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Old 02-07-2008, 04:13   #1
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Hydraulics vs Electrics.

I am in the final stages of having the electrics drafted for a 65' 45 tonne steel cruising monohull. Electrical designer suggests that all the sytems are electric given that I will have a very strong DC system with 800 AH batteries, twin inverters and two generators.

Survey standard specifies 16mm chain.
Most people I talk to suggest that the twin anchor windlasses (4500's) should be hydraulic at this size (200 lb anchor + 16mm chain). If this is to be so then I would use hydraulics for the 30HP bowthruster. Logically that would suggest a central hydraulic power pak running off genset and/or main motor. In which case does it not make sense go go the full monty and run the powered winches and furlers by hydraulics too rather than muck about with electric winches?

In summary:
Is hydraulics the preferred option for windlasses ?
If this is so, is it reasonable to run everything off hydraulics?

Would appreciate some real world input.

Richard
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Old 02-07-2008, 05:18   #2
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Why not just go up to 24 volt systems for the BT, windlass, and winches? I'm not a big fan of hyd systems on a sailboat, unless you want to run the generator all the time.
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Old 02-07-2008, 06:48   #3
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24 Volt

Is designed as 24 V system already. This makes sense for wiring and capacity of course, but did not think it made much difference to the windlass issue. Slightly easier to do 48V for an electric BT I guess.

Would have a 24 V hydraulic powerpak for small consumers like winches but would use main motor or genset for bigger demands.
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Old 02-07-2008, 08:38   #4
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If 24v isn't enough, then I'd seriously consider hydraulics. I'd maybe consider them from the start. We have friends with the same boat we have with a hydraulic bow thruster, windlass, and roller furlers - along with boom vang and backstays.
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Old 02-07-2008, 08:47   #5
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You should be all set then. We use almost all 24 volt systems for our boat and it is about the same size you are building. Harken 98's, Vetus bow thruster, ... all 24 volt. No problems.

61 foot, 65k disp, main 1,000 sq ft, genoa 1700 sq ft, kites ~3500 sq ft, not sure what else to add.

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Is designed as 24 V system already. This makes sense for wiring and capacity of course, but did not think it made much difference to the windlass issue. Slightly easier to do 48V for an electric BT I guess.

Would have a 24 V hydraulic powerpak for small consumers like winches but would use main motor or genset for bigger demands.
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Old 02-07-2008, 22:49   #6
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hydraulics vs electrics

In a very general way, hydraulics are preferred over electrical. All things being equal, the hydraulic systems tend to have higher torque, are more reliable, and more repairable. Iirc, they also tend to be more expensive, initially. If you completely revamp all the systems you can to hydraulic you'll probably improve the reliability of those systems.

Hydraulics depend, usually, on the main engines. (This also gives you a potential weak point, with only one power source.)

Personally, it sounds like you've already invested heavily in your electrical system. Stick with that, rather than adding another system to the boat.
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Old 02-07-2008, 23:21   #7
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Amgine stole my post. He is pretty much spot on. Hydraulics will offer the greatest longevity and reliability. But they are very expensive. Very very expensive and complex. Some very cool tricks can be down with hydraulics. One advantage is being able to set "load stall points". If something jams, the motor can have a relief system so as the motor doesn't wreck something. Flow controll can adjust speeds of winches etc. Hydraulics are very powerful, but can be made safe. Electrical is not so easy. You can protect a stalled motor with an overload, but you can not regulate a load so easily, like a jammed sail.
One concern I have is the Bow thruster. 30Hp is a lot of power electrically. Even 24V, you will need batteries near the thruster and some very heavy and short runs of cable. In fact I am surprised they do a 30Hp 24V thruster. Thats over 900A of current draw.
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Old 02-07-2008, 23:26   #8
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See, I see hydraulics as much simpler than electrical. They are just applications of mechanical force. Electricity is the weird scary stuff... <winks>
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Old 02-07-2008, 23:41   #9
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I have to agree with the statement made by wheels. "900 amps is a huge current draw, which will require short heavy cable runs with substantial batteries located very close to the load. It's like running 4 heavy duty starters at the same time. I personally like hydraulics and have not found them that expensive or hard to work with. Always good sources in the commercial fishing fleet communities. Very nice to control.
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Old 03-07-2008, 00:13   #10
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I also come from a commercial background (although am quite a few years younger than some others here ).

I second their positive point about the use of hydraulics's. So long as you have most of your runs in SS piping & plenty of spare hoses, valve controls, thread & denso tape - then you should be OK.

IIRC, the power loss of hydraulics's (be it from a pto or direct driven) is about 10%.

Replacing parts is straight forward, just remember to disengage the pump & have a small bucket handy (for a minor amount of oil in the hose).
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Old 03-07-2008, 02:36   #11
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The depends and depends greatly. Power loss can be as much as 50%. It is the most uneconomic use or transition of energy, but it's advantages in many applications far out weight the ineficiency.
If a system is new and built properly, especially for a marine situation, Hydraulic can be kept very clean. These systems are not as heavily worked as in a fishing environment and the result is that they tend to last much longer and remain much cleaner. Down points are noise. The pumps make quite a whine. They can be sound proofed in an engine room though. The pumps can also be brought on and off line by electric clutches, so noise can be reduced to when the pump is in demand. Also if the pump is running, it is taking power from the engine. Whether a winch is running or not. The greater load is when the winch is doing most of the work, but there is still a load when nothing else is running.
Another point to consider is the weight. Hydraulic motors are nuggity wee things. But can produce incredible power for their size. But an issue on a sheet winch would be getting the hoses to the motor. They are stiff and heavy and the connections are quite bulky.
My though would be electric sheet winches. Hydraulic thruster and anchor winch. That way you can use those when the main engine is running anyway. You could switch in and out the pump if you wanted to run the engine for say charging and not have fuel being used to run a pump not being used. I find it hard to believe a thruster that is 30Hp is available as electric. Wow.
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Old 03-07-2008, 03:11   #12
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Quote:
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loss can be as much as 50%.
OK, I'll give you that point

Quote:
I find it hard to believe a thruster that is 30Hp is available as electric. Wow.
I've seen on bigger boats - some of them run an AC line just prior to the thruster then convert it to DC.
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Old 03-07-2008, 03:19   #13
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I'd second that
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Old 03-07-2008, 04:39   #14
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Thanks for the response - much appreciated. Sounds like life generally - some good, some bad either way. Might compromise and go with hydraulics for the big consumers and electrics for the winches.
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Old 03-07-2008, 05:50   #15
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We run a Vetus 220 at 24v with a current draw of 760 amp held in check by a slow blow 500 amp fuse. The batteries are midship and the unit is powered from cable runs to the bow thruster (~35 feet?). One thing to remember is that the current draw is intermintant and the batteries are being charged since the propulsion engine is running and turning the 24 v alternator.

But, whatever works for you.

Cheers,

Joli
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