Reply
 
Thread Tools Search this Thread Display Modes
 
Old 05-11-2018, 01:05 PM   #1
Member
 
ghost0070's Avatar
 
City: Shelter Island
Vessel Name: Rosie
Vessel Model: American Tug 34
Join Date: Mar 2014
Posts: 21
Minimum Cruising RPM

Forgive me if this has been covered before. 2002 AT34 with the older 370hp Cummins. (6BTA 5.9 M3) It seems max cruise would be 2400 rpm, 80%. This is loud, very fast and not fuel efficient.
My bigger concern is the best minimum cruise. Currently I use 1600rpm, but I wonder if this is too low for good turbo health. I speed up once a day somewhere around 2200rpm.
Thoughts?
__________________
Advertisement

ghost0070 is offline   Reply With Quote
Old 05-11-2018, 01:09 PM   #2
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 21,943
If there is a positive boost you are fine.

The hassles with a turbo come when its just an exhaust obstruction , doing nothing for the boat.
__________________

FF is offline   Reply With Quote
Old 05-11-2018, 01:13 PM   #3
Member
 
ghost0070's Avatar
 
City: Shelter Island
Vessel Name: Rosie
Vessel Model: American Tug 34
Join Date: Mar 2014
Posts: 21
How do I know there is positive boost?
ghost0070 is offline   Reply With Quote
Old 05-11-2018, 01:32 PM   #4
Guru
 
dhays's Avatar
 
City: Gig Harbor
Vessel Name: Kinship
Vessel Model: North Pacific 43
Join Date: May 2015
Posts: 8,666
Quote:
Originally Posted by ghost0070 View Post
How do I know there is positive boost?
With a boost gauge. On my newer QSB that is information that the engine has. I never saw it until I upgraded my gauges.
__________________
Regards,

Dave
SPOT page
dhays is offline   Reply With Quote
Old 05-11-2018, 01:42 PM   #5
Technical Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 6,179
1600 is fine for a 6bta 370. Could go a good bit lower and still be fine.

My 6cta 450 has logged a couple thou hours at 950-1050. Sometimes I run on plane at 1800-2100, but don't like the fuel bill. Engine has about 3600hrs on it now and seems fine. Never been taken apart.
Ski in NC is offline   Reply With Quote
Old 05-11-2018, 01:46 PM   #6
Guru
 
MurrayM's Avatar
 
City: Kitimat, North Coast BC
Vessel Name: Badger
Vessel Model: 30' Sundowner Tug
Join Date: Jul 2012
Posts: 7,566
What does your owners or service manual say?

We run our Yanmar a bit past where the turbo gets a good whine on. The manuals give directions on what rpm to take the engine, and for how long, if running it below where the turbo is happy.
__________________
"The most interesting path between two points is not a straight line" MurrayM
MurrayM is offline   Reply With Quote
Old 05-11-2018, 02:46 PM   #7
Guru
 
BandB's Avatar
 
City: Fort Lauderdale. Florida, USA
Join Date: Jan 2014
Posts: 20,279
Quote:
Originally Posted by MurrayM View Post
What does your owners or service manual say?
+1
BandB is offline   Reply With Quote
Old 05-11-2018, 03:00 PM   #8
Member
 
ghost0070's Avatar
 
City: Shelter Island
Vessel Name: Rosie
Vessel Model: American Tug 34
Join Date: Mar 2014
Posts: 21
The manual speaks mostly about servicing. Not much about best operating practices.
ghost0070 is offline   Reply With Quote
Old 05-11-2018, 03:02 PM   #9
Guru
 
Ken E.'s Avatar
 
City: Bellingham WA
Vessel Name: Hatt Trick
Vessel Model: 45' Hatteras Convertible
Join Date: Nov 2016
Posts: 1,550
1600 is my 8 kt rpm for my Cummins 6bts. Many hundred hours up and down to Alaska with no ill effects.
Ken E. is offline   Reply With Quote
Old 05-11-2018, 06:16 PM   #10
Senior Member
 
BIG CAT's Avatar
 
City: Kiln,MS
Join Date: May 2016
Posts: 457
1600 is just fine. You're probably very close to peak torque at that rpm. The only concern could be if you noticed increased oil consumption if you ran too lightly loaded for extended periods of time. but it's easy to fix just run it at a higher load for 15 minutes +/- and it should clean it up. Then you can go back to normal.
BIG CAT is offline   Reply With Quote
Old 05-11-2018, 08:06 PM   #11
Guru
 
RCook's Avatar


 
City: Holladay, UT
Vessel Name: Dream Catcher
Vessel Model: Nordic Tug 37-065
Join Date: Oct 2007
Posts: 730
Our 37 Nordic Tug cruises with its 6BTA 5.9 M3 mostly at 1300-1400. It seems to be a very happy engine. 1600 hours on it in the last two summers.

