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Old 09-15-2020, 10:51 PM   #21
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Trouble comes from trawlers liking hull speeds and turbos needing to spool up and clean out. My mechanic says run the Cummins hard for 10 minutes before returning to the berth.
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Old 09-15-2020, 11:11 PM   #22
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Our manual for our little 30hp non-turbo Yanmar, a 3YM30, provides the same instruction. It is our wing or auxiliary or get home engine. We run it when arriving to a marina, and when loafing along at a few knots, so it gets exercise. I follow the guidance before shutting down.
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Old 09-16-2020, 06:51 AM   #23
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The usual reason for slow running a turbo before shut down is to lower the turbo temperature enough so the oil in the bearings will be cool enough not to coke.
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Old 09-16-2020, 09:37 AM   #24
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Read this by Steve: https://stevedmarineconsulting.com/t...under-loading/
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Old 09-16-2020, 09:48 AM   #25
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I have been in the habit of running my motors up to full throttle every 40-50 hours of run time. I normally cruise at 1400-1500 rpm. The last time I did this at various higher rpms for about 20 minutes. No black smoke, but my fuel burn went from 6gph to over 8gph for the total between fill ups! Don't think I will do more than a 2-3 minute run up in the future. BTW, I have twin Cat 3208TAs.

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Old 09-16-2020, 10:16 AM   #26
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I would not put too much faith into that part of the manual. In my past engr career I wrote parts of manuals for various machinery (including large diesel gensets) and it was amazing how little oversight there was over what I wrote. Sometimes the task was given to me as it was boring and I was the junior guy. Sometimes I had to do a revision and in reading it there was stuff that did not make great sense, but to make the task simpler I would leave that bit alone. And then you have the Yanmar manual that was clearly translated from Japanese, and I have had many examples where I am an certain the translation was not well done.

My general rules for care and feeding of marine diesels from over 25yrs in the business:

1. If you run light load much of the time (as most trawlers do), once a day or so put it under a good load (80 % of max rpm is fine, no need for full power) for at least a few minutes to burn off carbon and oil slobber. You usually get a burst of smoke on power up, once exhaust is clean, so are internal engine bits. If exh is clear in a minute, run at power for at least five.

2. Cooldown prior to shutdown: There are lots of thermal gradients in engine parts when under a load. Pistons, heads, turbos, etc. When running under a heavy load, you want to run engine unloaded for like five minutes before shutdown. Longer for big engines, shorter for little ones. Fortunately for marine diesels, this is handled automatically buy maneuvering to get in a slip or getting anchored up. More of a concern for engines in other applications where a hot shutdown might be more convenient. For us, not a concern. Except maybe gennies, seen many shut down hot, good to give them a few minutes of run to cool down after taking off the load.

3. Warm up/cool down: Don't go to high load until engine is warmed up. Add load gradually when starting from cold. Actually good to add load and remove load gradually even if warm, if practical.

4. Idling: Minimize how much time your engine is at dead idle. There are lots of places on the engine where lubrication is either splash or otherwise marginal. A few more rpm improves things. Mine idles at about 500, once I start it and oil pressure comes up, I run it up to about 800 til ready to go in gear, then back to slow idle. Same with waiting on a bridge, bump up to like 800.

Note: this does not apply to fishing. When fishing I run the engine where I need and it does what it is told. Usually for me that is like 600. Engine is happy when it knows we are fishing so I know it will not harm itself.

5. Shutdown: I usually rev the main engine to like 1200rpm right before shutdown. This is to throw lube oil all over the place internally. Back to idle for like ten sec for turbo to spool down, then off.

None of the above guidelines are that important. I have been around many engines where the duty cycle was brutal, and the engines did fine. But if you can follow them, I think they are somewhat helpful.
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Old 09-16-2020, 10:50 AM   #27
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Thanks for weighing in.
I think many of us have been looking for your insights and experience.

