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Old 08-21-2020, 06:36 PM   #101
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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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Old 08-21-2020, 06:57 PM   #102
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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?
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.
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Old 08-21-2020, 07:25 PM   #103
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Big question for me is reliability and whether I can fix it myself when offshore.
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.
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Old 08-21-2020, 07:53 PM   #104
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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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Old 08-22-2020, 07:33 AM   #105
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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?

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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Old 08-22-2020, 07:50 AM   #106
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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).
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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Old 08-22-2020, 08:13 AM   #107
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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.
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
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Old 08-22-2020, 09:52 AM   #108
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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.
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Old 08-22-2020, 10:10 AM   #109
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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.
Duty cycle is a better term.
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Old 08-22-2020, 10:27 AM   #110
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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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Old 08-22-2020, 11:23 AM   #111
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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.?
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.
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Old 08-22-2020, 11:30 AM   #112
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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.
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Old 08-22-2020, 12:36 PM   #113
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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.
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Old 08-23-2020, 06:45 AM   #114
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"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.
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Old 08-23-2020, 08:25 AM   #115
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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.
Actually regarding this to thread it is 6068T.
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Old 08-23-2020, 08:28 AM   #116
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Listings I’m looking at for older boats are 6068D which is NA.
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Old 08-23-2020, 08:31 AM   #117
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NA?
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Old 08-23-2020, 08:34 AM   #118
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NA?

Naturally Aspirated, so non-turbo.
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