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Discussion in 'General Yachting Discussion' started by paulga, Nov 26, 2017.

  1. ranger42c

    ranger42c Member

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    What engines, specifically?

    Our Cummins (450C) ratings are quite clear in all their documentation:

    High Output
    This power rating is intended for use in variable load applications where full
    power is limited to one hour out of every eight hours of operation. This rating is
    for pleasure/non-revenue generating applications that operate less than 300
    hours per year.​

    Nothing there about a 10-30% load factor. Clear restriction on using full power (WOT).

    -Chris
  2. Capt Ralph

    Capt Ralph Senior Member

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    Where is the documentation calling for a 10-30% load factor? This is a fast idle and not the best for any engine.
    Or, 10-30% engine time high (max) loaded.
  3. 30West

    30West Member

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  4. Capt Ralph

    Capt Ralph Senior Member

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    So, You can operate at 80% running load all day long, FOREVER.
    Recreational class E (use and duty cycle) allows interment operation at WOT for 1 out of 8 hours of operation or WOT operation (max load factor) for up to 30% of life.
    These are near the same specs all mfg's use for duty class E engines.
  5. ranger42c

    ranger42c Member

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    "High Output (HO)
    This power rating is intended for infrequent use in variable load applications with a load factor of 10-30 percent. Full power is limited to one out of every eight hours of operation. Reduced power operation must be at or below 80 percent load.

    Typical High Output applications are sportfishers, motoryachts, and cruisers."


    I can read that as rated to operate at or below 80% load, but only infrequently as low as 10-30% load, and only at full power 1 out of every 8 hours.

    -Chris
  6. 30West

    30West Member

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    So the 10-30% load factor is a lower limit, the engine isn't to be operated that low for long periods?
  7. Capt Ralph

    Capt Ralph Senior Member

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    The math did not ad up till ranger42c had his eyes on it. Max time under-loading.
    That makes good since also.
    Nobody (or I) thinks about under loading getting documented, so fast reading lost the weight of the Cummins statement.

    Looks like a life (% in hours?) spec is given for slow speed operation from Cummins.

    Not sure I'v read that in duty cycle ratings before. I'll have to go back and re-read a few things.

    But still not telling anybody to run WOT;
  8. Capt J

    Capt J Senior Member

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    The Cummins lingo on that web page is very hard to figure out what they're trying to say exactly.
  9. 30West

    30West Member

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    I've spent decades in parallel engineering/management career, and flying jets. In both, load factor and duty cycles are dealt with constantly, are very specific, and exceeding them can be costly. So I tend to take them very literally. The mushy wording in the Cummins definition is painful. I emailed Cummins for clarification, and they gave me a local sales office to contact. This is unquestionably an engineering issue, not a sales issue, so that is more frustrating. I'll have to pursue this further when I get time.
  10. ranger42c

    ranger42c Member

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    Don't know, but it looked like one way to interpret it.

    Especially in light of commonly-cited strictures against running diesels under-loaded or at lower-then-recommended operating temps for long periods of time.

    -Chris
  11. 30West

    30West Member

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    I've long heard it was bad to idle diesels, but over-the-road truckers idle their trucks all night quite often. As far as temperature, I assume the thermostat would mostly cut off coolant when the engine drops to the set temp, and with no air cooling in a boat, it should stabilize at that temp...? But combustion chamber temps and exhaust temps would be much cooler than when under load.
    Last edited: Dec 23, 2017
  12. Capt J

    Capt J Senior Member

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    Yes, but boat engines are water cooled. On most of the diesels the coolant temps come down when you idle (or never come up all of the way). The electronic diesels have gotten better at maintaining engine temp while idling, but on most of them they're still about 10% less than at cruise......whereas a lot of Detroits would be 30% less.......
  13. leeky

    leeky Member

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    I've been looking at a 2013 Caterpillar Marine Engine Selection Guide that associates the term "load factor" with the type of vessel and not the speed of the engine. Examples of phrases in the guide are "Fast commercial and passenger vessels and cruising yachts with moderate load factors" and "Fast patrol craft and fast yachts with low load factors."
  14. Capt J

    Capt J Senior Member

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    Those are the ratings.......E rating is fast patrol craft and fast yachts with low load factors (this would be the highest HP version of that engine.
  15. paulga

    paulga Member

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    the "loading factor" for High Output diesel is cummin specific. this boat has a 03 Yanmar with stern drive
    • is it in the niche group?
    • should stern drive be avoided?
  16. Capt J

    Capt J Senior Member

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    I wouldn't touch a stern drive on a boat that sits in saltwater year round. The saltwater eats the stern drives alive.
  17. paulga

    paulga Member

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    thanks, this confirms what I got from research.
    i'm looking at a 98 Bayliner , 00 Bayliner and a 99 Sea Ray. I can see the two Bayliners have the same Cummins, the 00 Bayliner is more tidy but also has more engine hours. 99 Sea Ray is a little larger than I want but is otherwise in perfect condition. How to further compare them?
  18. Capt Ralph

    Capt Ralph Senior Member

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    I was just thinking Bayliner Motor Yacht may be something to look at.
    Not the express cruisers that look like SRs.
    Hino, Cummins and others pushed them.
  19. ranger42c

    ranger42c Member

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    Yeah, but I've also begun to hear more recently they're not told not to do that. For whatever reasons...

    And as J says, water cooling is different. Ours won't even come up to temps when idling (or at least it would take a loooooong time); they need a load to get warm enough so the thermostat will kick in.

    -Chris
  20. leeky

    leeky Member

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