Electric or Hydraulic propulsion system for small boats

Discussion in 'Hybrid' started by jedclampit, Feb 26, 2006.

  1. jedclampit
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    jedclampit Junior Asparagus

    Hey all,

    Has anyone seen or heard of such a propulsion system for small boats?

    I have this concept for the propulsion of a sailboat based on the current technology utilized on the worlds largest cruise ships. They use large electric motors in pods hanging under the hull with direct drive or geared propellers. They have two pods that are fixed and two pods that are independently steer able. (I’m not sure if this (pods) is the proper terminology.) These electric engines are powered by large onboard diesel generators which also provide power to the ship.

    What if you build a system that has an electric or hydraulic motor encased in a unit that attaches to the transom behind the rudder and then lowers down into a fixed position for motoring?

    At first I thought of putting the engine in a pod like a huge trolling motor and lowering it into the water…Kind of old-school. This could be run off the house generator or if hydraulically powered then you could have a pump off the house generator that would power the unit. Either way you would have just one power source that would charge the house batteries, run appliances and propel the boat.

    Then I thought that maybe it should have a fixed motor on the transom that would have a shaft that could move (slide) up and down to lower the propeller pod driven by a gear (turning vertical rotation into horizontal rotation). I though about maybe using a enclosed jet drive like a jet ski or a Jacuzzi drive that would encase the prop therefore making it more efficient and easier to house when retracted back up into it’s transom mount.

    Anyway I like the idea of no thru hull connections…the electric or hydraulic component and the retract ability of the concept.

    Any input?
  2. dsharp
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    dsharp Junior Member


    It's called an azipod. Never seen one on a small boat although you may could convert something like a bowthruster, it has a similar design. Vetus makes them in electric and hydraulic. I think the problem with electric would be the size of the motor required to put out enough power.
  3. jedclampit
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    jedclampit Junior Asparagus

    Yes that is what I was thinking…the bow thruster concept. Sailboats only require small amounts of power…thus a larger boat’s bow thruster might be the ticket. I was thinking for boats under 10 meters…or 30 feet. Approximate size would be 40 hp.

    I guess that the trade off would be the extra weight of the electric motor and the electrical alternator. And of course there is the additional maintenance of the three components vs. just the engine in a typical drive train system.

    Maybe the Hydraulic systems might weight less. I’ll have to look for some components to see what the actual weight would be. I know a mechanic who built an off road truck with hydraulic motors at the axles and drove them off a pump on a diesel engine. Top speed was low but the thing would climb a tree.
  4. jedclampit
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    jedclampit Junior Asparagus

    Thanks for the line on Vetus...they do in fact have a hydraulic system that could be modified or incorporated into my original concept. Now I need to find out cost... Weight seams not to be the issue.

    There seams to be many benefits to the hydraulic system as well; propulsion, anchor windlass, bow thrusters, outdrive lift (my concept) and my favorite idea was to use a hydraulic ram to raise and lower the mast… I guess that you could also make a heavy pop top by raising the roof of the cabin with rams… and all these can be run (one at a time) without any problems…

    I kind of like that idea. Maybe a small alternator could be run off the main engine to charge batteries and run appliances as well…

    Cool, I’ll keep researching! Thanks again...

    Here is the link: http://www.vetus.nl/indexns.asp?lang=2&productid=19

    Hydraulic marine propulsion


    In a number of cases it may be highly recommendable to drive the propeller shaft by means of a hydraulic motor, instead of by the conventional in-line arrangement of engine and gearbox.
    One of the major advantages of hydraulic propulsion is the fact that there is absolutely no need to position the engine in line with the propeller shaft.
    As a matter of fact, the engine may be positioned in any place, deemed convenient, even athwartships.
    In the case of the propeller becoming jammed on rocks or in the mud, there is virtually no risk of damage for the shaft assembly, the hydraulic motor or the main engine itself, as an integrated by-pass valve will then eliminate any force which the hydraulic motor may exercise on the shaft assembly.
    Especially in the case of hire craft, this has clearly been established as a great advantage. The hydraulic motor is engaged in a smooth and noiseless manner.
    The assembly as such operates completely free of vibrations and the thrust of the propeller is not transmitted to the propulsion engine, but to the hydraulic motor, which is flexibly mounted on its own bed.



