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Old 06-09-2017, 03:31 PM   #1
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Trawler speed & turbo life

I have a pair of 6-cyl Yanmar turbo diesels. At 1000 rpm's we cruise comfortably at 10 kts @ 10gal/hr (the holy grail of cruising). At this rpm our turbos are idle.

Question: I have heard that running at low rpm's for extended periods of time without engaging the turbos can have adverse effects.

If this is true, is there an optimum protocol (e.g. some time at 1500, 2000, 2500, etc.)?

Thanks,

Lou
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Old 06-09-2017, 03:42 PM   #2
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10gal or 38L / hour is the holy grail?

That's 23 litres/hour more than we burn on our 60ft 70 tonner doing 1250rpm @ 8 knots
We are experimenting @ 7 knots and 1150 as I have read that may get us closer to 10 L or 2.5 gal/hour, which I considered the holy grail. :-)

As to your question, many believe that as long as oil is to temp, approx 10c above water temp, then you are OK.

Some info below.

Low Speed Running & “Break-In” of Marine Diesels
https://www.sbmar.com/articles/low-s...arine-diesels/

Cummins Diesel Twin 500hp QSC8.3 Permanent Slow Speed
http://www.cruisersforum.com/forums/...eed-67573.html
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Old 06-09-2017, 03:55 PM   #3
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10kts at 10gph? What size boat and what engines? Unless a very large boat, that is not an efficient speed.

Regarding turbos, you can run slow all day, even well below 1000. Just once a day, run it hard (like 2000 or so) for 15min. That will clean it out.
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Old 06-09-2017, 04:00 PM   #4
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Wow!! 4-236 Perkins, 28 foot boat- 1600 RPM=1.75 gallon per hour, 7 knot average.
I need a larger boat!!!

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Old 06-09-2017, 04:18 PM   #5
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Thanks for the good feedback regarding the turbos.

Regarding the holy grail - I forgot I was posting in a trawler forum. To Simi60: we can run @ 8kts on 4-5 gal/hr too. But, for us, 10kts seems to be the sweet spot. We also like the option of being able to run 22kts when we want to get somewhere. Of course we don't the range that y'all have.

Thanks again for the feedback!
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Old 06-09-2017, 05:40 PM   #6
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Information regarding that can be found in either the operators manual or the service manual for your engines. For our Yanmar there's a recommendation to run it at a fairly high rpm (can't remember right now) for a few minutes after running at low rpm or at idle for a certain length of time. A parts catalogue is also a good idea.
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Old 06-09-2017, 07:54 PM   #7
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I vote for 10kts, too. My economic speed is 6-7kts, but an old guy can figure dead reckoning in his head easier at 10.
I have 80 tons, 83x17 and do about 8.5 gallons an hour at 10kts with Detroit Diesels.
I've run diesels from 20 hp to many thousands. The turbo always turns a little. Running below boost greatly increases the life of the engine, especially the sleeves, rings and valves. The first time you use high power the turbo will blow out any build up, usually in a few seconds.
The killer for turbos is dirty oil. If the line going to the turbo bearing gets partially blocked by sludge, the seal gets too hot and fails, then the bearing fails. Oil is the coolant for your turbo. When I run engines at high power, I usually rebuild the turbo at about half life and never lost a turbo. But I rebuilt a number of turbo equipped engines that didn't get regular oil changes and replaced a number of turbos for people that run their engines hard.
It's really easy and cheap to put new seals and bearings in a still working turbo. Usually less than $100. But a new small turbo is $1000 or more.
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Old 06-09-2017, 09:41 PM   #8
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Another big turbo killer is bad exhaust geometry where sea water incursion is evident when the turbo is pulled. This is most common on high powered engines installed below floors with little overhead room for high risers. Trawlers with walk in engine rooms rarely have this problem since there is plenty of headroom to go up with exhaust before down or might even be dry stacked.
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Old 06-09-2017, 11:33 PM   #9
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What I find interesting is the speed you are choosing to run.

I can run my boat at 10 knots and get like you about 1 nmpg.

If I reduce my speed by just one knot my fuel economy goes up 50% to 1.5 nmpg. My boat also "sounds" happier to me. My level at the helm shows a flat running angle, and my EGT's go down by 200 degrees.

So... I choose not to run at 10 knots. If 9 knots is not fast enough(rarely the case) , or if the sea state bounces us around too much(more often the case), we ramp up to a 14 knot cruise speed at 2400 rpm.

