old heavy"lugger" vs high reving & more hp

Discussion in 'Diesel Engines' started by globaldude, Apr 7, 2006.

  1. globaldude
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    globaldude court jester

    Hi guys, I read various post and just hope that some of you very talented & experienced people can give your opinion as to which way you/they would go .
    I have in my posesion [ sp?] a JP4 Lister 40 hp with a hyd- box, it weighs in at 1.5 ton .I brought it because it was cheap, $750, and has one hour on it's meter [ seems lijit given it's history]
    I had intended to fit a diesel / electric drive system [ and may still ] but when this engine came up I thought ;
    1;It has a great name for reliability

    2; even though it's heavy, I could then use less balast - my 50' yacht is designed to have 4.5 ton of lead, so why not less lead [ @ 750 it's cheaper than lead ! ]

    3; it would be down low and fairly central .

    4; I can forget the more complex issues of the hybrid , therefore getting on the water faster . [ my boat is only a hull & decks at this stage ]

    5; I can only spin a 24" prop and the enormous torque of this engine would would seem to be ok , direct drive . [ as would an electric drive ]

    BUT BUT BUT, it takes up a lot of room, it's heavy [ can't get the weight as low as lead ] wouldn't be running at peak efficiancy - as would a [ quieter ]gen set to power [ at "cruise"] the electric drive and or charge the batterys/balast.

    Thoughts and opinoins please.
     
  2. antonfourie
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    antonfourie Senior Member

    I would go for a lighter engine and have the weight in the keel where you want it.
     
  3. globaldude
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    globaldude court jester

    Ah, sorry, I should've made it clear re my boats design.
    She only draws 850mm with her centre board up !, and the 4.5 ton lead balast is/was to go in her shallow bilge. The engine would be well down in said bilge [ yes I'm a bit concerned about any water sloshing about in such a shoal bilge, but there shouldn't be any !!]

    If it were a deep-ish keel, yes the balast should be as low as possible.
    She is flush decked [ lots of boyancy - & room] and I'm going away from the original design in that I'm taking out the centre board [ takes up huge amount of room & makes big boat lots of small rooms ] and fitting twin asemetrical lee boards.

    Hey I see you're a pom, what's your opinion about this engine ?
    I've had two opinions re the Lister from two pommy mates [ both whom have done extensive sailing and are experienced nautical types ] as to it's reliability !
    One says they're the best , the other says they had a problem with leaking injectors [ if they weren't used often - otherwise they're good] and he's personally seen a cylinder head blown off by dribbling injector allowing too much fuel into the combustion chamber .
     
  4. longliner45
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    longliner45 Senior Member

    fuel in diesle engines explode under pressure about 17lbs per square inch. what fuel that is not burned is returned to the tank. dont see how too much fuel in a cylinder can blow off a head. ,,,would question my source, remember only so much air and fuel will burn,the rest goes back. also are you 100 %sure of the wieght of you engine and tranny? placing a large weight above the keel will defeat the purpose of the keel,remember I am not a designer,,,good luck longliner,
     
  5. bilgeboy
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    bilgeboy Senior Member

    Longliner,

    I think Globaldude is more correct on this one. Excess fuel in the cylinder can do alot of expensive damage. You can put pyrometers on the exhaust gas to try to detect overfueling before its a problem, and thats a pretty inexpensive way to avoid this problem.

    The returned fuel is a neat little built-in lubrication system for the injector, and never enters the cylinder. Once that happens, there is no going back.


    G-dude,

    I always say, "a diesel in the hand is worth two in the yacht of dreams". You are going to have so many other problems to occupy your mind, go with the easy solution to this one. Its natural to dream about the best case scenario. In a way, thats what boatdesign.net is all about. But then you've got to build it! I think you should move on to the next step. If it is at all a real issue, your next boat will correct for this and the other 50 things you could have done differently. Think about it while you cruise around in this boat.

    Any engine can blow up if neglected. Diesel shops around here test injectors for free, you pay for the work on the bad ones. Pop them out and get them checked out. I think it is far more common to have a black smoke condition WAYYY before you will blow the head up. That's an unrealistic outcome for a neglected engine, and an impossibility for the maintenance hungry do-it-yourselfer that you are.

    Mike
     
  6. longliner45
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    longliner45 Senior Member

    yes you are correct I was wrong,,,,anything can happen to anyone at anytime,anywhere,,,,or is it just me?
     
  7. Guillermo
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    Guillermo Ingeniero Naval

    G-dude
    I find it an acceptable option for an internal ballasted boat, probably allowing you to save some hundreds of kilos from the lead ballast (A proper calculation will be needed). If the engine is in good condition, the Lister solution will help you to keep things in a KISS way.
    Check the 24" propeller limit before.
     
