Turbo Diesels

I think the notion of load has to play a part in the “work” that the power plant must perform. WOT does not reflect work on its own.

One needs to take into account props, transmission, and external conditions to determine the load on an engine. Running at continuous high load will cause problems in due course.

Continuous duty-
For use in applications requiring uninterrupted and unlimited service at full power.
Load Factor: 80% to 100%
Typical Annual Operation Hours: 5000 to 8000 hours
Typical Hull Forms: Displacement
Typical Applications: Freighters, tugboats, bottom drag trawlers, or deep river tugboats, dredges
Heavy Duty

For nearly continuous use in variable load applications where full power is limited to 8 hours out of every 10 hours of operation.
Load Factor: 40% to 80%
Typical Annual Operation Hours: 3000 to 5000 hours
Typical Hull Forms: Displacement
Typical Applications: Mid-water fishing trawlers, crew and supply boats, ferries, purse seiners, and towboats. Or auxiliary applications like thrusters and cargo pumps in dynamic positioning.
Medium Duty

For moderate use in variable load applications where full power is limited to 6 hours out of every 12 hours of operation.
Load Factor: 20% to 80%
Typical Annual Operation Hours: 2000 to 4000 hours
Typical Hull Forms: Semi-displacement and displacement
Typical Applications: Ferries, harbor tugs, fishing boats (designed for high speed), offshore service boats, (non-cargo) displacement hull yachts, or short trip coastal freighters.
Light Duty

For intermittent use in variable load applications where full power is limited to two hours out of every eight hours of operation.
Load Factor: Up to 50%
Typical Annual Operation Hours: 1000 to 3000 hours per year
Typical Hull Forms: Planing and semi-displacement
Typical Applications: Offshore patrol boats, customs boats, police boats, some non-net fishing, fireboats, military and police vessels, or harbor tugs. Or auxiliary applications like emergency fire pumps and hydraulic power packs.
Pleasure Duty

For infrequent use in variable load applications where full power is limited to one hour out of every eight hours of operation.
Load Factor: Up to 30%
Typical Annual Operation Hours: 250 to 1000 hours
Typical Hull Forms: Planing
Typical Applications: Pleasure craft, harbor patrol boats, harbor master boats, some fishing or patrol boats, sportfishers, motoryachts, and cruisers.

All and any engines will likely last longest and in best possible condition by always enabling cool down at idle for a minimum of 5 minutes.

This is not rocket science. This is letting the engine's multiple material products' combinations reconstitute back into their relaxed, more normalized molecular positions.

The manual for my Yanmar 6LPA recomends that it be run up to high revs 5 times before letting idle for 5 minutes then shutting down. I feel like a teenager with his first motor bike but gotta assume the Yanmar engineers may just know a bit more than some whose opinions i have read. Certainly more than me.
To minimise my embarrassment i run hard at varying high revs for 15/30 minutes before throttling back to enter the marina. Thus demonstrating that i think i know more that the Yanmar blokes.

sunchaser said:

As mentioned in previous posts, the % load a diesel can safely operate at is all in the Rating. Genset duty, river tugs, dirt moving equipment etc come to mind when referring to continuous full load operation.

For example, one of the best and most popular industrial diesels out there is the Cat 3406. At an A Rating it is designed for 100% load full time putting out around 350HP. Cummins, Scania, Perkins Sabre, JD, Volvo and others make their versions of continuous duty "A" "M" etc rated diesels. All of course have turbos.

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And just to help people understand, the 3406 in a pleasure boat application is an 800hp engine. So you too can have a “continuous duty” if you run the engine at about 45% power....continuously.

Baker said:

And just to help people understand, the 3406 in a pleasure boat application is an 800hp engine. So you too can have a “continuous duty” if you run the engine at about 45% power....continuously.

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Keep in mind, unless you underprop the pleasure version heavily, it's not necessarily the same. If, say, the 350hp continuous version is rated at 1800 RPM and the 800hp version is rated at 2200, then backing off to 350hp output on the 800hp engine will likely have you making 350hp at less than 1800 rpm. Depending on what the durability concerns are on that engine and why it's rated the way it is, plus any differences in the fuel curve on the continuous version, you may still not achieve the durability of the continuous output version. Then again, the 800hp version might have some internal upgrades and when backed off to 350hp it might do just as well even with the RPM difference.

Turbos are a perfect answer for the typical trawler skipper.
Many think they can run rapids and escape weather. Maybe. Once in a great while it’s possible but 95% of the time .. no.
Guys just like to “let-r-rip”. The’d like to go fast most of the time but that clearly burns too much fuel. Cars, boats and even motorcycles.

But compared to NA engines the turbo gives the option of having a smaller and lighter engine that has overall benefits for performance. Overall performance like boat handling and seaworthiness is a plus for most boats.
But the turbo engine is much like a dream come true. More power and less weight.

