distributed hydraulic systems on boats? why not?

Discussion in 'Boat Design' started by ijason, Jan 24, 2009.

  1. ijason
    Joined: Jan 2009
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    ijason Junior Member


    as a heavy-equipment operator for some years now, i've gained a huge appreciation for hydraulics. and as an utter novice in all things nautical, i've got some questions about how the two subjects might get along.

    almost all of my boat knowledge is from the internet, so please do correct any misunderstandings i have :) it seems to be there are several considerable advantages to using a distributed hydraulic system to do much of the work on a boat, with relatively few disadvantages. i'll make a list for easier refutation!

    1) wear on the engine. when you tie an engine to a hydraulic pump, that engine will almost always run at a steady rate. there is no revving up or down as all throttling is handled by the hydraulic pump. this clearly means less wear on the engine in terms of needing it to run at any speed other than it's optimal rpm. also, having your engine and hydraulic pump connected to other devices via lines instead of mechanical linkage isolates the engine from vibration imparted from the propeller or waves.

    2) more options to locate your engine. if you're free from needing a linear connection between your engine and your drive propeller you are free to mount the engine in a way that makes maintenance easier. big plus there! it also gives more options for sound insulation and water-proofing your engine compartment.

    3) no direct linkage between engine and prop. by using a hydraulic-drive motor to run the prop you eliminate the chance of damaging your engine/transmission by fouling your prop onto rocks or chain.

    4) you can use your engine for more than one thing. you could power bow-thrusters, winches, deck-cranes, or any number of systems from the same hydraulic pump that runs your propulsion. keeping things simple means less spare parts to take, and less things to go wrong.

    5) heck, you could even replace your generator! tie a generator head to another hydraulic-motor and you can say goodbye to needing an entirely separate generator. simply run it off your main engine.

    6) hydraulic lines don't mind getting wet or short out. this seems like a huge advantage to me. just for the safety aspect of things, if you lose a hydraulic line you end up with a mess, but no chance of electrocution.

    7) you can get better health readings. if you put an inline pressure-gauge on all your systems you can very easily establish a normal operating pressure and any deviation from that pressure would immediately indicate problems with the system, the pump, or a system leak. something much more difficult to determine with many mechanical systems.

    all of these seem to be pretty substantial advantages. of course, if it was a perfect solution everyone would be doing it! so here are the disadvantages that are obvious even to me :

    1) weight. this would add weight to your boat, and potentially in substantial ways. while i think the advantage of having one drive motor may help off-set the issue, there's no doubt that a hydraulic-drive motor is a lot heavier than an electric.

    2) many people are unfamiliar with hydraulics. at least, compared to electronics. if you've got a pair of dikes and some electrical tape you can work on electronics, the skill-set to trouble-shoot and repair hydraulics is a bit broader.

    3) lack of redundancy. if you've only got one main motor and one main hydraulic pump attached to it, you're out of luck if either fail.

    i'm sure i've missed many obvious things, but it seems to me that the advantages out-weigh the costs... and yet, i've seen almost no mention of hydraulic systems on boats. there must be a reason!
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  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Hydraulic systems, including drives are being employed on yachts. Everything from winches and sail handling to drive systems. Drive system draw backs boil down to efficiency loses, which are higher in comparison to more convention systems, which is why you don't see the market flooded with pump driven devices.
  3. Guest62110524

    Guest62110524 Previous Member

    yeppers Par is onto it, but ALL superyachts make use of hyds, espcially for sail handling, up keel, up dining table etc, all manner on things, from thrusters to captive reel winches
    I did however build two boats which had hyd out drive, they were mussel harvesters, the leg (like outboard) could raise up and down, the motor was in the leg driving the prop(see in my galllery
    IF main propulsion was viable ships would have done it way back
    i love hyds, especially for sheet and halyard winches, they dont get tired Of course these are not M/E driven but run from a DC pack. But the DC motor is big and strong, drives the pump , whereas electric winches have smaller dc motors at the winch itself, and they get tired
  4. Fanie
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    Fanie Fanie

    One drawback would be that you have to run the hydraulic pump whenever you want anything, however small, to run off it.

    With electric equipment you can use batteries for stored energy, and besides a generator solar panels and wind power generators amongst others can recharge the batteries.

