Electric boats 'safe' voltage

Not against the spark situation.

In automotive applications sparks are not an issue. Sparks in motors, alternators, relays and similar are present in the engine compartments of vehicles with 12 volt systems. The difference from boats is there is generally very little possibility of flamable vapors accumulating without a massive fuel leak.

In boats there is a long history of fires and explosions caused by sparks in 12 volt devices in the presence of accumulated flamable vapors. So whether the electrical system is 12 volts, 50 volts or 500 volts the possibility ofsparks in the engine compartment and bilges should to be eliminated.

 

Sparks might not be a concern if the OP is building an all electric boat, so long as there's no flammable Vapors around? If the potential sparking is a concern and coming from switches, why not use one of the many different Spark suppression designs? JMHO.

 

It's not really a spark issue but a personnel safety issue. It is the current that injures or kills people and voltage is current*resistance. Yes a 12V or even a 9V can injure you if you short it directly pole-to-pole, and I have a burn scar to prove it. However, if the current must return through very high resistance, air, clothing, shoes, etc; then the current is greatly reduced as is the likelihood of injury. So for "low voltage" systems, accidentally brushing against an exposed conductor has a very low chance of having a current of any significant strength return to complete the circuit. For "high voltage" systems even as low as 120VAC, touching a screwdriver against a hot lead can kill, and so much more so for 240 and 480 commonly found on ships (which are wired 'delta' BTW to try to prevent this accidental sort of thing). And this is also why insulation over wires is typically measured in Mega-ohms...

 

9 Volt Battery Myths And Facts – The Safety Brief https://safetybrief.creativesafetysupply.com/9-volt-battery-myths-and-facts/

FWIW..

 

I'm no closer to understanding whether my 72 volt/3 kW motor with its 20aH lithium ion battery is likely to kill me in a boat and what I can do to mitigate the risks. This kit is used on small electric motocross bikes, and they get wet, but not usually with salt water.

 

My opinion is it depends on how you build it it when you adapt the kit to a boat situation. Some quick ideas:

Place all live electrical components in positions where they are least likely to undergo splashing and especially submersion, and use well insulated wiring and shielding.

There should be no bare metal sections or contacts associated with the hot circuitry that can be touched or brushed against, accidentally or momemtarily by man or conducting objects or tools.

Add Fast response circuit breakers, fuses or GFCI, to protect against Short circuits or accidental contact with hot electrical circuits.

Do regular inspections to find and remove any salt water puddling within the the boat which can cause corrosion; delicate electrical components and circuitry should be hermetically sealed if at all possible, as even a saltwater atmosphere can cause corrosion in air exposed unsealed circuit boards and open case air cooled motors over time..

Hope this helps.