hydraulic propulsion for tugboats??

Discussion in 'Propulsion' started by tugboat, Nov 19, 2010.

  1. tugboat

    tugboat Previous Member

  2. tugboat

    tugboat Previous Member

    Would I mount the thrust bearings close to the gears/pulleys? or would they be mounted close to the stuffing box? much appreciated again..this is a very helpful thread for me..
  3. Lurvio
    Joined: Jul 2009
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    Lurvio Mad scientist

    The chain system is a good alternative to gearbox, and a lot cheaper. Hydraulic motor working on right rpm in the first place would be simpler and more reliable.

    Here's a schematic of the hydraulic part I sketched. The pros can probably find something wrong about it, but it's here to give an idea.

    On the left side, bi-directional variable displacement pump, center has a fill/recycle valve, right side has a bi-directional fixed displacement motor and at the bottom oil reservoir. The extra line from the motor is the leak return.

    The fill/recycle valve is needed to fill the loop and to cycle the fluid to the reservoir and/or oil cooler. The valve is pressure controlled and works automatically.

    The user controls basically two things, motor throttle (rpm) and pump plate angle (in this case for example 45/-30 or 45/-45 deg. axial piston pump). Both can be controlled in a number of ways.

    For the symbols, this is a good list.

    Example of a pump, this unit can be installed one after the other, so no need for gearbox there, just a bellhousing.
    Bosch Rexroth Pumps

    And this might work as a motor, at least the torques are massive.
    Bosch Rexroth Motors

    Food for thought. :)

    Last edited: Nov 23, 2010
    1 person likes this.
  4. tugboat

    tugboat Previous Member

    Lurvio--thanks for going to all that trouble in making such a great diagram...
    Do you mind if i post this on another thread??..we are talking about this exact thing--whether hydraulics are powerful enough--seems the larger bosch hydrualics would be pretty powerful--if im not mistaken they give KW's for the engines?...then i can convert to hp - constant is .7645 x Kws???
    cant rememebr the exact figure...ill go look on internet
  5. Pierre R
    Joined: May 2007
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    Pierre R Senior Member

    Tugboat it seems every time you turn around you want to take the tonsils out through the *** hole instead of the mouth. Why?

    If you want maneuverability why don't you play around with flanking rudders isntead of all this other BS.
  6. tugboat

    tugboat Previous Member

    Pierre r, im just investiging this at the moment..i have some time before I have to install anything as far as a motor. Flanking rudders are actualyl fairly complex..i did look into them too. but i guess i just still like twin screws. I know its more complex than a single...just want to get an idea of the viability of hydraulics...I love my big Caterpillar--but crap it burns fuel!..twin engiens would be a comprimise...
  7. Lurvio
    Joined: Jul 2009
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    Lurvio Mad scientist

    You can post it elsewhere, just add my name there somewhere. :)

    I have a habit of trying to learn new things and you presented a good opportunity for just that.

    To my understanding hydraulics would be the second simplest propulsion system right after straight shaft. But of course there are some losses, someone else have to tell you how much. These things are used day in, day out around the world in all sorts of machinery applications, so their ruggedness should be well proven.

    I can not claim it's the best system for your boat, but at least deserves some more thought.

  8. TeddyDiver
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    TeddyDiver Gollywobbler

    You can expect some 60% effiency with open circuit and 80% with closed circuit hydraulics. That is if the setup is optimized for the task..
  9. tugboat

    tugboat Previous Member

    TeddyDiver--what siz e motors would i need--??..i looked at Lurvios site. but still have a hard time figuring out what calcs to use to find the right size engine...i have two possible props..twins 24 x 25 or twins 20 x 19...
    thanks for the post!
  10. tugboat

    tugboat Previous Member

    Lurvio--Im learning as much or more than you! Ill make sure you get full credit for the diagrams..ill post them on "did a dream got shattered" on this site..
  11. Lurvio
    Joined: Jul 2009
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    Lurvio Mad scientist

    I think you have to know how much torque the prop needs at top rpm and select the motor according to that (one size bigger for longer life), look up the amount of oil flow needed and select the pump to suit. Then check if your diesel can keep up and start over if it doesn't. :p

    I'll go check that thread also, been a while since I did that.

    Thanks Teddy for the numbers.

  12. sbmar.com
    Joined: Nov 2010
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    sbmar.com Junior Member

    Hydraulic Drives


    I've attached a small piece (.pdf attachment) I put together on my experiences with hydraulic drives.. Since we do a lot of hydraulic work for fishing boats, driving a prop was fairly easy to sort out compared to some of the pressure compensated multiple drive systems we put together for commercial fishing boats...

    Anyway, hope you can glean something that may help you say yea or nay to a hydraulically driven prop..


    Attached Files:

    2 people like this.
  13. tugboat

    tugboat Previous Member

    Thanks Tony- one problem which we were having ahuge discussion over at BErts thread(did a dream got shattered) was that the hydraulics were producing only about 2 hp. this seems odd to me but thats what the calcs tell us..please read the last 3 pages of that thread and youll see what i mean--we did all the calcs- but for me somethings not right--i dont know how an excavator can operate with engines of 2 hp?? one of the engines porduced 2 hp at 300 psi flow and 20 gph but had 2630 ft-lbs torqu!! how is this possible?...very kind for posting..thanks--ill read it over and get back to you...
  14. Lurvio
    Joined: Jul 2009
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    Lurvio Mad scientist

    Thank You Tony for the pdf. That is as relevant information as it gets. And good pictures of the installations too.


    Your 2hp problem is result of too small components, you need more oil flow to transport more power. I had that hunch when I first looked the components over and the calculations (above and in the other thread) confirmed it. I do not remember seeing spec for your props other than the dimensions, so how much power does that prop of yours need? As far as I understand hydraulics, that really is the deciding factor in the setup. It dictates the pump size as well as the plumbing etc.

    If you want to get good info on your setup, info that can really be used to make decisions on, you should gather your information and e-mail it to a couple of the component makers or their local dealers.

    The list as I see it:

    - Engine spec (power, torque, max rpm, target rpm)
    - Props needs (how much power/torque it needs to turn at max rpm)
    - Description of the intended use, environment etc.
    - Something else? (guys help out here)

    Tony's approach above was an open loop system which worked for those boats and being simple are very easy to troubleshoot. But for a setup of this scale I would not even consider anything else than a closed loop system, something like my earlier sketch. In closed loop you only move oil when you need something to happen. For example an axial piston pump at zero plate angle has basically no friction (remember - this system does not have pressure on idle, the pressure only builds when the prop needs power).

    The fill/recycle valve is bit of an unknown as I did not found one on the BoschRexroth site (I didn't look all that carefully). The valve is structurally very simple, I can make one myself given proper tools so it should not be that hard to find. Should be not bigger than a 4'' by 4'' by 8'' block of Alu or Steel (cast iron maybe) with six connections. The flow rate needed for your power transfer will dictate the duct sized inside the block, I'd think it's going to end up being something between one and two inches.

    And finally again I have to say I'm not an engineer so the information given in this post (and many others) may be flawed. I have grown around farm machinery and know a fair bit of forest and construction machinery also, so I have a general understanding of how hydraulics work.

    Well, that's all folks, for a while.

  15. tugboat

    tugboat Previous Member

    Tony--very much appreciated!! i read through the article...I think that im going to shut the door on hydraulics. It seemed novel at first but it is more complex and requires machining and too many calcs that are uncertain for me. I dont know enough about hydraulics(yet). thanks for the help
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