    You are right in that hydraulics packs impressive power, but it may not always be the right thing. In my experience, I have never seen a clean leak free hydraulic setup. May be I just never was in the right place :)
  5. TeddyDiver
    Joined: Dec 2007
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    TeddyDiver Gollywobbler

    1)Hydraulic motor/pump combination is much lighter than any electric counterpart
    2)It's allmost as easy as plumming
    3)Boat having enough size to such system can easily have also other smaller unit

    It's better to have a closed circuit system and variable displacement pumps (and possibly motors too). It's has much better effiency. Considering the advantage of running at best rpm (not steady) it could be allmost as efficient as diesel-electric.
    Major drawback is heat.. Noise maybe other (needs a lot of precaution)
  6. ijason
    Joined: Jan 2009
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    ijason Junior Member

    i think the most amazing thing about hydraulic options is the relatively tiny size needed. you can run a hydraulic wench off of a power-steering pump in a truck, as long as it can push 1gpm of steering fluid through the motor. with gearing you're looking at 4 tons of torque from a hydraulic motor the size of an alternator needing only 1gpm of flow. wouldn't take a very big motor at drive such a small hydraulic pump!

    @fanie : you're absolutely right about hydraulic systems tending to be a bit messy. usually though it's not due to actual leaks as much as seeps in the pump or actuators... a leak will be immediately obvious as a lack of power, and there tends to be catastrophic failures shortly after a leak - leaks in hoses, at least. the standing joke is that if you ever think you have a leak in your lines is to just look for the clean spot.
  7. TollyWally
    Joined: Mar 2005
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    TollyWally Senior Member

    Small Hydraulic systems are used everyday with great results on small fishing boats. Larger boats use larger more sophisticated systems. Typically on a small boat (gillnetter etc.) the hydraulic pump will be belt driven off the main engine with an electric clutch. The pump freewheels unless the switch is thrown then the hydraulics kick in.

    Hydraulic systems for winches, bow thrusters etc. are far superior to electric models. I am always amused to see "gold plated" yachts with their silly little toy electric winches and thrusters. Go down to the commercial docks, you'll see hydraulics till hell won't have them.
  8. Guest62110524

    Guest62110524 Previous Member

    I use ss tube and flares, flarews cost zilch, , so all the lines running the length of the boat are ss, the only drawback is you have to flare in a vice, the tool a simple punch with the female machined in, and a split block, with goes around the tube, one whack with hammer and theres a 5000psi working pressure flare Swageloc thingies are expensive and not so reliable. then a short hose onto the power pac and winches etc Fanie, or was it manie, you only use you M/E for the anchor setup, the rest is electro hyd power pack
  9. pogie joe
    Joined: Jan 2009
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    pogie joe remember

    I can remember in the early 80's a new state of the art fishing trawler showed up on the waterfront in Gloucester Ma. This Dragger was rigged with hydraulic generators in those days it was common to run a gen set 24-7 even when tied up. Problems started when the temperature began to drop, If they swapped generators from port to starboard or viceversa the hydraulic motor on the generator would crack. After replacing about a half-dozen motors they realized that it was the hot oil hitting cold generator. Well the long and short of it is, the hydraulic generators came out and diesel generators went in.
  10. ijason
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    ijason Junior Member

    @pogie : hmm? i'm not doubting the story, but i'm a little confused by what you're referring to as a hydraulic generator. do you mean a generator-head driven by a hydraulic motor, or are you using the phrase "hydraulic generator" to mean a hydraulic pump?

    i can't imagine why you would switch from one hydraulic pump to another? and, if a hydraulic motor was tied to a generator head it wouldn't crack when you powered it up just because the oil was hot.. at least from my limited experience with construction equipment.
  11. pogie joe
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    pogie joe remember

    Jason, yes i am referring to a generator that is driven by a hydraulic motor it is very common to switch generators to give them equal time. "Why were the motors cracking" hard saying not knowing but it only happened when the motors were cold and the oil was hot! Perhaps it was a bad casting i really don't know that either.
  12. ijason
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    ijason Junior Member

    @pogie joe. i can only imagine the sinking feeling when you heard that first pump crack.. and then how immeasurably pissed i would be at the 2nd and third! losing a hydraulic motor is probably a good bit cheaper than losing a generator though.

    is it common to need to rotate generators that way? do they heat up more quickly than the type you would see at the hardware-store on a little cart?

  13. Tad
    Joined: Mar 2002
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    Tad Boat Designer

    The last major sailing yacht I was involved with (154' ketch) had dozens of hydraulic functions....cylinders and motors.
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