Our previous boat's 260 hp Volvo KAD44P cruised mostly at 1300-1400 too, working just hard enough to keep operating temps close to the normal range. We put 6500 hours on it before we sold it.

I think Cummins guru Tony Athens of Seaboard would say not to worry.
__________________
Richard Cook
Dream Catcher (Nordic Tug 37-065) Poulsbo WA
Previously: New Moon (Bounty 257), C-Dory 22 Cruiser
"Cruising in a Big Way"
RCook is offline   Reply With Quote
Old 05-11-2018, 08:34 PM   #12
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,114
I thought this forum established that lube oil temp was the prefered way to tell if an engine was loaded high enough to gaurd against varnish buildup and whatever else happens at temps too low.
Seems to me it was 170 degrees. And an EGT gauge in the exhaust is a fairly good way of telling if an engine is working hard enough.

One thing’s for sure. It’s not an rpm issue or problem but a matter of enough heat.

If there’s such a thing as a “happy engine” the road to this happeness is through maintaining or exceeding minimal operating oil and exhaust gas temp or/and not exceeding maximums.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 05-11-2018, 08:37 PM   #13
Guru
 
dhays's Avatar
 
City: Gig Harbor
Vessel Name: Kinship
Vessel Model: North Pacific 43
Join Date: May 2015
Posts: 8,666
Minimum Cruising RPM

Quote:
Originally Posted by Nomad Willy View Post
I thought this forum established that lube oil temp was the prefered way to tell if an engine was loaded high enough to gaurd against varnish buildup and whatever else happens at temps too low.
Seems to me it was 170 degrees. And an EGT gauge in the exhaust is a fairly good way of telling if an engine is working hard enough.

One thing’s for sure. It’s not an rpm issue or problem but a matter of enough heat.


I typically run my QSB 5.9 at 1,400 to 1,500 rpm. Usually towards the lower end. My coolant temp stabilizes at 172 degrees.
__________________
Regards,

Dave
SPOT page
dhays is offline   Reply With Quote
Old 05-11-2018, 09:09 PM   #14
Guru
 
Rebel112r's Avatar
 
City: Birch bay wa
Vessel Name: Rogue
Vessel Model: North Pacific 42
Join Date: Feb 2013
Posts: 650
Quote:
Originally Posted by RCook View Post
Our 37 Nordic Tug cruises with its 6BTA 5.9 M3 mostly at 1300-1400. It seems to be a very happy engine. 1600 hours on it in the last two summers.

Our previous boat's 260 hp Volvo KAD44P cruised mostly at 1300-1400 too, working just hard enough to keep operating temps close to the normal range. We put 6500 hours on it before we sold it.

I think Cummins guru Tony Athens of Seaboard would say not to worry.


Richard are you in Booker also with Salty
Rebel112r is offline   Reply With Quote
Old 05-11-2018, 09:30 PM   #15
Guru
 
Simi 60's Avatar
 
City: Queensland
Vessel Model: Milkraft 60 converted timber prawn trawler
Join Date: Jul 2016
Posts: 3,424
1150rpm gives us 7.2ish knots.
Water sits at 80c or 176f
Oil temp sits at 75c or 167f

Cummins nta855m
Simi 60 is offline   Reply With Quote
Old 05-12-2018, 07:13 AM   #16
Guru
 
caltexflanc's Avatar
 
City: North Carolina for now
Join Date: Aug 2011
Posts: 6,562
Speaking of Tony Athens, here is one of his takes on the subject:

Quote:
As for life expectancy on a typical modern high speed diesel engine (probably an old one too), when run at 10-50 % of its rated hp, you’ll get longer life (substantially in many cases) when measured in engine hours, everything else being equal..As a general statement, Detroit diesels of WWII design built their “long life” reputation on running slow..Most of my work in the last few years has been replacing Detroit 2-strokes in commercial vessels with Cummins C series engines that are set up to run at approx 30-40% of their rated hp when cruising for long/extended periods. This WILL allow these engines to accumulate approx 20,000+ hrs of engine time before rebuild due to ring/cylinder, head and bearing wear.. The Cummins 6BT 210 is a 10,000 hr+ engine in an application that lets the engine cruise at about 50-60% of rated HP with the remainder of the hours between idle and 50% of load.. I’m also making the assumption that the engine doesn’t fail due to maintenance/installation problems. I personally own a 4BT (2 cylinders less than a 6BT) that had a “top- end” at 13000 hrs and is now approaching 30,000 total hrs and still has all of the original base engine parts in it.. By far, most of its hours have accumulated at well under 50% of its rated HP.

