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Old 12-14-2021, 10:17 AM   #41
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I agree, time matters more, so I normally run about 16 knts!
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Old 12-17-2021, 06:58 PM   #42
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[QUOTE=LovetoBoat;1060062]I am not trying to hijack the thread - I have a 500hp Cummins with a turbo charger. Those of you running at lower speeds - if you don't kick on the turbo charger - aren't you simulating a "blown turbo" and isn't that bad for the engine?


Turbos don't really "kick in", they are running all the time thanks to the exhaust stream running over their turbine wheel. The more robust the exhaust stream (more pedal to the metal) the faster the turbo spins, and the more the boost pressure. A properly engineered turbo installation will intrinsically provide the appropriate inlet air pressure boost appropriate to the the fuel being burnt when the propeller ratio is correct. The principal time you will damage a turbo is when you are over-propped and the engine can't get the RPM and thus commensurate air intake/throughput for the correct fuel/air ratio thus giving a "dirty burn" with lots of black smoke and carbon. Generally, if the turbo is properly matched to the engine and the propeller pitch and diameter are correct, the engine will run clean at all reasonable RPM's. They are not engineered to have one, and one only "sweet spot".
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Old 12-17-2021, 07:41 PM   #43
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I think we have 3 units. The engine, which is a constant, the gear box and the prop. The prop while very important, consider it a point for fine tuning the entire package. The engine mods, if drastic, might suggest the wrong engine was selected... IMO the only place mods would make sense is the gear box ratio. It can be designed for high speed, low speed or average, ignoring torque. Trawlers are pretty much designed for hull speed. Now given those parameters it is up to 'someone' in a higher pay grade to make the decisions on gearing recommendations. When all is done, the final tuning can be done with the prop.
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Old 12-17-2021, 09:49 PM   #44
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Originally Posted by OldDan1943 View Post
I think we have 3 units. The engine, which is a constant, the gear box and the prop. The prop while very important, consider it a point for fine tuning the entire package. The engine mods, if drastic, might suggest the wrong engine was selected... IMO the only place mods would make sense is the gear box ratio. It can be designed for high speed, low speed or average, ignoring torque. Trawlers are pretty much designed for hull speed. Now given those parameters it is up to 'someone' in a higher pay grade to make the decisions on gearing recommendations. When all is done, the final tuning can be done with the prop.

Don't forget that the gearing vs prop diameter balance will also be limited by what size prop fits under the boat.
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Old 12-18-2021, 06:37 AM   #45
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Don't forget that the gearing vs prop diameter balance will also be limited by what size prop fits under the boat.
true. I am open to criticism aka "you are nuts." and adjustment to my thesis
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Old 12-18-2021, 10:21 AM   #46
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Originally Posted by OldDan1943 View Post
I think we have 3 units. The engine, which is a constant, the gear box and the prop. The prop while very important, consider it a point for fine tuning the entire package. The engine mods, if drastic, might suggest the wrong engine was selected... IMO the only place mods would make sense is the gear box ratio. It can be designed for high speed, low speed or average, ignoring torque. Trawlers are pretty much designed for hull speed. Now given those parameters it is up to 'someone' in a higher pay grade to make the decisions on gearing recommendations. When all is done, the final tuning can be done with the prop.
Hi Old Dan,

i have the same cummins as your AT. I have been asking the Cummins factory about this low engine load for long periods of use.

My questions:

"Hi,

I have a Cummins 5.9 qsb marine engine 2009 and it reaches max rmp 3065 which is perfect my Nordic Tug 37.

I have read a lot of conflicting opinions on the engine to run at low rmp a long time, because the machine may damage the carbon and etc. Some say it's ok to run this type engine at low rmp if the coolant remains in the correct slot.

The time i run my engine is most often 850-1300 rpm since the boat is most economical in this rmp area and temperature is ok. Cummins runs fine and does not smoke any, exhaust pipe mouth environment does not show any black carbon.

What is the manufacturer's view of low load low rmp almost always, whether it is ok or damaging the engine?

It would be great to have an expert answer, all the web instead of rumors."

And Cummins answers:

"This is fine for our engines. It is not suggested to Idle (650-750rpm) for long periods. Generally speaking, you can idle for about 20 minutes or so at this range and be okay. If you plan to idle longer than 20 minutes or so it is suggested that you ramp up your RPM to about 800-1000. Working the engine under a light load/rpm is fine. This is not uncommon for some our engines (like Generators which normally work at 1800 RPM or less) and will not cause any undue harm.

Thank you for contacting Cummins.

Katelyn
Customer Care Representative

If we have misunderstood the information in your communication or you have additional questions please feel free to respond to our support staff by e-mailing support.engineparts@cummins.com or 1-866-CUMMINS (286-6467). If you are located outside of North America, you can reach us at 1-615-871-5500.