    A hydraulic vane pump (4) is fitted to the engine in the place of the gearbox.
    This pump (4) draws its hydraulic fluid from a storage tank (3) with integrated oil cooler and presses the fluid into a hand-operated steering and controlling valve (2).
    From this valve, the oil flux is directed, left or right, to a hydraulic vane motor (1).
    This hydraulic pump drives the propeller shaft directly. The VETUS system uses hydraulic pumps and motors with a fixed swept volume. The transmission ratio is
    constituted by the difference in swept volume of the vane pump and the hydraulic motor. The reduction of the number of revolutions of the marine engine to the number of revs. at the shaft is set at 1,9 : 1.
    The maximum revs. of the main engine must be set at 3.000 r.p.m.
    The maximum engine power amounts to 50 kW, meaning that a shaft diameter of ø 25 mm will be sufficient in most cases. The outgoing flange of the VETUS hydraulic motor fits all VETUS flexible couplings.


    One of the mechanical VETUS Stainless steel VETUS
    remote controls, hydraulic storage tank. hydraulic vane
    will regulate shaft vane motor pump
    speed and direction
    of rotation.


    Scope of Supply
    VETUS hydraulic propulsion is available in 3 versions:

    Model HPM 4.15 Model HPM 4.17 Model HPH 4.65
    is suitable for is suitable for is suitable for
    engines up to engines up to engines up to
    24,3 kW (33 hp). 33.9 kW (42 hp). 48 kW (65.3 hp).
    - A hydraulic vane - A hydraulic vane - A hydraulic vane
    pump pump pump
    - A hydraulic vane - A hydraulic vane - A hydraulic vane
    motor motor motor
    - A control valve - A control valve - A control valve
    - A storage tank - A storage tank - A storage tank
    - An oil cooler - An oil cooler - An oil cooler


    1. Hydraulic motor
    2. Hand-operated
    control unit
    3. Stainless steel
    storage tank with
    integrated oil cooler
    4. Hydraulic pump
    5. Remote control
    for the engine
    6. Connection for sub-3
    7. Control unit for sub-drives
    8. Bow thruster
    9. Anchor windlass



    Code Description Export price in euro
    Excl. VAT


    HP/kW Max RPM Reduction

    33/24.3 3000 2,0:1
    Prices on request
    42/30.9 3000 2,0:1
    Prices on request
    65.3/48 3000 1,9:1
    Prices on request

    STANDARD SPECIFICATION INCLUDES: Marine diesel engine suitable for hydraulic propulsion including hydraulic vane pump, s/s 35 litre hydraulic oil tank and hydraulic motor for propeller shaft propulsion. The diesel engine will be supplied with four flexible engine mounts and MP22 instrument panel.
  5. Oyster
    Joined: Feb 2006
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    Oyster Senior Member


    These folks are like an encyclopedia for electric drive train. Take some time and swap a couple of mails with them, You would be surprised how economical a package is for a 30 footer or less sailboat or even a launch type hull..
  6. jedclampit
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    jedclampit Junior Asparagus

    Great Idea Oyster...Thanks I will send them an email today...

    Thanks again, and I hope there's no hard feelings? I didn't want to upset anyone.

  7. Oyster
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    Oyster Senior Member

    No problem here. Sawing up new boats, or reading about it, is like scratching fingernails on a blackboard for me, though. We are have to half cracked anyway for being in this crazy addiction. You will find that I am worse than an enviromentalist when it comes to even one extinction of a species, such a hull as the one represented in your previous posting. The course of least resistance is only temporary for the mind, but will sometimes haunt you down the road. WHile there are times to do so, I am not sure if that fits your situation, from afar, anyway. Nice for me to say that, I guess, since its not my money. Smiles and Cheers
  8. robbieroneill
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    robbieroneill Junior Member

    Volvo has been making drives and pumps since the 70's for small boats (-15m)
  9. Guillermo
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    Guillermo Ingeniero Naval

    Maybe you would like to investigate on RIM trhusters:
  10. jedclampit
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    jedclampit Junior Asparagus

    Way Cool!

    I do like the Azimuth Thrusters. Very cool idea. The retractable concept is very appealing for the motor sailor or sailboat. I don’t think that steering capability is necessary, but would be a nice luxury when docking.

    I also like the concept of the rim drive, however I think this also would be great if it was Hydraulic powered. I am of the opinion that I will be using a hydraulic powered system for the benefit of other needs aboard.

    I don’t like the uncertainty of the design being such a departure from the norm that you could not find a local mechanic to aid in repairs when you are in remote areas of the world.

