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Fuel burn on 70'+ Burger?

Discussion in 'Burger Yacht' started by Andytk5, Dec 30, 2009.

  1. Capt J

    Capt J Senior Member

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    I will run Detroits at 1,000 rpms and then every 4-6 hours bring the boat up to 2,000 rpm's for 30 minutes to clean them out. According to several sources at DD, this is ok to do. Not as ideal as running at cruise all day long, but definately much much better for the engines then running at even slower speeds in the intracoastal for an entire day because at 1000rpms everything does stay at temp.

    It depends, I ran another Hatteras with 8v71TI's that were de-tuned by the DD dealer to run lower rpm's most of the time. The 110 liter per hour injectors were replaced with 90 liter per hour and it ran clean all of the time because the smaller injectors did a better job at metering the fuel at the lower end. At cruise speed it lost 1-1.5 knots.......but the pair only burned 30gph at 1950rpms versus 45gph-50gph before......and sipped fuel at displacement speeds.

    I think Cummin's B series are a great engine, but a bad choice for a 70' Yacht, they just don't have the proper amount of torque. I would rather see a CAT C18, that is detuned to a "C" rating or even lower rating so you still have the displacement or torque, and it could always be re-tuned to an E rating if you chose to do so in the future. ( I think)
  2. dennismc

    dennismc Senior Member

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    If you run 6-71 ti's at 1200 rpm for most of your crising , you might get 1200 hrs before rebuild, big hp requires big injectors which unless electronic controlled will pour fuel into the bores and wash them nice and clean at low rpms, the turbos don't usually cut in till about 1500 rpm and then efficiency starts to build, don't believe me, talk to DD.
    I have 6000 hrs on my 12 71 n's , no smoke, de tuned to 430 hp ea, I run mostly at 10-11 kts at 1450 rpm , average 20 gph plus gen time, I would rather major them than replace with turbo'd engines, my choice based on experience for my type of cruising, which is, Florida, Mexico, PNW and Alaska
  3. Andytk5

    Andytk5 New Member

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    Not too experienced with marine diesels, but determining your cruising rpm and horsepower needs do you get into selecting an injector to meet this and also better atomization because larger injectors under less pressure vs smaller injectors with proper fuel flow?
  4. Andytk5

    Andytk5 New Member

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    As far as the builder seems like the Hatteras is winning out over Burger/Broward for our requirements. Looks like I could run them at lower displacement speeds like the Burger but also have the option of higher top end when needed, or is this the problem someone mentioned about not running these engines at lower speeds? I guess the question I have is if we go with a 70'+ Hatt that can run up to 17-20kts but cruise it at 10-13kts is this actually bad for it?
  5. Henning

    Henning Senior Member

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    Yeah, but I can take a 6-71 TI running at 2100 rpm with a set of 5.90 or so gears and get the same thrust at the prop as your 12-71 NA running at 1450 rpm running likely through 2.80 or so set of gears. I'll do it more efficiently, and that engine was designed to run like that all day long in industrial applications, and there are still a ton of old tugs around the world operating them just like that. I used to run an old tug that had 4 6-71s boxed to a single shaft, push barges for 2 weeks at a time mostly with the throttles on the dash.

    There is no sense in operating an engine that has any more output than its continuous use rating when that rating matches your vessels need. Diesels are designed to just bet turned up to their continuous use rating and left there for days at a time, so long in fact that they are often equipped to do running oil filter changes. They are very efficient at that output as well. You run big engines when you need big horsepower (yes yes, torque, fine, that's what gears are for, HP= Torque * Time). You never want to carry more weight than required, Weight = Drag, this is especially true with a planing hull vessel. Diesels always run lean of peak. You regulate the power output on the fuel side. The engine will make the same power at the same rack setting regardless of how much air I put in the cylinder so long as I have enough to reach to peak EGT/TIT pyrometer readings. The further I go beyond (there is a point of diminishing returns of course, and it's around 150*) though, the cleaner and cooler of a burn I get with a smoother but steeper pressure curve concentrating more of the force in the first few degrees ATDC where they have the greatest effect. You also keep your oil cleaner by not producing as much soot. The turbos allow me to get this air volume to run say 200 hp worth of fuel at 150* LOP at a lower RPM than that required without them. It's a simple matter of volumetric efficiency. The slower I can turn the engine for the same HP, the more efficient I'm going to be, especially driving props.

    You know you can stick turbos on your 12-71 and make them run better/cleaner more efficiently as well.... Just get a set in tune with the gas flows in your operating range.
  6. Capt J

    Capt J Senior Member

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    I run a 75' Hatt at 1,000 rpms 90% of the time....(since fuel prices went way up a few years back)..I burn 1.5 GPM (or less) at 10 knots, at 17 knots I burn 5.5 GPM. I feel that it won't diminish the amount of hours they'll last as long as I run them at 2,000 rpm's every 4-6 hours to clean out the combustion chambers and ports. How many large yachts travel the intracoastal north or south when it's rough and never come about 1,000 rpm's for days and days because they can't. How many sportfish with Detroits troll for 10 hours a day without being run up? Needless to say, the fuel I saved the owner on the Great Loop was enough to pay for Major overhauls on both engines and have 50% left over to major them again. yet both engines are running perfect and show no signs of abnormalty.
  7. K1W1

    K1W1 Senior Member

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    Hi,

    Torque is a moment of force about a point- As a supposed world and everyone beating captain/engineer/pilot/?????? even you should have learnt that along the way.
  8. Henning

    Henning Senior Member

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    And where does what I wrote conflict with that in any way? I was just pointing out that as long as horsepower was equal, the same prop torque can be attained from a higher speed lower torque engine through the proper gear reduction.
  9. Marmot

    Marmot Senior Member

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    Nothing quite like wading in the mud ....