I don't fish with my diesel cruiser but hope mine our equally happy when cruising in new and beautiful places?
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Old 09-16-2020, 11:00 AM   #28
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A full hour at full load is not good or advisable just allowed. People confuse allowed for required and perhaps that occurred here from the Japanese. Do what Ski said, a few minutes at wot occasionally when convenient not every time. You are not running especially slow. IMO they mean idling. personally

I rarely ever ran at WOT except for a brief test from time to time to make sure all was well. IMO 80% or normal high cruise is all that is needed for any carbon removal.

racing the engine in neutral is not required either IMO. A short period of slow running after full load operation is advisable for cool down rather that a sudden shut down but that usually happens while docking.
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Old 09-16-2020, 11:07 AM   #29
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My cruising speed of 7kn is 70-75% of WOT. I don't do much else.
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Old 09-16-2020, 11:08 AM   #30
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I spoke to a Yanmar tech who said to run it at 3000-3500 rpm periodically. We usually do this on a calm day for 20 min or so. I prefer to run it a a lower speed due to the volume in the pilothouse.
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Old 09-16-2020, 07:51 PM   #31
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Quote:
Originally Posted by Nomad Willy View Post
Pmcsurf1,
Can’t read it w big i-pad too.
I assume you’re showing that Yanmar actually said that ... racing the engine.
What I said in post #7 did not include considerations for turbochargers. Sorry.
But what Yanmar said seems applicable to turbos. But I know little about turbos.
It would probably be good advice if one was to read it w/o the racing bit. Why couldn’t they just say something like “advance the throttle quickly to full throttle for two about one second and then back to idle five times” or whatever.

Edit;
I see Frosty wrote;
“ It sounds analogous to that quick "rev" that people of my parents' generation always did to their cars before shutting them off. You know, put it in Park, hit the accelerator and a quick "vrooom!" and then shut it off. Those were gas engines, but was there some basis for it?”

Perhaps people were thinking if an engine was “loaded up” (too much fuel) a blast of throttle would clear it out. Probably not. When the revs hit their high point .. if the ignition was turned off just then the high vacuum in the entire intake tract would suck in lots of raw gasoline. Not good. And while the engine was shut off the fuel on the cylinder walls could wash much of or most of the oil there-on. Not good.

I had totally forgotten about that Frosty.
They did say rev 5 times and then let idle for five mins. Not shut it down immediately.
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Old 09-16-2020, 07:52 PM   #32
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Quote:
Originally Posted by BruceK View Post
Trouble comes from trawlers liking hull speeds and turbos needing to spool up and clean out. My mechanic says run the Cummins hard for 10 minutes before returning to the berth.
I've heard the same.
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Old 09-16-2020, 08:28 PM   #33
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Quote:
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My cruising speed of 7kn is 70-75% of WOT. I don't do much else.
That’s it w FD boats.
You’re running into the brick wall at about .8 knots below hull speed. Going faster is bordering on stupid. Going slower is like slower than the slow. Few skippers can handle that.
Our boat could make a run to SE Alaska .. about 1000 miles. We could probably do it by running 24-7 at night and all. But it would be safer to run at 5.5 knots and burn close to 1/2 gph less. We could easily make the run at 5.5 knots. But I don’t think I could stand running at that speed for 30 hours.

I’m different but in this respect I become quite normal.

So for FD boats you run at about a knot below hull speed ... and that’s it. Small FD boats are a one speed boat .. not technically but for all practical purposes they are.

SD boats are much much more popular. But do burn more fuel.


Pmcsurf1,
Yes not shut down immediately. Trawler diesels should be run near idle for several minutes prior to shut down. I think I said that before (this thread) but wasn’t considering turbos. I did that in all the truck driving I did.
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Old 09-17-2020, 05:35 AM   #34
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The manual for my 315hp 6lpa stp yanmar reads exactly the same. I have concluded that they mean to “blip” the motor to full revs and back 5 times. I do it, in neutral, before entering the marina after putting lines and fenders out. I am pretty sure my neighbours appreciate it and i don't feel such a goose doing it in the marina. I am sure the engineers at Yanmar know a wee bit about their motors. Its a sweet motor but ridiculously large for my little 35 footer. I calculate hull speed at about 7.5 knots.
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Old 09-17-2020, 06:05 AM   #35
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"I am sure the engineers at Yanmar know a wee bit about their motors."