Nomad Willy said:

Turbos are a perfect answer for the typical trawler skipper.
Many think they can run rapids and escape weather. Maybe. Once in a great while it’s possible but 95% of the time .. no.
Guys just like to “let-r-rip”. The’d like to go fast most of the time but that clearly burns too much fuel. Cars, boats and even motorcycles.

But compared to NA engines the turbo gives the option of having a smaller and lighter engine that has overall benefits for performance. Overall performance like boat handling and seaworthiness is a plus for most boats.
But the turbo engine is much like a dream come true. More power and less weight.

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And better efficiency which is why they were mandated(indirectly) in the first place.

rslifkin said:

To me, continuous duty means you can run it at WOT until it's time to change the oil. And do that again and again while still getting a good lifespan out of the engine.

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How do you square that with recreational engine manuals stating that WOT is to be used 10% or less of the running time? Change what WOT is?

silverback said:

The manual for my Yanmar 6LPA recomends that it be run up to high revs 5 times before letting idle for 5 minutes then shutting down. I feel like a teenager with his first motor bike but gotta assume the Yanmar engineers may just know a bit more than some whose opinions i have read. Certainly more than me.
To minimise my embarrassment i run hard at varying high revs for 15/30 minutes before throttling back to enter the marina. Thus demonstrating that i think i know more that the Yanmar blokes.

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Just run the engine where the turbo is contributing in the 80% load range and forget about all that revving prior to shutdown.

Big question for me is reliability and whether I can fix it myself when offshore. With a NA diesel as long as there’s fuel going through an injector, and air and compression it will run. I can replace low and high compression fuel pumps. I can replace hoses, injectors, fluids and such. I can’t see carrying an extra turbo but guess if I’m careful I can get it to run without turbo as a NA. However electronically controlled engines are well above my pay grade. For a long range trawler running outside helicopter range there’s still much to said for a Gardner or a Lugger. I’ve lived with a yanmar turbo for 7 years now and it was flawless. A great engine and easy to work on. Totally reliable. Hear bad stories about Volvo’s and parts availability once off the beaten track but that’s hearsay. But some how I’m still nervous about common rail and would prefer NA over turbo if you’re doing long distance ocean or off the grid cruising. Is this bias justified?

Hippocampus said:

Big question for me is reliability and whether I can fix it myself when offshore. With a NA diesel as long as there’s fuel going through an injector, and air and compression it will run. I can replace low and high compression fuel pumps. I can replace hoses, injectors, fluids and such. I can’t see carrying an extra turbo but guess if I’m careful I can get it to run without turbo as a NA. However electronically controlled engines are well above my pay grade. For a long range trawler running outside helicopter range there’s still much to said for a Gardner or a Lugger. I’ve lived with a yanmar turbo for 7 years now and it was flawless. A great engine and easy to work on. Totally reliable. Hear bad stories about Volvo’s and parts availability once off the beaten track but that’s hearsay. But some how I’m still nervous about common rail and would prefer NA over turbo if you’re doing long distance ocean or off the grid cruising. Is this bias justified?

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Unless you're looking at an older vessel for purchase, turbos for +120 hp are pretty much standard during the past 20 years or so.

Hippocampus said:

Big question for me is reliability and whether I can fix it myself when offshore.

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There you have the essential dichotomy here. Your plans are quite different than most here who will never make a real offshore passage beyond the occasional overnight run where you can limp a broken turbo to within a line-toss of engine repair.

The John Deere 6068D in various forms (Lugger, Nanni etc.) is used in KK and N older smaller sizes to my limited knowledge It’s NA.

rgano said:

How do you square that with recreational engine manuals stating that WOT is to be used 10% or less of the running time? Change what WOT is?

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That's because recreational engines are almost never continuous rated or even close to it. They're usually the lightest duty rating available, which means very little time at WOT (or anywhere above max continuous).

rslifkin said:

That's because recreational engines are almost never continuous rated or even close to it. They're usually the lightest duty rating available, which means very little time at WOT (or anywhere above max continuous).

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But are we not seeing some engines rated for both commercial and recreational applications? What is going on when that happens? Some fuel pump change or just lower WOT RPM spec to achieve commercial. I mean, I dunno, just asking.

rgano said:

But are we not seeing some engines rated for both commercial and recreational applications? What is going on when that happens? Some fuel pump change or just lower WOT RPM spec to achieve commercial. I mean, I dunno, just asking.

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Typically it's a difference in fueling curve and governed RPM. But on some engines, there are upgrades to the internal hard parts on the high output variants. As an example, the Cummins QSB 5.9 is one engine up to 380hp, then the 425, 440, and 480hp variants have some internal upgrades. The newer QSB 6.7 is the same engine across all power ratings, however, right up to 550hp.

Basically, on the lower output / higher duty cycle variants, they reduce max RPM a bit, reduce max power output and adjust the fueling curve to reach a point where it's durable enough in the expected usage.

