Trawler speeds

[Irie308]

Someone recently posted a question on going at slower speeds for an extended period of time. Rather than hijack their thread i figured i'd post here since our DB is new to us and we are new to diesels as well. Aside from the relaxation that occurs at 8-10kts. It would be nice to get some feedback from those that cruise at slower speeds for an extended period of time and the steps you take to ensure you are caring for your motors (when do you open them up, engine hours etc). I've read up on ours via the 6 CTA thread as well as Cummins documentation for continuous loads but it really doesn't go into running them at slower speeds. I've also read up on the sweet spot for trawling on our boat (1200 rpm) and the fuel curves etc. I recently spoke with a Cummings tech who did work on our motors and he advised that they are much happier being run at 80% of WOT. Conversely we know those who run these motors at lower rpms for years without issues. Would be nice to get a feel for how many out there run at trawler speeds, when do you jump up on plane to ensure you are exercising your motors etc. For us if we're in no rush and the sea state is favorable we relax and trawl but when the trip is over and we want to get back home in quick time we jump up to 22-2300 rpms.

 

[Ididntdoit]

Talk to Alex - I know he's run quite a bit at those speeds.....

 

[my3sons]

We run at trawler speeds quite a bit. Our motors have 2500 hrs on them, We are the second owners and have put on 2100 of those. I am guessing that 1500 to 1600 of our 2100 have been run between 1000 and 1150 rpm. I have installed egt gauges, and when running slow speeds, run hard enough to build egt's to around 500 degrees, on our boat, that's 1100 rpm, giving about 8 kts.
I have always sent out the oil for analysis, and there has been no difference in oil that had been in service during a time of extensive slow speed cruising and that of times when we ran a lot at 2250 -2300 rpm. The oil has shown that metals had been steadily dropping over the years until around 1800 hours, where it has leveled off, counts are well below universal averages for these motors, and fuel dilution always comes back at trace to less than .5%.
IR readings on the oil filters show well into the 170's at this speed. (160 thermostats)
Aftercooler maintenance has shown no excessive air side buildup.
If you are not familiar with egt, as an example, 850 rpm produces egt's so low that it can not be read on the gauges that begin at 300 degrees, so don't misunderstand, you can't go idling around for long periods of time or problems in all likelihood will not be far behind.
Some say that when running slow for several hours, it is a good idea to run them up to cruise for 15 or 20 minutes. This certainly won't hurt anything, but IMO, slow is slow enough that egt has not got off the peg, 1150 is fine to run for extended hours and several days or even longer except that if I find myself in a situation where we may have run at 1100/1150 for 20 - 30, maybe 40 hours straight, I make a point to get up and go at the first opportunity just to check the turbo boost against known background numbers, remember that the turbo doesn't come in until around 1400 rpm.
This year when we returned home from Fl/Bahamas, there was a flooding and high water condition on the Erie Canal. The Canal Corporation had opened and closed the canal on and off dependent on flow volumes, and when it was open and we were allowed to move, it was mandatory no wake because of soil erosion concerns. (although the canal is mostly no wake all the time for us because of boat size) We traveled approximately 350 miles over an 8 day span at never more than 800 rpm with a lot of idling (34 locks). That's a case when we run fast cruise first chance we get for a half hour or so with a quick run up to WOT to see our 2700 to 2725 rpm.

 

[Irie308]

Great info!