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Old 23-07-2016, 08:50   #16
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Re: Use of hydraulics to better locate engine

Not only the heat issue, but if the hose breaks, you got one hell of a disaster to deal with, even perhaps a hole in the hull. At those pressures, you got a lot of stuff being exploded throughout the engine space. Steel may be strong but it bends and welds are funny.
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Old 23-07-2016, 08:53   #17
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Re: Use of hydraulics to better locate engine

There are no explosions to be worried about.
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Old 23-07-2016, 09:13   #18
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Re: Use of hydraulics to better locate engine

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Originally Posted by Velella99 View Post
Thank you very much for all your replies. I must admit to being a newbie on the cruising scene so apologies if this thread and subject has been done to death. I can see from your comments that the shift from mechanical to fluid to mechanical or mechanical to electrical to mechanical has an penalty of between 10 and 30% efficiency compared to your standard engine gearbox drive systems. Based on your comments that means that you've got to have a compensation larger engine and accordingly higher fuel consumption and fuel storage. I guess that puts paid to the idea so I thank you for your comments.

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Now, a hydraulic transmission is a thing of beauty: http://4.bp.blogspot.com/-tykIuU9u4Z...bay+130225.JPG

That said, it's a lot like the way an inverter works. As turning DC into AC is lossy as hell, so is your idea. If you had to do this, it would be better to go diesel-electric, but that wouldn't be my first choice either as it brings a lot of complications to a steel boat.
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Old 23-07-2016, 11:14   #19
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Re: Use of hydraulics to better locate engine

Yes there are some drawbacks BUT the versatility in my opinion is worth it The engine placement for trim and repairs I had one for years in a full keel 37 footer and I lost efficiency and the rest but to me the benefits far outweighed the draw backs
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Old 23-07-2016, 11:48   #20
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Re: Use of hydraulics to better locate engine

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There are no explosions to be worried about.
Oh yea of little experience. When a hydraulic line goes while under pressure(i.e. excavator pushing a major load), it ruptures with enough force to throw the hose line particles through tempered glass, retaining rings through steel meshed cages, and heated oil to blast leg muscles off a foreman who was standing nearby. Do not underestimate super heated oils under immense pressures.
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Old 23-07-2016, 12:07   #21
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Re: Use of hydraulics to better locate engine

Hi,
Scorpius is a Colvin Gazelle hull with custom deck and house, a conventional sloop/cutter rig and, accordingly, 6000 lbs of lead ballast.

Designed to be engineless, when I bought her she had a 10 hp diesel tucked into a locker under the port side deck. The prop emerged 3-4' off center. It was a disaster! You couldn't go, couldn't stop, and couldn't manoeuvre.

We repowered in 1987 with an Iszuzu C240 engine (48hp), a Cessna swash plate variable output hydraulic pump, and a 50 hp hydraulic motor mounted on a thrust bearing down in the box keel. We cut a propeller aperture in the back of the keel (easy to do with a steel boat) directly in front of the rudder and . . .

It works like a charm. In the 30 years I've had it I (including 4 years offshore) I've had to replace one seal and a couple of hoses.

It's fantastic for docking as I just set the throttle for 1500 rpm and play with the "gear shift" to put as much power to the prop as I need. I can also turn her in her own length by putting the rudder hard over and alternating between 3/4 power ahead, then astern "kicking" the stern sideways each time I go ahead then checking forward motion by going astern.

I burn one US gallon an hour at 1800 rpm - which I find quite acceptable.

I also have a hydraulic anchor winch with a Charlene motor powered by a separate hydraulic pump electrically clutched off the main engine. I've pulled up many an anchor for people whose electric system has either burned up or otherwise died.

I wouldn't have it any other way. (Hydraulic systems are BIG on commercial boats here in the Pacific Northwest and there's lots of expertise and support).
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Old 23-07-2016, 12:42   #22
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Re: Use of hydraulics to better locate engine

I used to drive OLD Smit Tugs around 150 foot, a couple were single screw with three Kromout engines. As I recall one swung a 12 foot wheel in a Kort nozzle. Lots of torque there.

It was DC though. BIG contactors, generator behind each engine and one electric motor on the shaft.

It worked ok, a bit of delay between an engine bell and response but that is normal with a telegraph system. We had direct “push button power selection” but it often failed so I used the telegraph.

No fun when maneuvering and we would knock it off line.. take the engineer a few moments to get us back on line and during that time the tow was free to do what she liked..not fun at all. It seemed complicated and complex. The Chief was always replacing contacts and relays.