Looking at the Cummins QSM11, they offer a bunch of ratings:

300hp / 1800 RPM - Continuous
355hp / 1800 RPM - Continuous
405hp / 1800 RPM - Continuous
405hp / 2100 RPM - Heavy Duty
455hp / 2100 RPM - Medium Continuous
610hp / 2300 RPM - Intermittent Duty
670hp / 2300 RPM - High Output
715hp / 2500 RPM - High Output

The Cummins rating descriptions can be found here: https://www.cummins.com/engines/marine-ratings

Thought in actual service boats going for heavy or continuous duty ratings are assumed to run only in a small range of rpm. Because of that a given prop is chosen in accordance to David Gerrs calculations or similar. Also a given gear ratio and transmission. Things are set up for the ideal sweet spot for that engine. My limited understanding is usually 70-80% max load. So for boats run at various speeds, loads, rpms it’s a more difficult situation. For full displacement hulls where those variables are less in play in some respects the calculations are easier.

menzies said:

Interesting conversation.

However it does beg the question; what is everyone's definition of continuous duty, and the difference in that definition between commercial and recreational?

Is there really any difference between the boat fishing the grand banks for a month at a time and the recreational boat running from Charleston to Bermuda when it comes to running continuous duty?

BTW my diesels are turbo'd but do not have aftercoolers.

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Duty cycle is a better term.

This maybe dumb and show my ignorance.
Would it be possible to have a common rail diesel mated to a variable pitch prop and variable geared transmission so that it always ran in its sweet spot. Engine rpm wouldn’t vary much nor load but torque and hp could vary. Would think a suitable black box getting info from from a variety of sensors( exhaust and coolant temp, torque, shaft and engine tach, throttle etc.) would make it possible. My experience was limited but have only owned boats with forward, neutral and reverse. Why are we limited to that.?

Hippocampus said:

This maybe dumb and show my ignorance.
Would it be possible to have a common rail diesel mated to a variable pitch prop and variable geared transmission so that it always ran in its sweet spot. Engine rpm wouldn’t vary much nor load but torque and hp could vary. Would think a suitable black box getting info from from a variety of sensors( exhaust and coolant temp, torque, shaft and engine tach, throttle etc.) would make it possible. My experience was limited but have only owned boats with forward, neutral and reverse. Why are we limited to that.?

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A variable pitch prop is a variable transmission, like having a variable tire diameter in a car.
The Nordhavn 56MS is one production boat that comes equipped with that system.

Variable pitch props are complex, expensive and heavy. Variable ratio gearboxes are difficult to make and even more difficult to make reliable. And the benefits of either or both is really quite small.

A modern diesel efficiency is really pretty flat from about 25% to 80% load, at normal rpm. Within that load and rpm ranges, efficiency only varies about 15-20% from best to worst.

So it just is not worth it to spend big money to optimize propulsion to the exact "sweet spot" of the engine. Getting it close is good enough.

Makes sense and good to know. But see high end RTW and high lat boats putting exhaust temp gauges with variable pitch props on them. These are small (~60’) boats with trans pacific range. The early Artnauticas were done this way. The Arksens ( 60-120’) can be ordered this way but also hybrid. Electric engines getting power from solar and or diesel. The diesels run at a pretty much set rpm and load. No transmission required for electric. Still get the point about transmissions. Just look at the difference between shaft HP and engine.

"Hear bad stories about Volvo’s and parts availability once off the beaten track but that’s hearsay."

Pick any Volvo diesel engine and call the local dealer and ask for a head gasket or a set of valves and springs.

A CPP (controllable pitch prop) lowers the parts count although a reduction gear is still usually needed , and some sort of clutch is a help.

I operated a Swedish motor sailor one summer and the only caution was to set the prop at neutral at a higher than slow idle before shut down.

When starting most cold diesels will come to life a bit over the slow RPM of a warm diesel.

A hand wheel controls the prop pitch , slowly, so its easier to jockey the throttle to obtain a flat pitch and not move if the power train does not contain a clutch .

The CPP prop system is available new , but the air police here and in Euroland have regulated the electronic engines into law.

If I were creating an ocean voyager , I would select the power style of a landing craft. Still OTS new.

Two engines on one shaft (big thick shaft) with center line prop . For power two identical engines would be selected tho one defueler for fast inshore and one smaller economical for off shore could also be fitted.

On a displacement boat identical engines would make most sense.


To me the simplest way to obtain a voyaging power boat would be an older cruiser , built with ocean scantlings and a simple NA engine. The noisemaker could be a get home.

Hippocampus said:

The John Deere 6068D in various forms (Lugger, Nanni etc.) is used in KK and N older smaller sizes to my limited knowledge It’s NA.

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Actually regarding this to thread it is 6068T.

Listings I’m looking at for older boats are 6068D which is NA.

NA?

menzies said:

NA?

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Naturally Aspirated, so non-turbo.