Why Not Use AC Power for Thrusters and Windlasses?

[Cadence]

Originally Posted by Dockhead

Fantasizing about having a new boat built, I was thinking about the best way to drive the thruster and windlass.

My boat uses 24v DC power for this, which works fine with a large battery bank and large alternator.

Hydraulic would be better of course, but expensive and awfully messy (!) if you have a leak.

So why not use 230 volt AC power instead? I believe Lofrans can make their windlasses to work with this. Getting a few kilowatts of power to the device at 230v is trivial, compared to doing it at 24v, and I believe that AC motors are more efficient, too. My thruster is 10 horsepower or less than 7kW. At 230v, that's less than 30 amps, compared to hundreds of amps of DC power.

In the past, cruising boats didn't usually have that much AC power on board, but these days we have inverters which could power such devices, with AC generators for backup.

What would be the downside to this? Seems ideal for a boat with robust AC power system, which more and more larger cruising boats now have.

I can see AC for a thruster app. but if memory serves me AC does not have the initial toque of DC.

[zboss]

I think thats a great idea. We don't have a thruster but our windlass is only 130 amps @ 12 volts... inrush current is closer to 200 amps but still that is only 2400 watts.

at 240 volts we could get away with a 12 AWG wire which is a significant drop in weight from the 0/2 wire we currently have. Also, we could ditch the solenoid and use direct switches.

[exMaggieDrum]

Hydraulic systems do not have to leak. It does happen but not always by any shot.

[jldunn86]

Originally Posted by poiu

Hydraulics is fine too. Messy like you say when (not if) it leaks. If you had a thruster powered off the main engine hydraulic pump and fitted a pump to the genset as a back up you could have a redundant system with similar weight and power to the DC system, but with a bit of extra redundancy ie can work with a house battery failure. Still, that said, I don't think redundancy for the bow thruster is too important as you have your redundancy in the form of a dinghy and when you are using the bowthruster you are often in a marina where there are usually marina staff or other boaters to help.

Lets not forget the independent hydraulic power packs, both diesel and DC or AC electric. Redundantly speaking.

[s/v michaela]

My reason for not using the hydraulic thruster was the fact that with a large thruster the 6-71 would have to be really revved to supply enough power.At the same time it would be more difficult to control the fore and aft motion of the yacht with the transmission if the engine was revved up.

[Colin A]

I've seen quite a few on commercial boat projects we have done. As well as on newer Navy projects. But most are 3 phase with VFD's. I have seen a few single phase application in specs and drawings but haven't seen one in real life. I have noticed more and more AC power for items like these on boats over 75' and less hydraulic so that may be the way things are going. Of course many of these boats also have a main and a backup Gen as well so there isn't much concern about backups. The also run the Gens constantly so the power is almost always there.

[Krilleonnova]

you all talk like if AC power is simple
AC power from two or more sources simultanisly is difficult

the phase must be syncronized or you can burn out everything

is an inverter normally built so that it syncronizes its output with the
generators output? What when you use several small inverters?
DC is simpler you can add as many sources as you like as long as the voltage approx the same.

[Cadence]

Originally Posted by Colin A

I've seen quite a few on commercial boat projects we have done. As well as on newer Navy projects. But most are 3 phase with VFD's. I have seen a few single phase application in specs and drawings but haven't seen one in real life. I have noticed more and more AC power for items like these on boats over 75' and less hydraulic so that may be the way things are going. Of course many of these boats also have a main and a backup Gen as well so there isn't much concern about backups. The also run the Gens constantly so the power is almost always there.

You have that right. Having worked a tug the gen, (I being a lowly oiler) I fired up before the main and shut down last.

Most pleasure craft don't. Ari's probably did.

[Cottontop]

Originally Posted by kas_1611

Am I missing something here but why?

I don't know about anyone else but we have the engine running when we need to use the thrusters or the windlass so have plenty of DC amps on tap. We run on 12v and have 135amp in the house battery (windlass) and around the same for the thrusters (can't check as they are under the bed and junk cupboard).

So I guess my question is why go to all the hassle of having to fire up a generator or plumb in inverters etc to go AC when your alternator will already be spinning and providing plenty of juice to power either or both?

KISS springs instantly to mind

Keiron

Well, 12x135 is about 1.5kw. Dockhead is looking for 7-8kw.

[Cadence]

Originally Posted by kas_1611

Am I missing something here but why?

I don't know about anyone else but we have the engine running when we need to use the thrusters or the windlass so have plenty of DC amps on tap. We run on 12v and have 135amp in the house battery (windlass) and around the same for the thrusters (can't check as they are under the bed and junk cupboard).

So I guess my question is why go to all the hassle of having to fire up a generator or plumb in inverters etc to go AC when your alternator will already be spinning and providing plenty of juice to power either or both?

KISS springs instantly to mind

Keiron

[Cadence]

Originally Posted by Krilleonnova

you all talk like if AC power is simple
AC power from two or more sources simultanisly is difficult

the phase must be syncronized or you can burn out everything

is an inverter normally built so that it syncronizes its output with the
generators output? What when you use several small inverters?
DC is simpler you can add as many sources as you like as long as the voltage approx the same.

Your correct I guess old school. Some gen sets and inverters sync. today like the small Hondas. I got corrected on that warning about the same thing. It seems like a whole new technology producing 60cps/Hz from a high frequency and someone posted the clean sine wave. You and I guess use CPS? Still probably a good warning for most.

[mitiempo]

To produce 30 amps AC will require, with associated losses, 300 amps DC. I see no advantage.

[Jon Eisberg]

Originally Posted by Krilleonnova

you all talk like if AC power is simple
AC power from two or more sources simultanisly is difficult

the phase must be syncronized or you can burn out everything

is an inverter normally built so that it syncronizes its output with the
generators output? What when you use several small inverters?
DC is simpler you can add as many sources as you like as long as the voltage approx the same.

Originally Posted by kas_1611

Am I missing something here but why?

I don't know about anyone else but we have the engine running when we need to use the thrusters or the windlass so have plenty of DC amps on tap. We run on 12v and have 135amp in the house battery (windlass) and around the same for the thrusters (can't check as they are under the bed and junk cupboard).

So I guess my question is why go to all the hassle of having to fire up a generator or plumb in inverters etc to go AC when your alternator will already be spinning and providing plenty of juice to power either or both?

KISS springs instantly to mind

Keiron

Originally Posted by poiu

AC shock hazard in a wet area like the anchor locker or ugh, the bow thruster locker fills me with dread.

The above are the words of wisdom in this thread, to me... ;-)

Originally Posted by Dockhead

You've spent time on my boat -- you've no doubt noticed the seamlessness between AC and DC power -- there's always AC on tap no matter what, and no one ever worries about power (until the batts start to run down after 24 hours of sailing ). I'd like for the new boat to be like that, too, even more so.

Hmmm, I've never seen such a boat, myself... If indeed yours is an example of one, perhaps you should just keep it... ;-)

I've run a few where this level of (needless) complexity underlies the approach towards the systems aboard... In my experience, virtually guaranteed to ensure heartache (or even worse), eventually...

;-)

[Cottontop]

Originally Posted by mitiempo

To produce 30 amps AC will require, with associated losses, 300 amps DC. I see no advantage.

One advantage is minimizing the amount of the heavy and difficult to work with DC cables necessary for those 300 amps.

[Starblossom]

I have used an IDEAL windlass powered by an AC motor for 32 years on a 62' monohull with no problems.

The generator has never quit by the demand for power and no unusual noises have never emanated from the engine room.
the gear box has been rebuilt once and the motor 2 times.

Ideal has friendly customer service and a pleasure to do business with.