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Hull Speed

Discussion in 'General Yachting Discussion' started by NorCalBoater, Dec 24, 2012.

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  1. Marmot

    Marmot Senior Member

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    Percentages smercentages, it reads like a bunch of nominal smoke for some reason ...the load is what the engine powers, it can't produce any more or any less than the load imposed on it ...
  2. NorCalBoater

    NorCalBoater New Member

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    Thanks for the response. This is what I was looking for. Not sure what the other guys are arguing about.
  3. talexander38

    talexander38 Member

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    and here's something real simple to do, the next time you haul out have a cheap Rv level handy. Have the lift operator level out your boat and install it. I have one installed and it reminds me when I put just a little to much power to her. The bubble goes forward as the bow goes up...simple but it works...:)
  4. Marmot

    Marmot Senior Member

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    Accelerate that same device along a perfectly level surface and the bubble will move forward too ...
  5. Capt J

    Capt J Senior Member

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    Commercial rated diesels are generally designed to run at 100% throttle, these are usually found in commercial boats.

    E rated- or pleasure craft rated diesels are recommended by the engine manufacturers to run at 80% load, and you can run them for 100% load for an hour or less typically as recommended by the manufacturers. These are usually found in 95% of the yachts you see running around under 150'. Most of your Westports and such still have E rated diesels.

    A C-rated engine is rated for a lot less HP in the same engine block/components as an E rated engine.

    As for what restriction on a waste gated turbo. Well, the airflow has to go through a lot more tubing and bends, even if it is being waste gated or bypassed at the turbo. You still have an intercooler to run through, etc etc......Larger injectors as well that are running at a less efficient duty cycle.

    Some of the additional HP that a turbo makes, is negated by the increase in heat created in the intake air by compressing air, and is also sometimes dealt with by a richer air/fuel ratio to cool off the combustion temperatures. Below the turbo's and in a no boost situation, the computer is not trying to cool off the compression of air with additional fuel. Granted intercoolers andaftercoolers help with this. The cooler the intake air is, the denser it is and the more HP the same engine can and will make until you get into the limitations of the intake and exhaust system.
  6. PacBlue

    PacBlue Senior Member

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    I believe you will find that the CAT letter rating will not directly apply to the MTU powered Westports. While both can be considered pleasurecraft or a high performance ratings, the MTU application will not have a restriction on operating hours at 100% load, as the 1 hour or less verbage is a CAT requirement. You can run the MTU at 100% as long as you want, although you will be reducing the Time Between Overhauls, as it would on any engine. Westport has a 20+ knot requirement and thus the need for them to use the high performance rating.

    Christenson uses true continuous rated commercial engines as they are targeting more displacement type speeds, closer to Hull Speed as this thread topic. You will also see Delta and Trinity with a mix of continuous rated commercial product for their displacement applications and other high performance rated product for their +20 knot applications. Palmer Johnson has been on a hi-speed path for quite a while (although they have some recent displacement craft in the works as well) and they have been fairly exclusive with high performance rated engines.
  7. talexander38

    talexander38 Member

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    it works for me, if not in true attitude, then as a reminder..I have a heavy hand..
  8. 84far

    84far Senior Member

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    There seems to be two answers here.

    Hull speed - What the boat was desiged to do in regards to speed. Then there's also speed predictions - V = C x square root of, shp / disp

    Efficiency - Running at max hull speed, will usually mean huge fuel burn as Pacal says. I'm guessing an engine supplier should have specs on the motors most efficient rpm.

    Far
  9. Marmot

    Marmot Senior Member

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    You are seriously confusing spark ignition (gasoline) engine operation with that of compression ignition (diesel) engines.

    Back to the books, lad.
  10. Scottbee

    Scottbee Member

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    Marmot,

    Personally I would love to have you expound on that. You clearly have some information and education that go beyond mine (and Capt J's I guess).

    I would think that intake charge density as effected by air temperature would essentially be the same for almost all forms of ICB's, with similar results. And I have seen the effects of altering the stoichiometric ratio on both EGT's and pre-ignition in non-spark engines.

    What am I missing here?

    Thanks!
  11. Pascal

    Pascal Senior Member

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    What some are missing is that a few % of efficiency is barely noticeable compared to running 1/4 knot over HS, or with trim tabs down or a little growth on the wheels!

    It s mental masturbation, nothing more, although deeply pleasurable to those doing it
  12. talexander38

    talexander38 Member

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    amen !
  13. Marmot

    Marmot Senior Member

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    That is a neat trick. Considering that there is no fuel in a compression ignition engine to ignite until ignition is desired it is kind of hard to achieve pre-ignition.

    There is no fuel in the combustion chamber until the instant that combustion is desired. Not only that but since the ideal diesel fuel has the absolute minimum possible ignition delay it is difficult to achieve better than the ideal desired.

    Stoichiometric? Considering a diesel injection period covers several degrees of crank angle and there are plumes of fuel droplets surrounded by fresh air, the "mixture" is stoichiometric in the fringes, too lean nearly everwhere else, and too rich in the body of the spray. There is no "mixture" to consider.

    Until it reaches the "smoke point" a diesel always has an excess of air in the combustion chamber. The ratio of fuel to air only defines the end limit of the weight of fuel that can be burned. Excess will just create smoke and soot. Less fuel than that point will produce less power, that's all.

    Nearly all of your comments apply to gasoline engines, not diesels.
  14. Scottbee

    Scottbee Member

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    I'm sorry... but you're implying that all diesel engines are direct injected units.... and that is far, far, far from the truth.

    But if you want that to be a constraint for this conversation, I understand. My comments were with respect to a broader base.
  15. karo1776

    karo1776 Senior Member

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    Where's Nilo in this discussion he should know the story on tailoring diesel and vessel performance... ???
  16. Marmot

    Marmot Senior Member

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    About 9 percent of the diesel engine population overall uses indirect injection. About 10 percent of the small recreational engines and 4 percent of commercial engines. Your broad base fits on the head of a pin and the type of injection doesn't change the way a diesel engine works.

    For some reason you believe that diesels deliver, ignite, and burn fuel the same way as gas engines. They don't. Period. Goodnight.
  17. Capt Ralph

    Capt Ralph Senior Member

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    O K, you hooked me (I'm an idiot). Who (what, whom) does not inject diesel in a motor boat engine?
  18. Marmot

    Marmot Senior Member

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    Owners of carbureted gas engines. ;)
  19. Scottbee

    Scottbee Member

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    No, you're not an idiot at all.... (obviously).

    My background is not in marine diesels. But since I'm probably soon to be the owner of one (OK, 4), I figured I best learn a thing or two. And I appreciate your insight and information.

    So if I understand you correctly, on these direct injected diesel engines, when the fuel injection is "excessive" (based on load, RPM, temp, etc..) the engine will generate smoke and soot.... but will not show a marked drop in EGT or general combustion chamber temperatures. And when the injected fuel quantity is "deficient" (based on the same parameters) there will be a reduction in output power with no marked increase in EGT or general combustion chamber temps. Right?

    This is not a trick..... I am learning the difference between these engines and what I have worked on in the past. And since there is no intake air metering, what your are saying (if I understand you correctly) makes some sense.

    Thanks!