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Old 20 September 2015, 19:56   #1
zip
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What RPMs do you cruise your Cummins 6BT at?

Previous owner ran at 2200, and I kept it to the same on my one time out.

I have heard some people run higher.

How about you?
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Old 21 September 2015, 00:29   #2
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Look at the Cummins performance bulletins for the 6BT 210. They'll tell you where you can run at.

From Cummins:
"This power rating is intended for Intermittent use in variable load application where full power is limited to two (2) hours out of every eight (8) hours of
operation. Also, reduced power operation must be at or below 200 RPM of the maximum rated RPM. This rating is an ISO 3046 fuel stop power rating and is for applications that operate less than 1500 hours per year."

So, Cummins is officially saying you can run 2600 rpm (yes, the boat is propped to run 2750 rpm) for two (2) of every eight (8) and for the other six (6), you need to run 200 rpm below that - so, 2400 rpm. The previous owner was shooting for fuel efficiency!

http://www.sbmar.com/Engines/PDF/6BT...20Nov%2000.pdf
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Old 24 September 2015, 08:10   #3
zip
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Tom, as usual, you are a plethora of useful information.
In case clarification is needed, I don't doubt anything you say. I just remember you telling me about other individual(s), that basically run full throttle, and was interested in other's input.
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Old 24 September 2015, 08:55   #4
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From NCP's cummins data - it appears that the unit is what would be referred to as a "Leisure" engine as opposed to Commercial. As such, it is rated for limited hours per year and can only be run at max rpm for limited periods (expressed here as a % of run time). Typically, more HP will be squeezed out of a leisure engine than from a similar commercial block. It is normal practise to treat the recommended continuous max as the upper limits for cruising, reserving the absolute max revs (Flank Speed ) for the final leg of the run home in calm evening waters. This clears the exhaust/turbo and shows everyone on the dock how fast you normally travel
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Old 24 September 2015, 14:28   #5
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Quote:
Originally Posted by willk View Post
It appears that the unit is what would be referred to as a "Leisure" engine as opposed to Commercial. As such, it is rated for limited hours per year and can only be run at max rpm for limited periods (expressed here as a % of run time). Typically, more HP will be squeezed out of a leisure engine than from a similar commercial block.
Correct but very very few diesels are rated for continuous use. You're probably only going to find them in trawler type displacement hull - definitely not a rib!

Mechanical Cummins 5.9L blocks produce anywhere from 140 hp (non-turbo, non aftercooled) to 370hp (turbo charged and seawater aftercooled). The 180/210hp rating is turbo charged but doesn't have an aftercooler. Cummins newer 5.9L common rail engine (QSB) has been tweaked to make up to 480 hp.

The US Navy gets 99% of their Willards with the 180 hp rating which allows a little more WOT use (50% of the time allowed at WOT versus 25% of the time for the 210hp):
"Medium Continuous Rating: This power rating is intended for continuous use in variable load applications where full power is limited to six (6) hours out of every twelve (12) hours of operation. Also, reduced power operations must be at or below 200 RPM of the maximum rated RPM. This is an ISO 3046 Fuel Stop Power Rating and is for applications that operate 3,000 hours per year or less"
http://www.sbmar.com/Engines/PDF/6BT...20Nov%2000.pdf
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