No doubt they can explain everything in their native tongue.

Its the English translation that might be the worry.
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Old 09-17-2020, 06:14 AM   #36
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Think there are competing needs. You want the turbo to cool down as much as possible before the engine stops but remain lubricated during that process. You want carbon to be burnt off before shut down.
The vrooms are brief enough they won’t much effect temperatures during the 5 minute shut down. My understanding is that when operating near WOT under load you burn off carbon deposits. Hence the need to do that if run at low speed, rpm and load for any length of time. I think it doesn’t much matter when you do that as long as it’s done frequently enough to prevent build up of deposits.
I’ve also been taught it’s good practice to vary your rpms a bit. Of course this is most important to a new engine but also not a bad idea with one with hours on it. Most boats have sweet spots. You know how many rpms to get to 1.1 s/l or hull speed. You know how many to get on plane. So you tend to run at several fixed rpms. Never really understood this as continuous duty engines in various applications (marine and otherwise) are run at fixed rpms their whole service lives without detriment.
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Old 09-17-2020, 08:11 PM   #37
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Quote:
Originally Posted by FF View Post
"I am sure the engineers at Yanmar know a wee bit about their motors."

No doubt they can explain everything in their native tongue.

Its the English translation that might be the worry.
Lost in translation. Lol
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Old 09-17-2020, 08:12 PM   #38
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Old 09-17-2020, 09:55 PM   #39
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Me-thinks that's the important bit.

I don't think they are talking about when you are running your boat normally...they are talking about when you are operating at a very slow speed, like trolling for salmon, or if you are charging your batteries at anchor at (or near) idle.
That's the key here, running at slow speeds all the time or for very long periods (over several hours at a time according to the mechanic I have trusted for years) is NOT what a turbo was designed to do. Running the engine up under load to 80% load for 20 minutes or so every few hours to burn off deposits as a routine way to run these engines seems like whistling past the graveyard in an effort to fool the engine that it was run "normally" all day, but apparently is accepted as one antidote to non-boosted running. I know some run these Yanmars (my own is a 315 HP turbo'd 6LPA-STP, 3800 RPM WOT) lightly loaded all the time and say all is well, but where are these owners a number of owner turnovers later when the engines need turbos replaced prematurely? For those running out at speed to fishing grounds and low then RPMs for all day with running up to around 80% load for 20 minutes or so every few hours and lastly running at a good load all the way home, none of this idle revving should be necessary. I think Mainship elected to include turbo'd Yanmar engines in their "trawler" designs was so that their marketeers could advertise the concept of being able to run the boats at "high cruise," but the reality of the high fuel usage hits the pocketbook of people who actually prefer to go slowly too hard or their operating areas just preclude speedy (wakey) operation. In a vessel designed as a recreational trawler, they just seem to be the wrong type engines for which all these accommodations must be made.
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Old 09-21-2020, 12:57 PM   #40
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There are two different issues here:

Carbon accumulation - this comes from running the engine too cool. At what RPM does your engine gauge reach 170F+ ? Try to always run above that speed and you'll have very little carbon problem. The people who get in trouble spend lots of time at 1400 rpm or below. I've got 2300 hours on my Yanmar 4JH4. 90% is at 2100rpm (3100 max so 67%). I do go to full throttle about once a week for 5 minutes to make sure it still doesn't smoke and that it doesn't start to overheat (which would indicate problems in the cooling system or exhaust elbow.

If you have two engines and you can maintain a straight course, you can do this one engine at a time while reducing the rpm in the other engine. This reduces fuel burn and noise.

Turbocharger - if you have a turbo before shutdown it's a good idea to blow any accumulated crap out. I was taught at a Yanmar Boat Owners diesel seminar to advance the throttle three times to the stops in neutral (Vroom, Vroom, Vroom). Then idle a minute and shutdown.
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