need, but I have drawn a quick shematic on how to switch such big relays with an arduino before here: Pacificmeister Build Info and CAD Sources - #298 by Flo - Builds - FOIL.zone .
But this schematic is only good if you do the antispark routine in software, like MaxMaker does it. PowerGlider’s solution above is more bulletproof.
As his LTSpice Simulation does not state actual components for the Mosfet used, I did a quick search for a fitting one. Probably most Mosfets that have a breakdown voltage higher than the battery voltage plus the inductive peak from switching off will work, after all the continous current through the Fet is only about 1A.
The first suitable device I found was this one: https://de.farnell.com/on-semiconductor/fdp3651u/mosfet-n-kanal-to-220/dp/1324799
But really depending on your electronics knowledge you might need more of a real schematic including Mosfet control, etc. To build the Solution by PowerGlider above.

I would not recommend using half the pack voltage for the relay. For me the 5 to 10Watts I remember that those relays pull cause too much of an imbalance in the pack. I would rather use a cheap buck converter set to 24 volts from the full pack voltage.

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Great idea to have a look at the built electronics. It seems my resistors have infinite resistance. It should have been 3 times 4.7Ohm in parallel, so 1.56Ohms. I think the constant rated power loss is 1 W per resistor, it seems not enough. Maybe they were overloaded when the manual switch was chattering. Single switching i tested initially.
The Transistor is from a BMS, N-Fet 60V, you need two resistors and a 10V zener diode to control and protect the gate. I need to investigate further.

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I have a flier boat 320a ESC. I just installed 2 reed switches.

1 to turn on/off my water pump for cooling(I can switch it off when the board is out of the water)

Another one to cut the signal to the esc. It works reliable all the time. The motor stops within a second or so. Also; Once you’re a bit more experienced you know when you will fall and then you get your finger of the trigger.

You can see in the video below that I connected the deadmans cord with sticky band to my foot.

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