Visit us at www.cummins.com or www.cumminsengines.com "


The Cummins qsb 380 is a fine and reliable marine diesel, I have now used it for 2700 hours, running 95% of the time from 830-1100 rmp and the remaining 5% around 1400-2500rmp and the machine does not smoke or black carbon exhaust around the gel goat.

NBs
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Old 12-18-2021, 10:49 AM   #47
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Originally Posted by North Baltic sea View Post
Hi Old Dan,

i have the same cummins as your AT. I have been asking the Cummins factory about this low engine load for long periods of use.

My questions:

"Hi,

I have a Cummins 5.9 qsb marine engine 2009 and it reaches max rmp 3065 which is perfect my Nordic Tug 37.

I have read a lot of conflicting opinions on the engine to run at low rmp a long time, because the machine may damage the carbon and etc. Some say it's ok to run this type engine at low rmp if the coolant remains in the correct slot.

The time i run my engine is most often 850-1300 rpm since the boat is most economical in this rmp area and temperature is ok. Cummins runs fine and does not smoke any, exhaust pipe mouth environment does not show any black carbon.

What is the manufacturer's view of low load low rmp almost always, whether it is ok or damaging the engine?

It would be great to have an expert answer, all the web instead of rumors."

And Cummins answers:

"This is fine for our engines. It is not suggested to Idle (650-750rpm) for long periods. Generally speaking, you can idle for about 20 minutes or so at this range and be okay. If you plan to idle longer than 20 minutes or so it is suggested that you ramp up your RPM to about 800-1000. Working the engine under a light load/rpm is fine. This is not uncommon for some our engines (like Generators which normally work at 1800 RPM or less) and will not cause any undue harm.

Thank you for contacting Cummins.

Katelyn
Customer Care Representative

If we have misunderstood the information in your communication or you have additional questions please feel free to respond to our support staff by e-mailing support.engineparts@cummins.com or 1-866-CUMMINS (286-6467). If you are located outside of North America, you can reach us at 1-615-871-5500.

Visit us at www.cummins.com or www.cumminsengines.com "


The Cummins qsb 380 is a fine and reliable marine diesel, I have now used it for 2700 hours, running 95% of the time from 830-1100 rmp and the remaining 5% around 1400-2500rmp and the machine does not smoke or black carbon exhaust around the gel goat.

NBs
Thank you for that information
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Old 12-18-2021, 11:31 AM   #48
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Here is my analysis on our MS 390 done while on The Loop.

https://shellerina.com/2021/08/08/how-to-save-1000/

This typically adds one hour of cruising time to each day we are underway, but cuts our 1-year fuel consumption almost in half. (Obviously, sometimes we pick up the pace when fighting daylight into an unfamiliar port, which eats into that savings.)
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Old 12-18-2021, 12:59 PM   #49
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Hi Old Dan,

i have the same cummins as your AT. I have been asking the Cummins factory about this low engine load for long periods of use.

NBs
Maybe Cummins make a trolling valve for the engine
I do not know
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Old 12-18-2021, 01:03 PM   #50
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Mainship 34T with 6lypa cruising speed

For what its worth, I typically cruise my 2007 Mainship 34 at 1800 to conserve fuel. That will get me anywhere between 7 - 8 knots which is fine with me, and I get excellent fuel economy.
Every so often I take it up to full throttle for about 15 minutes to burn out the turbo - but only about every 15 or 20 hours.
The red line for me is around 3300. So the theory of 75% throttle 75% of the time would have you around 2400 but I don’t think this is very efficient on the Mainship hull.
Hope the posts are helpful for you.
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Old 12-18-2021, 01:24 PM   #51
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Maybe Cummins make a trolling valve for the engine
I do not know
Trolling valves are mated to the transmission, not the engine. Twin Disc in my NT 37 can have one. So can my friend's NT 42. No need unless you want to go really slow, like 1-2 knots.
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Old 12-18-2021, 02:39 PM   #52
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Sailinggod,
Red line? It should only be a matter of at what rpm can one operate at continuously at WOT.

75% load 75% of the time may be good or best for the engine. That was once thought of as the way to run a diesel engine but all the noise scares people. Also consider that 75% load will/can come at a wide variety of rpm. An over propped engine may achieve 75% load at a far slower engine speed while an underpropped system could run at much higher rpm and be at 75% load.

To say you run at ### rpm does not say much about fuel burn or economy unless one knows what your WOT rpm is and how it relates to your rated rpm.

IMO it’s load .. not rpm that wears out an engine.
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Old 12-19-2021, 04:47 PM   #53
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I agree, time matters more, so I normally run about 16 knts!
And, that can change! Before I retired, I was happy to exchange money for time, when I had more money than time.

Now, retired, I have a lot more time than money, so I do just the opposite!
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Old 12-20-2021, 07:37 AM   #54
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And, that can change! Before I retired, I was happy to exchange money for time, when I had more money than time.

Now, retired, I have a lot more time than money, so I do just the opposite!
You could be right, I'll know soon!
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