    Thanks for the link…

    I will write them to see what a small 40-60hp system would cost.
  11. DanishBagger
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    Location: Denmark

    DanishBagger Never Again

    I know it's not podlike, but have you checked out solomon technologies?

    As a little side-note, being electric (having torque all the way from the bottom of rpms) much less horsepowers are needed. So if you go ask for a "40-60hp", then go ask for "the equivalent to a 40-60hp diesel/gas engine". That way you won't have it overpowered and it won't weigh too much.

    Maybe even ask on of those trolling-outboard manufacturers if they can make the drive itself larger, fitting your demands.

    Btw, there's an old, HUGE thread where solomon's "eletric wheel" is discussed, right here on this forum.
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    FAST FRED Senior Member

    What advantage do you hope to gain with the extra complexity of this , compared to a shaft ?

    The cruise shjips can handle any expense as their pods will drive them 3 1/2K sideways (NO EXPENSIVE TUGBOATS) while docking.

    The hotel and push loads vary by a large order of magnitude , so 3 to 15 generators are used as needed, the gensets can be properly loaded and secured when the load becomes too light.

    Depending on the HP required an outboard leg that can spin the desired diameter prop can easily be coupled to a hyd motor.

    But the efficency will be at least 20% worse (high fuel burn) and perhaps weight as compared to a common shaft & prop.

  13. robbieroneill
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    robbieroneill Junior Member

    See http://www.whisperprop.de/ for the small boat azipod data.
    This is agreat system for small boats (-15m)
    I am building a boat for European Canals and rivers see www.robandmarlane.com
    Problem: a 25 ton boat with a 100hp diesel on a 2:1 gearbox turning a 60cm x60cm prop is the boat goes 5kph at idle. That is the maximum speed limit on the canals in southern France. While navigating shallow twisty canal at idle, the motor gunks up, the alternators don't charge well and it is a constant shifting from fwd to N. to rev and back to fwd again. One needs the 100 hp. power to navigat rivers and coastal cruising.
    So how to go slow? The Diesel Electric solution with two gensets; a small unit 15kw and a large 35kw on the same grid to turn a 50kw azipod w/60x60cm prop. Use the small generator to go slow and both or the large to go fast easy enough. But the Domestic AC/DC ring is another problem. The Azipod uses 430vdc, how to convert to 12vdc or 220ac 50hz.? for 30amp domestic power? Fischer-Panda says buy another Genset for domestic power! I don't think this is the best solution, but they do sell generators as a primary business don't they. Got any ideas?
  14. brian eiland
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    brian eiland Senior Member

    Diesel-Electric Canal Boat

    Hello Robbi. I might suggest you utilize the "search" function key on this forum and look up "diesel-electric". You will come up with lots of info on a great number of subject threads.

    Here are a few I might recommend:

    try this reference also http://boatdesign.net/forums/showpost.php?p=44393&postcount=2

    Sorry, a little short on time at the moment, but I do believe this is THE IDEAL solution for your utilization.

    I do need to keep in touch with your website as I have always dreamed of doing a trip thru France on a canal boat with a bicycle for short side excursions.

  15. jedclampit
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    jedclampit Junior Asparagus


    As to reasons to opt for hydraulic power over electric, as you know alternators and electric motors are not efficient (at best 80% both generating and powering) and the weights of units in the 40 to 100 hp range are quite large.

    I need hydraulic power for other applications onboard and the weights of the motors and pumps are not extravagant therefore I think that this is my best solution.

    Hydraulic motors and systems are light weight and cheep. As an example a twenty horse power motor weighs less than 20 pounds and is under $500. Locating a spare on board is not a problem; however a twenty horse power electrical motor weighs about 800 pounds and is well over three grand. A complete hydraulic system with a complete backup system is less weight and less cost than a single electrical drivetrane system.

    I also want redundant systems and hydraulic components can be ganged and valved (backups) and easily modified on the fly if there is a need, however if you should kill the alternator in a diesel-electric system, there is no way to get power without having a very very long cord.

    I am planning on having a secondary hydraulic pump or system on a smaller diesel genset that could provide enough power for minimum propulsion and the other systems if the main system should fail. This smaller system will be utilized while offshore under sail or moored and propulsion is not required.

    Also the main power plant will have a small alternator that will provide dc for the house panel and for battery charging thus two redundant systems without a lot of excessive weight.

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