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Old 30-07-2008, 08:29   #1
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Alternate propulsion

With the high fuel prices and the search for alternate sources to get from point A to point B, I have a question for the engineers on the board. Would it be possible from a practical and economical standpoint to build a propulsion system that is hydraulically driven with power for the hydraulics driven by a much smaller diesel engine then is typically found on most of our boats? For instance a hydraulic pump capable of turning the propeller at near the same RPMs as our current diesel and reversible to give us both forward and reverse thrust.
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Old 30-07-2008, 08:44   #2
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I was under the impression that the big gains for devices like electric and hydraulic would be the ability to swing a bigger prop at lower rpm, at which point you can reduce input power required. It would be a problem for most boats that weren't designed to fit a bigger prop. I don't think using the same prop at the same rpm changes the input power requirements much.

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Old 30-07-2008, 08:50   #3
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Lots can be done with prop size and pitch but I am more interested in the possibility of the system itself.
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Old 30-07-2008, 09:04   #4
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There has been much discussion about alternate forms of power here but it usually comes down to losses in power conversion eating up the possible gains in efficiency. There were some interesting articles about electric drive on Professional Boatbuilder site. We are close to having more efficient electric drives (more efficient than straight diesel drives). However new diesel engines are much more efficient than older units so the added expense may be less attractive. If you are thinking of replacing your 4-108 a new engine will probably be lighter, more powerful and more fuel efficient than what you have, without the added complexity of hydraulic or electric drive systems.
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Old 30-07-2008, 09:07   #5
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We are not thinking about replacing anything, just looking for theories at this point and consideration of something other than electric for which has been studied and discussed to great ends.
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Old 30-07-2008, 09:07   #6
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I'm no farmer, but don't a lot of tractors use hydraulic PTO's to spin the bush hog blade, run augers, etc.?
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Old 30-07-2008, 09:16   #7
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After I posted I remembered that you have a Yanmar, not a 4-108. Sorry.

And yes, hydraulic drives are used for many things, even on boats. But if you are considering the efficiency of your main drive system it probably is not the way to go. Every power conversion costs in terms of energy loss.
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Old 30-07-2008, 09:55   #8
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Chuck,
It's been done in a production boat. The Carter 30 in the 80's used a 10hp Farymann and a hydraulic drive. If you wanted to save fuel and cost. What about using the "alternative" propulsion you already have?
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Old 30-07-2008, 10:26   #9
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With the high fuel prices and the search for alternate sources to get from point A to point B, I have a question for the engineers on the board. Would it be possible from a practical and economical standpoint to build a propulsion system that is hydraulically driven with power for the hydraulics driven by a much smaller diesel engine then is typically found on most of our boats? For instance a hydraulic pump capable of turning the propeller at near the same RPMs as our current diesel and reversible to give us both forward and reverse thrust.
It sounds like you expect the hydraulic system to somehow magically "make" energy. Using a smaller engine will give you less power, always, period.

Hydraulics have advantages, mostly in fine speed control and the freedom to put the engine physically removed from the propshaft, but they are not more efficient than a standard transmission.

Retrofitting a boat to save fuel would not work.
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Old 30-07-2008, 12:21   #10
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Chuck,
It's been done in a production boat. The Carter 30 in the 80's used a 10hp Farymann and a hydraulic drive. If you wanted to save fuel and cost. What about using the "alternative" propulsion you already have?
That is a good point but I am thinking more along the lines of those times when the sails won't do, such as traveling the coastal waterways, etc. I did a lot of service work on Carvers for a dealer and was not aware of the hydraulic systems.
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Old 30-07-2008, 12:26   #11
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Agreed, any time power is converted there is some loss in the form of waste heat. It only makes sense to convert power if the reason for converting it is more important than the loss in efficiency. Hybrid boats that can get free energy from wind or solar used for short jaunts comes to mind. Its no big deal if you lose some energy that was free in the first place to heat loss from electric motors or to heat loss from charging a battery.

Also, hydraulic systems that convert mechanical into fluid energy and back are not 100% efficient. Larger hydraulic systems sometimes have coolers or rather large tanks that are used for dissipating the waste heat.

If you want hydraulic power for something else then it may make some sense. I have a couple hydraulic cable winches on the boat. Hydraulics makes perfect sense for this application because of the relatively low weight for the power of hydraulic motors and their weather resistance compared to electric motors. The regulation of a hydraulic motors speed is also much easier and simpler than an electric motor
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Old 30-07-2008, 13:16   #12
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The reason I had thought about hydraulics was to possibly include items such as the windlass, bow or stern thrusters, autopilot, dinghy davits and perhaps a few other onboard items.
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Old 30-07-2008, 13:22   #13
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That is a good point but I am thinking more along the lines of those times when the sails won't do, such as traveling the coastal waterways, etc. I did a lot of service work on Carvers for a dealer and was not aware of the hydraulic systems.
Not Carver, Carter like Our former President.
I also use hydraulics on the 70+ ft houseboats to power thrusters.

I just had to rib you a little about the sails.
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Old 30-07-2008, 13:29   #14
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Yeah the eyes are getting older I read Carver. We don't use these sails much anyway. On this last trip in the last two months we have sailed about 30 hours.
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Old 30-07-2008, 15:06   #15
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I've been looking into this as a pet project...

Haven't found many, but there are hydraulic motors that work as pumps, in either direction. (I thought they were all the same when starting out the search...)

Mainly thinking that hooking a big electric motor up to the hydraulic pump would allow it to be driven as a generator under sail. Or, run under diesel power only... or powered off the batteries as an electric generator.

Bonus would be if the thing could be an outboard of sorts, so when you only want to sail the prop could be lifted clear of the water...

Don't think it'd be cost effective, but might have a high "cool" factor.
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