How come we don't see hydraulic outboards?

Discussion in 'DIY Marinizing' started by parkland, Feb 11, 2013.

  1. mike Banks
    Joined: Oct 2013
    Posts: 11
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Australia

    mike Banks Junior Member

    Hydraulic outboards.

    We do see them. An outboard leg powered by a hydraulic motor driven by an engine powered remote pump works well. Most are monstrous big things used on commercial barges and the like--but I have seen outboard motors converted to the task and these work OK.
     
    Last edited: Oct 30, 2013
  2. powerabout
    Joined: Nov 2007
    Posts: 2,901
    Likes: 61, Points: 48, Legacy Rep: 719
    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    There is IMO approved stern tube oil and thats all you are allowed to use
     
  3. SamSam
    Joined: Feb 2005
    Posts: 3,817
    Likes: 153, Points: 63, Legacy Rep: 971
    Location: Coastal Georgia

    SamSam Senior Member

    .


    These are apparently used in narrowboats, which are a reasonably size boat.

    http://www.betamarine.co.uk/inland/Beta_Hydraulic/hydraulic_propulsion.html

    [​IMG]


    (The above is from this thread... http://www.boatdesign.net/forums/diesel-engines/hydraulic-propulsion-generator-49213.html#post669298 )


    .
     
  4. discovery
    Joined: Aug 2013
    Posts: 78
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Australia

    discovery Junior Member

    Another thing to think about, high pressure hydraulic oil is every bit as dangerous as high voltage electricity, but there are no-where near as many laws and codes of practice controlling who works on and repairs it as electricity has.

    Another point is that hydraulic drive systems in general don't get efficient until pressures start climbing sky high. Most of the barges and such I have seen use the hydraulics for other purposes, and the propulsion is only a secondary requirement, but because its already there, relatively easy to set up. I have seen an alternator run hydraulically for lighting and welding on one barge that was repairing marina pylons. It also had high pressure water pumps, low pressure high volume water pumps, 2 cranes, 2 winches, air compressor and even air con in the donga, all run hydraulically.
     
  5. parkland
    Joined: Jul 2012
    Posts: 700
    Likes: 6, Points: 18, Legacy Rep: 40
    Location: canada

    parkland Senior Member

    I was just thinking today,

    While hydraulic systems might not be as efficient as gear box drives, they might end up being more efficient if the system allows the use of a better engine because of placement.

    Consider a retro-fit where the boat had outboards, and where an inboard engine would go is used for living space, replacing outboards with a diesel engine mounted anywhere might be better.

    Also a hydraulic outboard could mount to the front and be lifted out of the water underway, to add extra maneuverability.

    What about synthetic hydraulic oils? Surely there must be ways to get better use of power....
     
  6. powerabout
    Joined: Nov 2007
    Posts: 2,901
    Likes: 61, Points: 48, Legacy Rep: 719
    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    hydraulics are also very noisy as in more than any other drive system
     
  7. discovery
    Joined: Aug 2013
    Posts: 78
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Australia

    discovery Junior Member

    Just 1 of the reasons hydraulic drives are not as efficient is because you have changed the way the power is being used and every time you do this you lose some of the power. If you start with the fuel as chemical energy, we turn it into mechanical energy inside the engine, we are familiar with the losses here. We take it from the engine as mechanical energy, modify it in the marine gear, and put it to work pushing water at the prop.
    If we then add another step and turn the mechanical energy into pressure with ah hydraulic pump, and then turn that pressure energy back to mechanical energy with a hydraulic motor, and use the hyd motor to push water with a prop, we've added 2 extra steps into the equation, and these have to come at a cost in energy, which increases the efficiency losses.

    To have a outboard over the front is basically re-inventing the wheel , the wheel being a drop down bow thruster, and these are already available in hyd and electric drive.

    There has been a lot of study with hydraulics in using water instead of oils in environmentally sensitive areas. As yet though I am unaware of any successful reliable systems. Atlas Copco were one of the main pushers in this area with their rockdrills.
     
  8. powerabout
    Joined: Nov 2007
    Posts: 2,901
    Likes: 61, Points: 48, Legacy Rep: 719
    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    Afaik all drilling vessels are using some water based hydraulic oil.
    We certainly are on board where I am
     
  9. parkland
    Joined: Jul 2012
    Posts: 700
    Likes: 6, Points: 18, Legacy Rep: 40
    Location: canada

    parkland Senior Member

    Water based oil ? :)
     
  10. powerabout
    Joined: Nov 2007
    Posts: 2,901
    Likes: 61, Points: 48, Legacy Rep: 719
    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    I assume its synthetic but dissolves in water.
    You can get it as coolant for your engine as well
     
  11. black_sails
    Joined: May 2016
    Posts: 33
    Likes: 1, Points: 6, Legacy Rep: 10
    Location: Minnesota

    black_sails Junior Member

    Hi, I realize i'm two years late to the party but since I joined just to mine the years old knowledgebase and even hope to continue some old conversations (even if with totally different people than who originally started them) i'm trying to contribute where I can, and I didn't see anyone provide a specific figure yet.

    I think the efficiency of a hydraulic drive on a smaller system struggles to even hit 80%. That someone else mentioned trying to reach 85% and failing on 1000hp sounds about right - smaller systems can be even worse even 65% I think. I don't have a reference handy for this factoid but I remember reading it when trying to research creating a hydraulic hybrid car wanting to improve efficiency and was talked out of it after I found out about the 20% loss factor. If a hydraulic engineer ever stops by they can correct me but i'm fairly certain on that number because it's the single number that made me poopcan the hydraulic hybrid project when I stumbled across it.

    If you look at the Brake Specific Fuel Consumption map of any set of diesels they always have an 'island' of ideal efficiency which in many cases might be say 206g/kwh at the center, drifting towards something like 220g/kwh over a fairly wide range to either side, only running grossly out of spec (redline RPM, idle RPM, unusually low loads) that you'd never cruise at might you see a 20% difference in additional fuel usage efficiency so the gearing advantage on the same engine is unlikely to do any good and any mechanical transmission would be a better way to correct it.

    I also don't believe you will see a 20% more efficient engine at anywhere close to the same usable powerband/you would struggle to even break even with the original direct mechanical link. Again a mechanical transmission would make more sense to make up the difference.


    In short it could be done, and yes would have those cool benefits you listed plus the detriments others have listed, but doing it for the sake of efficiency would probably not be one of them.
     

  12. aussietrev
    Joined: Jul 2006
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: australia

    aussietrev Junior Member

    The rockdrills were actually using water in the examples I saw with an industrial bean pump making pressure.

    The key to efficiency with hydraulics is pressure, some of the largest excavators using up to 3500 and 4500 psi to do the work. Low pressure hydraulics generally do not equate to efficient systems. The problem with these sorts of pressures is transmitting it, hosing and connections being the big issue in a (usually less than ideal) environment . At these pressures, a pinhole will cut through pretty much anything it wants short of steel which becomes dangerous in the vicinity of persons trying to enjoy an outing.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.