    HP = rpm x T(torque) / 5252(constant)

    Volumetric efficiency of a blown or turboed diesel exceeds 100 percent. It has nothing to do with EGT or what you seem to think is "mixture."

    "Lean of peak" (unless you mean LOP to be lube oil pressure) is a spark ignition measure of fuel mixture, it has nothing to do with diesel operation.

    When there is not enough air to burn the weight of fuel injected a diesel engine reaches the "smoke point." Until that point the fuel will burn (in a properly operating engine with good fuel) at stoichiometric temperature, as high as it can get, and the high temperature is used to heat the excess air to expand it.

    If you get high EGT on a diesel you are operating in overload and looking for problems. You really are confusing a limited knowledge of recip aircraft engine operation with an even more limited knowledge of diesel engine operation and posting nonsense.
  10. dennismc

    dennismc Senior Member

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    And, because it's New Years Eve here in Vancouver, I totally agree...so there..and I also disagree..
    HAPPY NEW YEAR ALL , A great list...
  11. Andytk5

    Andytk5 New Member

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    Does anyone see any issue in towing a 25' twin engine center console behind any of the boats mentioned above in this thread, especially the 75-80'+ Hatteras'?
  12. Capt J

    Capt J Senior Member

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    No, not a problem with the proper tow eye on the center console and proper tow harness. Keep in mind you will need an additional person to unhook it, get into it and run it into marina's and such while you bring the big boat in.
  13. Henning

    Henning Senior Member

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    Not for the boat if it's properly rigged, but for the crew if they're not properly trained. I know one gal that lost her foot to it. Towing has a good few hazards, use a floating tow rig.
  14. Andytk5

    Andytk5 New Member

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    Wow, that is terrible. I have had alot of experience towing behind smaller boats(40'), midsize whalers and small center consoles I was just curious as to if the hatteras could handle it, sounds like it can just fine. I have had to be the tender swim boy a few times when the seas were too rough to bring it alongside the other boat. lol lifejacket...

    Also do many people run the Hatteras 75-80' without crews? My family and I spent many of our summers on our large Gulfstar sailboat, with 25' Mako, and zodiac in the Bahamas and Keys repairing them all ourselves (dad and I) generator, Perkins main, plumbing, a/c etc... Many of the systems were impossible to get to making that the hardest thing about the repairs, seems like the systems are much easier to get to in the engine rooms of the Hatts, is this feasible for someone who is pretty exp repairing that boat?
  15. Capt J

    Capt J Senior Member

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    Yes, both the 70' + 75' hatteras' that I run are also run by their owner/families without any crew on-board. I usually deliver them or pre-position them for the owner's. Yes, most things are easy to get to, to maintain on a Hatteras. If you have a good yachting/boating background it's do-able, it just depends on your experience and how much work you'd like to do. But I'd recommend a full time Captain at least for a year until you figure the vessel out and if you're towing with it and so forth......and until you learn where everything is and how they work.......
  16. Andytk5

    Andytk5 New Member

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    That's exactly what I was thinking too. Have a Captain/Mech basically show me all the insides adn outs from operating to repairing for a year before solo family stuff. Also I haven't really seen any of the one's for sale that have the crew areas converted to more guest cabins. Maybe that is just not feasible, especially if you are thinking about chartering the boat out for a month or two during the year to offset costs, not sure how many people actually do that with a vessel this size or age.
  17. Capt J

    Capt J Senior Member

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    That's because the crew stateroom is one of the guest staterooms or of the same quality. The crew stateroom is actually nicer then 1 or 2 of the guest staterooms on most Hatteras MY because it has a nice sized private head/shower.
  18. Pascal

    Pascal Senior Member

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    no problem running around 10kts... most people agree that a short run on plane at the end of a long day is all that's needed. the key is to make sure the engine (any diesel) is running at the proper temperature, and not on the cold side.

    again, at 13kts, a 70 footer will burn as much fuel as at 17kts... makes no sense. it's EITHER 10kts or 17/18kts...

    a 70footer can be owner operated (assuming enough experience for the underwriter to agree...). The thing to keep in mind is how many hours of a vacation day you want to use up running the boat. it's not about jsut the handling it's everything else... Er checks, occasinonal troubleshooting, rinsing things, doing the trip preparation (finding marinas, provisioning, etc...). to many owners having a captain on board means the difference between a working vacation and a real vacatino.
  19. Capt J

    Capt J Senior Member

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    I agree with this completely. And what to add, it's either 1000rpm's or less, or cruise rpm......The in-betweens are never efficient.
  20. Henning

    Henning Senior Member

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    70-75' is about the break even point on cost between having a permanent crew take care of the boat vs. having a contract company take care of it. It requires continuous care and maintenance, so unless you have a lot of spare time on your hands to do it yourself, you'll need one or the other to keep up on things or the condition and value of your equipment will deteriorate as well as your dispatch reliability. There are quite a few owner operators in this size range though, so it's all in how much free time you have and how much of the work you want to do yourself.