Diesel operation, how do you run them?

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pdecat

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In another thread ranger said
quote:
We were told in Diesel Class that most diesels in pleasure craft should be operated in the range of 75-80% of their rating, or 200 RPMs off the top, or 400 RPMs off the top... or somewhere in between there... with those variances being based on engine manufacturer, engine type (turbo versus natural), specific engine, etc.
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Ranger: I wasn't there and didn't hear exactly what was said but it was probably more along the lines of “high cruise should be in the range stated not above that level“. Nothing said would have required running at those levels just not above those levels.
 
I think you should be able to obtain that range however I only push my 4-53 along at around 1300 to 1400 rpm's. The biggest issue is to keep a load on....
 
I have twin detroit 8.2T's. Being older engines, I run them rb2@gr5t 65% (1900-2000rpm). fuel flows are good, no smoking, missing, etc. As long as they seem happy; so am I
 
Cummin "B" series engines (210 to 370hp) are rated for a minimum rpm at WOT and a recommended cruise maximum of 200 rpm less than rated for excellent durability.

The minimum engine speed would be that which allows the engine to maintain proper operating temperature.
 
Bob: I agree with the specs but not your conclusion. An engine that was overloaded, couldn’t reach a rated minimum rpm, would want to run too hot internally at that speed.
 
Cummins QSC's 200 off the max RPM all day everyday !

Rob
 
quote:
Originally posted by Robski97

Cummins QSC's 200 off the max RPM all day everyday !

Rob

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that's were i ran my C's at all the time & had no issue with the fuel burn.
I run my Cat's most of the time at 2000RPM, 300 off the top and sometimes at the 2100 if i want to grab 3+ knots more but pay the price for an extra 10 more GPH
 
I run my Cummins 8.3 l at 1200 rpm for slow cruise and 2200 rpm for fast cruise. 2600+ wot
 
Detroit 6-71 TAs. 2550rpm WOT, I run 2200rpm for a cruise of 23kts.
 
quote:
Originally posted by pdecat

do any of you run slow for long periods??

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Sure
Going threw the harbor to & from the slip ;-)

Sometimes running up/down rivers like the CT, Mystic, Thames etc to enjoy the view- sometimes not, as their often flat as glass and it's fun to crank it up a bit!
 
quote:
Originally posted by pdecat

do any of you run slow for long periods??

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When we are cruising, I typically run my 8v92ti Detroits in the 1200-1400 range most of the day (2350 WOT) to attain 8-9 knots and stay below hull speed. This gets them up to within the manufacturer's recommended operating temperature and oil pressure range. Towards the end of the day I will run up about 2100 for awhile per the recommendation of two mechanics I trust. This has worked out great for over 4 years now, and the engines check out fine. Now that we are not full time cruisers. using the boat year around on a regular basis and block heaters during the cold months also seems to help.

Modern electronic engines seem to be far more tolerant of slow speed for extended periods of time, and not subject to "wet stacking", which is why the recommendation on mine to "blow them out" for awhile after a day of slow cruising.
 
I think you will find many trawler owners run well below max RPM. We cruise our Mainship w/ single CAT 3116 at 1600 rpm all day long. 1,800 hours on her with zero problems.
 
Most older trawlers can't get to 10 knots. They can run at 1800 rpm and just get to 8 or 9 knots due to the low HP.

Walter is talking about a planing hull with a lot higher HP.
 
quote:
Originally posted by pdecat

Ranger: I wasn’t there and didn’t hear exactly what was said but it was probably more along the lines of “high cruise should be in the range stated not above that level“. Nothing said would have required running at those levels just not above those levels.

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Yep, you're correct. The intent was that recommended cruise ranges are stated in slightly all-over-the-map language, but the gist is sorta the same. FWIW and as a single example, the QSC guidance is to cruise at not more than 200 off the top (similar language to rbmitchell's note about QSBs). Not that you MUST, only that you must not exceed except for X hours out of every Y running time.

I'm good with our putzing along at sight-seeing RPMs, as long as engine temp and oil pressure are within the normal operating range... and as long as sea states don't make that too uncomfortable for our hull form.

-Chris
 
If I wanted to run at 10 knots, I would buy a sailboat, actually, I would buy a gun and shoot myself :)
 
quote:
Originally posted by walterv

If I wanted to run at 10 knots, I would buy a sailboat, actually, I would buy a gun and shoot myself :)

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Now that was damn funny!!!
 
Ranger: Thanks for clearing that up. Many folks seem to think they must run at 200 off the top as if nothing lower is allowed for some reason.
 
quote:
Originally posted by walterv

If I wanted to run at 10 knots, I would buy a sailboat, actually, I would buy a gun and shoot myself :)

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now that's funny..darn near spit my coffee all over my laptop.
 
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