Am I at the right cruising speed

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I have two of these engines. They will be happy running at that RPM all day. You many not be as happy with the fuel economy as you would be at lower speeds.
 
IF you have 2 engines you gotta sync them....
 
OldDan1943 said:
...I added a swim platform to my N46 and presto, I was driving a 49 ft boat...
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I really want to be eligible to join the Boat International owners club so I can hang out with outrageously rich people who wear white pants and navy blue blazers and ascots, but the eligibility for that club is a boat that's 24 meters or 78.7 feet. Somehow I need to figure out how to extend my 40' LOA by 38.7 more feet. Has crossed my mind to paint a big red 36" diameter "H" inside a circle on my bow and then use a drone to take what looks like high altitude shot of my helipad, but they'll probably see through it.
 
I got a little sideways with the harbor master in our marina over my length. Like many I have a so called 34 CHB, a Puget Trawler. But from end to end with pulpit and swim step and the dinghy against the transom I was too long for my slip at 37', rear end into the fairway which for a time at least was a huge problem for some reason.
Not so much now but I moved into a longer, more expensive slip so I could avoid the issue altogether.
The 34 CHB is almost 34 on the waterline.
 
kthoennes said:
I really want to be eligible to join the Boat International owners club so I can hang out with outrageously rich people who wear white pants and navy blue blazers and ascots, but the eligibility for that club is a boat that's 24 meters or 78.7 feet. Somehow I need to figure out how to extend my 40' LOA by 38.7 more feet. Has crossed my mind to paint a big red 36" diameter "H" inside a circle on my bow and then use a drone to take what looks like high altitude shot of my helipad, but they'll probably see through it.
Click to expand...

I have a very difficult impressing me.
I sure dont want to waste my life impressing others.

I'm finished, back to the program already in progress.
 
rslifkin said:
Planing will be more efficient than plowing. But if you compare planing to an efficient slow cruise of say 6.5 kts, slow will produce better mpg. On my boat, mpg at 6.5 - 7 kts is more than double what it gets on plane at 17 - 18.
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Of course that is true. My reply started around the post about a 34' boat running at 10 knots. My guess, that is not very effcient and not worth the extra fuel to go a little faster than hull speed.
 
78puget-trawler said:
I got a little sideways with the harbor master in our marina over my length. Like many I have a so called 34 CHB, a Puget Trawler. But from end to end with pulpit and swim step and the dinghy against the transom I was too long for my slip at 37', rear end into the fairway which for a time at least was a huge problem for some reason.
Not so much now but I moved into a longer, more expensive slip so I could avoid the issue altogether.
The 34 CHB is almost 34 on the waterline.
Click to expand...

Whether we like it or not, marinas are only interested in LOA and clearly state that includes any projections including swim platforms and bow pulpits. Many of us subtract those when we can away with it, but don't blame the harbor master if your 34 footer is really 38' or more.
 
backinblue said:
Of course that is true. My reply started around the post about a 34' boat running at 10 knots. My guess, that is not very effcient and not worth the extra fuel to go a little faster than hull speed.
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That sort of depends on the next refueling dock and the credit limit on your bank card
 
OldDan1943 said:
That sort of depends on the next refueling dock and the credit limit on your bank card
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True. If you want to double your fuel cost to gain 2 knots, you are free to do so.
 
tiltrider1 said:
Certainly the boat is happy cruising at 2200 RPMs. Is it fuel efficient? No! What is more important to you, fuel efficiency or time? I am not very sensitive to being fuel efficient so I would be happy with what you are doing. The boat probably rides better at 8.5kts than it would at 7kts.
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*1:thumb::oldman:
My old single diesel 32 Halvorsen's sweet spot was 2000 & 8.4 knots.
 

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I agree, time matters more, so I normally run about 16 knts!
 
LovetoBoat said:
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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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.
 
OldDan1943 said:
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.
Click to expand...


Don't forget that the gearing vs prop diameter balance will also be limited by what size prop fits under the boat.
 
rslifkin said:
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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true. I am open to criticism aka "you are nuts." and adjustment to my thesis
 
OldDan1943 said:
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.
Click to expand...

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
 
North Baltic sea said:
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
Click to expand...

Thank you for that information
 
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.)
 
North Baltic sea said:
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
Click to expand...

Maybe Cummins make a trolling valve for the engine
I do not know
 
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.
Cheers
SG
 
OldDan1943 said:
Maybe Cummins make a trolling valve for the engine
I do not know
Click to expand...
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.
 
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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backinblue said:
I agree, time matters more, so I normally run about 16 knts!
Click to expand...

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! :D
 
Group9 said:
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! :D
Click to expand...

You could be right, I'll know soon!
 
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