To me, the easiest way to gage whether slow speed running is detrimental over years and years of operation is to look at commercial fishing vessels with older designed engines from Detroit, Cat, Cummins, etc… Revisiting the “Detroit” mystique again, its longevity was built on engines rated to run at 1900-2100 RPM and above, but could only last for 30+ yrs when operated continuously at 1100-1600 RPM (again, well under 50% of rated HP)..These same engines in a “crew” boat used in the off-shore oil industry, would go through “top-ends” (or worse) just about yearly when run at close to their governor settings..The longest-lived engines that I’ve been involved with (hrs and yrs wise), have been engines in commercial or recreational trawler type applications run at 50% of rated HP or less..Yes, there are many other parts of the equation that leads to the life of a diesel engine, but I know from experience that running them slow (i.e. cruising for days on end at hull speeds or less) is NOT a cause for concern. But some obvious things to watch out for (when running slow) are being sure your coolant temp stays up to spec. and watching for any signs of wet stacking or slobbering..Some Detroits seem to do this, but I think it’s more of the general condition of that particular engine and is sometimes related to the design of the exhaust system.. A few minutes a day at higher cruise HP levels should be all that is necessary to clean things up should it be needed..
__________________
George

"There's the Right Way, the Wrong Way, and what some guy says he's gotten away with"
caltexflanc is offline   Reply With Quote
Old 05-12-2018, 08:31 AM   #17
Guru
 
City: gulf coast
Join Date: Jun 2014
Posts: 3,441
You want to keep the bow down not worry about RPMs At low RPMs that engine will outlive your grandkids. If the coolant temp is too low use higher temp thermostats. Lower temp stats will raise low load temps but not affect full load temps.
bayview is offline   Reply With Quote
Old 05-12-2018, 09:24 AM   #18
Guru
 
City: Carefree, Arizona
Vessel Name: sunchaser V
Vessel Model: DeFever 48
Join Date: Apr 2008
Posts: 9,253
Quote:
Originally Posted by Nomad Willy View Post
I thought this forum established that lube oil temp was the prefered way to tell if an engine was loaded high enough to gaurd against varnish buildup and whatever else happens at temps too low.
Seems to me it was 170 degrees. And an EGT gauge in the exhaust is a fairly good way of telling if an engine is working hard enough.

One thing’s for sure. It’s not an rpm issue or problem but a matter of enough heat.

If there’s such a thing as a “happy engine” the road to this happeness is through maintaining or exceeding minimal operating oil and exhaust gas temp or/and not exceeding maximums.
Good points Eric. Many marinization builders include a coolant to oil heat exchanger to insure light loading oil temperatures stay in the minimum range of coolant temperatures, say 175F. And lightly loaded is common as noted by other posters.
sunchaser is offline   Reply With Quote
Old 05-12-2018, 10:30 AM   #19
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,114
Ten years ago a PM guru (Steve Antonio) said to run at 70% load 70% of the time.

Starting to appear now it dosn't matter what one does???

I run my engine at 50%. Much more and it's a bit too noisy over time. And I'm a believer in keeping the oil temp up. So it's 50% for me. Of load that is .. not rpm as many seem to think.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 05-12-2018, 10:52 AM   #20
Technical Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 6,179
The Cummins engines being discussed have an oil to coolant heat exchanger (oil cooler) so temps tend to stay in pretty narrow band unlike the sea water oil cooled brands (Volvo, Yanmar, Lehman). At low load the Cummins oil temp will be near coolant temp, at high load typically gets to about 20-30F higher than coolant temp. No concerns there.
__________________

Ski in NC is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



» Trawler Port Captains
Port Captains are TF volunteers who can serve as local guides or assist with local arrangements and information. Search below to locate Port Captains near your destination. To learn more about this program read here: TF Port Captain Program





All times are GMT -5. The time now is 04:35 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012
×