Fuel burn on 70'+ Burger?

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)

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

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.

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.

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.

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.

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.

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...

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.

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.

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.......

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.

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.

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.