  8. FAST FRED
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    FAST FRED Senior Member

    These engines are of quite odd design so would not be as efficent as a modern one.

    You may get 15hp for each gallon of diesel it eats ,
    while a modern aftercooled ,"lectric injection turboed lightweight may get 24hp.

    But your Lister will work AFTER the lightning strike , the modern one ?? perhaps not.

    FAST FRED
     
  9. globaldude
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    globaldude court jester

    thanks fred, for making me feel better that is.
    I brought the engine from a "mate" of mine and found out a few days ago he'd gone and sold the bloody thing AGAIN to someone else. [ I didn't pick it up strait away - 1.5 ton of it - so he figured I didn't want it !!.
    At least he has a concience and when needled he pid me the $1000 extra he got for selling MY engine .
    So looks like he's done me a favour . Back to the diesel / electric thinking , love the regeneration aspect - "free" / parasidic energy.
     
  10. FAST FRED
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    FAST FRED Senior Member

    "love the regeneration aspect - "free" / parasidic energy."


    You're dreaming of course,

    if you use the shaft and prop to run an alternator the prop works as a VERY efficent Speed Brake.


    To contemplate the speed reduction, tow a heavy duty pail astern the same diameter as your propellor , and remember the filled pail is "stalled" the turning prop is far more efficent at pulling out power , slowing you down , even in half a gale.

    There aint no free lunches, unless your a buro rat feasting at the public troff.

    How much does your boat displace in long tonnes?

    About 3X that amount makes for a fine cont HP number to look for.

    5x the tones disp and you have to be a Yank , and love really big stern waves and big fuel bills.

    Why not get a truck engine & marinize it? Or look for a boat running takeout with low time?

    FAST FRED
     
  11. Guillermo
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    Guillermo Ingeniero Naval

    I think 2*Disp is quite enough to run a 'normal' displacement hull even over Fn=1.34 ; betwen 2 and 3 is a trend nowadays, certainly, but not really justified in my opinion for an efficient globetrotter, if that's what we are talking about; and over 3 we have a clear excess of power unless for semi-displacement and planning boats.
    By the way, I'm not used to imperial units. I understood we should talk about 'long tons' and not 'long tonnes', as 'tonnes' is metric. Am I right? :confused:

    Globaldude:
    About the propshaft alternator you may be interested in reading this:
    http://www.sailnet.com/collections/gearandmaintenance/index.cfm?articleid=ouread0028
    Cheers.
     
  12. FAST FRED
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    FAST FRED Senior Member

    The rule of thumb is broad and any weight chosen (for a ton) between 2000lbs and 2400 lbs will give the same (broad) result.

    The modern boat has far higher demands for service than the old sail auxileries, so needs hotel power while the main is on.

    Engine driven air cond ,or refrigeration , hyd systems for roll stability , electric cooking & hot water heaters and de salination gear , are just a START! Dont forget the hot tub!

    Sure would be an embarasement to loose a Knot every time cookie turns on the range.

    FAST FRED
     
  13. Guillermo
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    Guillermo Ingeniero Naval

    Well, I may accept an HP/D ratio between 2 and 3 to allow for some hotel power. But if you have to run a big engine when sailing under sail alone, or at anchor, only for hotel reasons, that's not very efficient. To that end is better, in my opinion, the use of an auxiliary.
     
  14. FAST FRED
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    FAST FRED Senior Member

    "To that end is better, in my opinion, the use of an auxiliary."

    Even better is a design that does not require a noisemaker (auxilary generator) for anchored service.

    Not hard to do , depending on the number of days between main engine operation , for those that can forgoe the Jaccuzi and electric range.


    FAST FRED
     

  15. globaldude
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    globaldude court jester

    thanks Guillermo for the link, I copyied a bit to get a responce from Fast Fred;

    Using the instrumentation on Calypso V (boat speed measurable to 1/100 knot) we have never been able to detect any difference in boat speed between having the propshaft alternator “On” or “Off." Remember, however, that the fixed three-blade propeller (22-inch diameter x 19-inch pitch) is freewheeling in any event. Why not capture all that available power?

    I was going to ask you Fred, why , and I've heard it said before, do you say that a free wheeling prop induces far more drag ??.
    surley the rotating prop is, to more or less degree, corkscrewing through the water and therefore offering less resistance !?.
    In other words, the resistance is pushing / rotating the prop and the prop is yeilding to the preasure, thereby offering less resistance -- yes no !?.
    If the prop were to turn in time with the water speed, there could be no argument that it was causing resistance [ apart from it's wetted surface ].
    So dosen't it follow that the more it turns , the less the drag ?.
    I don't know if that's right , it just seems logical to me .
     
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