Why Not Use AC Power for Thrusters and Windlasses?

[FamilyVan]

That sounds like a sweet windlass system Blossom.

I can almost guarantee running a thruster directly off a small genset would bark like a dog on the hunt though.

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[Dockhead]

Originally Posted by Jon Eisberg

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




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...

;-)

Systems design -- there's fragile complexity (my davits :headbang, then there's robust and redundant system architecture - two very different things which should not be confused.

Use AC power for as many things as possible (e.g. get rid of gas), then make AC power as robust as possible. An excellent approach for larger vessels.

I have a 2,5kw school bus alternator on the main engine, a 6.5kw heavy duty, prime power rated, low speed (1500rpm) generator. And a Victron charger/inverter bridging 230v AC and 24v DC systems. A Honda suitcase gen in the laz just in case. Abundant AC power comes from redundant, reliable sources. In the rare case of a generator problem, the alternator and inverter take over seamlessly. In case of weak shore power supply, the inverter will limit current taken from it and invert battery power to make up any deficit. It works great - no heartache at all. The only weak point is the charger/inverter - a crucial element and single point of failure. Solution is ganged redundant units, which is what I will do on the next boat.

My father's boat, prior to installing solar, was KISS - standard Perkins 12v alternator weakly charging a couple of 8Ds. No AC power except from small inverter plugged into a cig lighter socket. It was crap. Never enough power, even for lighting. Always worrying about it. Watching the battery monitor all the time. Running the engine for hours at anchor. Worrying about power for the pilot on passage. FFS, he even made me use the foot pump in the galley to save power on the fresh water pump! Bleh! You can have your KISS power systems - I'll take abundant power any day.

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[Dockhead]

Originally Posted by mitiempo

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

You lose more power in the first meter of DC cabling, than in the DC/AC conversion. Plus AC motors are more efficient. There are certainly big advantages. Whether that's worth the disadvantages, though, I dont know yet.

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[Colin A]

I've been told you need about 1kw per hp to start an electric motor with minimal sag. Not sure how true that is but lets say it is. Than a 10kw gen would be fine and in the size boat were talking about 11 and 12 kw generators are becoming common at least on motor yachts I've seen over 20kw on a 55 before. So the gen could handle it well at least as long as you shut off the A/C I would think the inverters could as well as a backup but you would be pushing them. It could make sense but really only on larger boats. A modern 65 is already so complicated having an AC powered bow thruster would likely be considered a simplification.

[Cadence]

Just a suggestion. Anyone advocating AC should Google Ward Leonard.

[Jon Eisberg]

Originally Posted by Cadence

Just a suggestion. Anyone advocating AC should Google Ward Leonard.

Duh, my money would have been on a search result that linked to the obituary of some guy who was electrocuted after stepping on his windlass foot switch....

;-)

[Jon Eisberg]

Originally Posted by Colin A

A modern 65 is already so complicated having an AC powered bow thruster would likely be considered a simplification.

Actually, that's a pretty good point, I suppose... ;-)

Originally Posted by Dockhead

My father's boat, prior to installing solar, was KISS - standard Perkins 12v alternator weakly charging a couple of 8Ds. No AC power except from small inverter plugged into a cig lighter socket. It was crap. Never enough power, even for lighting. Always worrying about it. Watching the battery monitor all the time. Running the engine for hours at anchor. Worrying about power for the pilot on passage. FFS, he even made me use the foot pump in the galley to save power on the fresh water pump! Bleh! You can have your KISS power systems - I'll take abundant power any day.

Well, I don't think anyone is suggesting you revert to Full Luddite Mode, many folks out there have managed to find a pretty acceptable middle ground...

It's just that having to fire up a generator every time you want to raise anchor, or come into a dock, seems like a bit of a head-scratcher, to me...

Just curious, what size do you figure The Next Boat is gonna be?

[Cadence]

Originally Posted by Jon Eisberg

Duh, my money would have been on a search result that linked to the obituary of some guy who was electrocuted after stepping on his windlass foot switch....

;-)

I'm not sure I follow that? I'm guessing you don't want to step on 220 AC, me neither. My point was DC allows control. I'm not advocating a Ward Leonard onboard, just the ability of control using DC vs. AC.

[Jon Eisberg]

Originally Posted by Cadence

I'm not sure I follow that? I'm guessing you don't want to step on 220 AC, me neither. My point was DC allows control. I'm not advocating a Ward Leonard onboard, just the ability of control using DC vs. AC.

Nah, I had no clue who Ward Leonard was, just an attempt at a bit of levity...

Wide of the mark, apparently...

;-)

[FamilyVan]

I think its a sweet idea. It could never work for me, because I could never afford to maintain such a complex system, I'm lucky to pay my moorage at a club that's about three levels above my social standing, as a result my boat is pure Luddite. Kerosene lighting, I have to put a bar on my windlass every time I want to use my anchor but I've always thought sailboats with systems like the Enterprise (Picards, not the USN one) would be a lot of fun.
I just started using a chartplotter (on my phone) and an AIS receiver after years of eyeballing and it has made me really appreciate cool gadgets.

Initially I was skeptical of your idea, but if you research it and have it properly designed you might be at the leading edge of a trend.

Good luck!

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[Cadence]

Originally Posted by Jon Eisberg

Nah, I had no clue who Ward Leonard was, just an attempt at a bit of levity...

Wide of the mark, apparently...

;-)

I may be dense and didn't catch the levity.

[chris95040]

Does using an AC motor complicate changing the thruster's output direction?

I imagine in the case of DC, you have relays or something reversing the voltage applied to a dc motor.

Maybe in the case of AC you'd need a gearbox? Or two distinct sets of coils?

Seems like the right idea though, moving lots of power around at 12, or even 24V, is madness...

[FamilyVan]

Okay, so a little off topic, actually, completely off topic, but this morning I promised to look for a photo of the AC thruster system that was installed on a tour boat I used to skipper. I couldn't find any pics of the thruster install, but I found a bunch of cool pics of the lengthening process, so I figured I would attach one.

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[minaret]

I think you should get a barn and some plans and have me come over and build a hull for you.

[buzzstar]

Most of the suggestions are OK, but a trans-oceanic extension cord would also do the trick with less fuss. I suggest using your native 24v DC for both. A windlass and a thruster are available with highly efficient motors in that voltage, and I truly doubt they'd be used often enough to drain or impair your system. Furthermore, in almost all circumstances where either would be used your engine is running and the alternator is replacing much if not all of the draw.