Last week for the first time I wan at 2800 rpm and 19 knots for an hour running from a thunderstorm, but that was a one time thing.
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Old 06-10-2017, 01:16 AM   #10
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Ever higher anti-pollution regulations are a major drive for turbos. Have no need for them, and thankfully, purchased a boat not needing them.
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Old 06-10-2017, 04:39 AM   #11
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Everything is a regulation in California.
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Old 06-10-2017, 05:18 AM   #12
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Quote:
Originally Posted by lwaugaman View Post
I have a pair of 6-cyl Yanmar turbo diesels. At 1000 rpm's we cruise comfortably at 10 kts @ 10gal/hr (the holy grail of cruising). At this rpm our turbos are idle.

Question: I have heard that running at low rpm's for extended periods of time without engaging the turbos can have adverse effects.

If this is true, is there an optimum protocol (e.g. some time at 1500, 2000, 2500, etc.)?

Thanks,

Lou
Quote:
Originally Posted by Ski in NC View Post
10kts at 10gph? What size boat and what engines? Unless a very large boat, that is not an efficient speed.

Regarding turbos, you can run slow all day, even well below 1000. Just once a day, run it hard (like 2000 or so) for 15min. That will clean it out.
Aaaaahh, clean what out exactly..? My car's turbo is at idle most of my travelling, as with all turbo road vehicles, unless racing or being driven hard, and therefore very uneconomically. No problems with needing a clean out. The turbo is in the exhaust stream, carbon is being burned out all the time, unless the mixture is horribly wrong and rich. I know what you just advised in the traditional wisdom, but have often wondered just how scientifically accurate it is..?
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Old 06-10-2017, 05:36 AM   #13
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The problem as noted is the turbo oil supply.

The hassle comes when the turbo is run hard and then the engine is shut down too quickly.

The oil in the turbo feed gets hot enough to cook , leaving deposits in the feed line.

3 or 4 min is usually enough for the turbo housing to cool to below oil cooking temps .

A turbo not making boost is simply an obstruction , no help to fuel consumption or power.
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Old 06-10-2017, 05:54 AM   #14
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Quote:
Originally Posted by lwaugaman View Post
I have a pair of 6-cyl Yanmar turbo diesels. At 1000 rpm's we cruise comfortably at 10 kts @ 10gal/hr (the holy grail of cruising). At this rpm our turbos are idle.

Question: I have heard that running at low rpm's for extended periods of time without engaging the turbos can have adverse effects.

If this is true, is there an optimum protocol (e.g. some time at 1500, 2000, 2500, etc.)?

Thanks,

Lou
A fellow TF member, Codger, has a 42' OA with twin Yanmars. He is an experienced boater and can provide some information and/or steer you to the right people to get a definitive answer. He too is located in San Diego.
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Old 06-10-2017, 09:09 AM   #15
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Everything is a regulation in California.
Yep. Another good reason to move to Texas. Or Florida.
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Old 06-10-2017, 09:27 AM   #16
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Quote:
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Aaaaahh, clean what out exactly..? My car's turbo is at idle most of my travelling, as with all turbo road vehicles, unless racing or being driven hard, and therefore very uneconomically. No problems with needing a clean out. The turbo is in the exhaust stream, carbon is being burned out all the time, unless the mixture is horribly wrong and rich. I know what you just advised in the traditional wisdom, but have often wondered just how scientifically accurate it is..?
You probably are right. You really don't need to run it up at all. But the cost of the run up is minimal, and what smoke you see will tell you if there is any cleaning going on. No smoke, it was clean. Lots of smoke, you cleaned it.

My Cummins 450 if I run hull speed a few days in a row when I do power it up, will puke a good bit of smoke for several seconds. Oil/soot/sludge residue in exhaust manifold and turbo.

I too drive a turbo diesel car. If I putt-putt around town for a month, then go on a full power pull up a bridge to rated rpm, it blows out a good cloud of soot. If I do the same again, no soot. I had cleaned it out. Italian tuneup. Highly recommended. unless it blows the engine!!!
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Old 06-10-2017, 10:27 AM   #17
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Some marine after coolers build up a lot of gunk under sustained low load conditions. CCV systems like mine re-introduce vapors back into the charge air intake side resulting in a small pooling of oil in the AC low spots at low loads. At higher RPMs those residual AC oils get stirred up and sucked into engine, burning off as designed.

Autos and trucks do not have marine after coolers, this being the primary difference. Marine after coolers (especially raw water) can be the significant boat engine repair hassle and cost, is for me. Turbos are easy to keep going, add an AC and things get busier.
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Old 06-10-2017, 11:43 AM   #18
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Yep. Another good reason to move to Texas. Or Florida.
But then you have to live in Texas or Florida!
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Old 06-10-2017, 02:53 PM   #19
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But then you have to live in Texas or Florida!

Yes indeed, and a grand thing it is.
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Old 06-10-2017, 08:48 PM   #20
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Our 330 hp Cummins We run at
14 knots, 2400 RPM and only burn 1.75 gallons an hour.
Then I wake up and realize it was only a dream.
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