To me direct drive through a gear is simple proven and works. I have had lots of hydraulic drive winches, captstans, cranes, bow thrusters etc and they all work fine, but constant hydraulic drive generates a lot of heat and can be very noisy.
Good ideas can be great ideas, but I have found on a boat, where things must be very reliable with short crew, simple and reliable works. And works and works.

Just my thoughts.

Michael
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Old 23-07-2016, 14:10   #23
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Re: Use of hydraulics to better locate engine

A question to all of the hydraulics naysayers: Have any of you ever had a sailboat equipped so? I have, a 22ft waterline sloop with which I crossed the Atlantic (Canada to Portugal), allowing me to speak from experience, to say that hydraulics are A-1. Please don't put such a fear into someone that they discontinue their search for something better.
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Old 23-07-2016, 14:12   #24
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Re: Use of hydraulics to better locate engine

Have had hydraulic propulsion ( 18 series pump and motor) for 16 years on a 35 foot, 7.5 ton sv, about 1/2 life of vessel. Did replace engine 10 years ago plus had hydraulics refreshed/rebuilt with new hosing and heat exchanger (cooling cct ruptured). There is a 10 percent efficiency loss to the prop however I have found that I have lots of power at optimum engine rpm (2200) 37.5 hp kubota to propell boat at hull speed 7kn in most conditions. I burn about 1.5 litres/hr or less. Prop is 16 x 12p 3 blade Campbell.
There is very little engine,pump noise but motor whine irrates at times. An advantage I think would be engine placement and no vibration from misalignment issues. In all I am quite pleased with the setup.
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Old 23-07-2016, 16:14   #25
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Re: Use of hydraulics to better locate engine

Have you thought of a couple of cv joints, they will be way cheaper and a lot easier to fix if a problem arises. Dont go and buy little car ones , we used Porsche 930 Turbo Joints which are from memory 100 mm with 25mm balls ,buy them through a bearing supply house , Not Porsche. They need to be of a recognised manufacturer USA GERMAN SWEEDISH!!!.
Thses joints a grease packed before you assemble and I would replace the boot clip with a stainless steel one if it isnt already SSteel. ACV joint of this size is by far overkill but the diffence in the price of small ones is not an issue. Servicing about once in 5 years, but they will last a very long time in this application.
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Old 23-07-2016, 17:08   #26
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Re: Use of hydraulics to better locate engine

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Originally Posted by Stumble View Post
It's actually worse than that. A generator needs to operate at a specific rpm to generate 50/60hz power. So the motor must be sized to generate X amount of power at that rpm, where a direct drive has a throttle and can match the rpm of the engine to the power demands.

So if you want a generator capable of putting out 35kw of power at 1800rpm, you need a monster power plant compared to a motor that can put out 5kw at 1000rpm, and 35kw at 4000rpm.

There is a lot of variables, but figure a generator with the same output needs to be at least double the physical size and weight as a direct drive.
No need for 50/60 Hz, or even for AC at all in this application...

Jim
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Old 24-07-2016, 10:11   #27
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Re: Use of hydraulics to better locate engine

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Oh yea of little experience. When a hydraulic line goes while under pressure(i.e. excavator pushing a major load), it ruptures with enough force to throw the hose line particles through tempered glass, retaining rings through steel meshed cages, and heated oil to blast leg muscles off a foreman who was standing nearby. Do not underestimate super heated oils under immense pressures.
Last time I looked we were talking sailboats My system operated between 700 1100 psi if heat is too much use a larger reservoir DUH!! And if 45 years in Aerospace is little experience well too bad Every time I offer advice on this Gong Show I flamed by a halfwit up your's I'm done
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Old 24-07-2016, 10:17   #28
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Re: Use of hydraulics to better locate engine

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flamed by a halfwit up your's I'm done
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Old 24-07-2016, 10:48   #29
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Re: Use of hydraulics to better locate engine

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No need for 50/60 Hz, or even for AC at all in this application...

Jim
That's true, and another thing is the gen engine, if it is making ac, can be running at 3600 rpm or so which is close to most engines highest HP or torque. So basically, maybe it could be the smallest possible engine for the KW required?
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Old 24-07-2016, 11:21   #30
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Re: Use of hydraulics to better locate engine

Again thank you all for your perspectives. None of this is wasted a I'm going to do some investigation based on leads you've given me above. The physics fascinates me and the options entice me. Thanks again.

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