12V vs 120V

[sailingharry]

So a thought crossed my mind. Many cruising boats have ample electric, including robust inverters. Inverters, at least good ones, are highly efficient, and have incredible reliability records -- my father cruises extensively with a nearly 20 year old Xantrex, I just looked at a 20+ year old boat with its factory installed Heart 2.5KW. So why aren't we taking advantage of this power for high amp loads?

For instance, a windlass. A Lewmar V2 draws 80 amps. You can handle this with a second battery setup, with maintenance, replacement, echo charger, etc. Or you can run 2/0 cable (assuming 30' each way, that gives you 3.2% drop) at a cost of over $300 plus fittings, fuse blocks, etc. Or, you could build it as a 120V unit, with about 8A current draw. Then, a #14 wire would give you a 1% drop, at a trivial cost, with standard panel circuit breakers, and a vastly easier installation.

Or, try a bow thruster. A Vetus 60 draws 280A. Wow. Without considering voltage drop, you need a 1/0. 4/0 would give you 7% drop at 30 feet, probably acceptable for a thruster -- at a cost of $600 in cable. But at 120V, the current is only around 28A and you could run it 30' away with a #12 at 2.3% drop. It would take an inverter rated for 3.5KW surge (thrusters are rarely run for more than 10 seconds at a time).

Or even a big washdown pump. The big ones are 20+ amps at 12V, but would be only 2A at 120V. For 12V, #6 would get you to 4% drop -- for 120V, you'd be fine with the smallest wire you'd be comfortable with (for physical endurance reasons, I rarely go smaller than #14 for any circuit except signal stuff).

Yes, electrical safety would need to be addressed. But all these items use relay control circuits anyway, which could remain 12V.

None of these items are "critical safety items" (yes, to some degree -- but not the same category as engines, or bilge pumps, or navigation lights, or other such gear), they are usually used with the engine running, and since the use is very short duration, the inverter would not need to be left running 24/7 (although is suspect many are). Use of 120V would dramatically improve installation labor/cost, and since the motors have smaller windings the units themselves should be cheaper and maybe even smaller. And since the current handling is MUCH smaller, it could significantly improve reliability/safety.

What am I missing? Why is this not normal?

[TreblePlink]

Even efficient inverters have loss. As a rule of thumb: always use native boat battery system voltage unless there is no other way than to convert. This is particularly true with 12 volt boats.

If you are needing big power, consider a small generator.

[atoll]

no reason why not to apart from,watertight integrity of 120v/220v equipment available for marine applications,and risk of fatal electric shock.

also you need a reliable a/c supply from either a generator or inverte with suffcient battery storager,or both.

KISS

[sailingharry]

Originally Posted by TreblePlink

Even efficient inverters have loss. As a rule of thumb: always use native boat battery system voltage unless there is no other way than to convert. This is particularly true with 12 volt boats.

If you are needing big power, consider a small generator.

Indeed, many boats also have generators, making the question even more relevant.

As far as loss, they are around 95% efficient. Even so, when you are talking about huge, intermittent loads like windlasses and bow thrusters, your engine is probably running and you aren't very worried about power consumption.

[sailingharry]

Originally Posted by atoll

no reason why not to apart from,watertight integrity of 120v/220v equipment available for marine applications,and risk of fatal electric shock.

also you need a reliable a/c supply from either a generator or inverte with suffcient battery storager,or both.

KISS

Availability is surely a challenge -- hence the question. Although at least one windlass company (Quick) makes a 120V, and one would "assume" that they make it fit for marine use.

For these loads, you need reliable and large power supplies, regardless of 120 or 12V. And yes, you would need reliable 120V -- but many cruising boats these days have robust inverters and/or generators to provide reliable and substantial 120V. Hence the question.

[atoll]

Originally Posted by sailingharry

Availability is surely a challenge -- hence the question. Although at least one windlass company (Quick) makes a 120V, and one would "assume" that they make it fit for marine use.

For these loads, you need reliable and large power supplies, regardless of 120 or 12V. And yes, you would need reliable 120V -- but many cruising boats these days have robust inverters and/or generators to provide reliable and substantial 120V. Hence the question.

my anchor windlass is 240v and works well,but the switch gear in order to reverse the 2kv motor cost more than the motor and gearbox that was adapted as an anchor winch.so i am not sure how much of a gain financially it would be . itis very reliable,but does require the genset running to haul the 100lb anchor,plus has no manual override if you needed to lift by hand

any moisture in either the motor, controller,wiring or switchgear would cause it to trip,which with a dc unit would not be as much as an issue if it got wet