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Old 03-17-2016, 05:05 PM   #21
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Hello Jansuz and congratulations on the new boat. Hopefully this will help. My boat has 3208 Turbo Caterpillars, max loaded RPM is 2800 so 75% of load is 2100 RPM.

I run my engines at 1200 - 1300 RPMs or 45% of max load which gives me about .5 kt below hull speed. Every four hours I bring the engines up to 2100 RPMs for 5-10 minutes just to clear out the turbo and ensure everything comes up to proper temperature, then back down to hull speed.

If you are not already a member take a look at boatdiesel.com, it's $25 to join and there is a wealth of information to be had.
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Old 03-17-2016, 05:38 PM   #22
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My old sportfish had Cat 3208 Ts rated 320 hp.

I used to troll for fish hour after hour at idle to 1000rpm in gear and sometimes one engine at 1000 or less.

Followed the dock telegraph advice of 10 minutes at high rpm (200 or so under max) every 4-6 hours of trolling. The engines would belch smoke for about 2-3 minutes, clean up and be smokeless for the rest of the time.

I sold the boat (1986 boat/engines) 11 years ago with around 3700 hrs on the engines and last year the new owner called, said he had to get new props...changed then a tad in size and pitch...and the boat has never run better picking up several knots throughout the rpm range.

My guess is the engines now have 5000+ hrs on them based on that the new owner uses the boat a lot.

My point was that those turbo engines spent a lot of time fishing at idle or very low rpms with the recommended "blow out"...and seem to be surviving just fine. Just remember, these were 1986 engines (technology).
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Old 03-17-2016, 05:53 PM   #23
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It was repowered in 2011 with Sabre Perkins M225 TI and there is 364 hrs on it. The oil was changed once (how it should be) and sample was analyzed - all OK.
Consider this only a question and the fact that the oil analysis was good indicates that things are fine but....

Even though it only has 364 hours on the engine, I would think that good practice would be for the oil to have been changed yearly. Oil, once it has been run, "deteriorates" just sitting in the engine.

Now, oil analysis seems to contradict that in this case. Is the concept of at least yearly oil changes something that I need to just get over?
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Old 03-17-2016, 06:12 PM   #24
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Consider this only a question and the fact that the oil analysis was good indicates that things are fine but....

Even though it only has 364 hours on the engine, I would think that good practice would be for the oil to have been changed yearly. Oil, once it has been run, "deteriorates" just sitting in the engine.

Now, oil analysis seems to contradict that in this case. Is the concept of at least yearly oil changes something that I need to just get over?
Reread the thread...I think the oil analysis was done after the the last oil change...when that was?
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Old 03-17-2016, 07:58 PM   #25
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Janusz,
Find out from the manufacturer what the engine will burn in gph at rated rpm and wot. Get your own boat propped to rated rpm at wot. Then do the best you can at determining how many gph your boat burns at any given rpm. If your cruise burn is 4gph and at wot it's 8gph you are at 50% load at cruise rpm. And if your engine makes 200hp at rated rpm then w the above example you're making 100hp at cruise.

I think the above is correct. Please set me straight if not.
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Old 03-17-2016, 08:01 PM   #26
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I believe that is a Marine Trader, right?
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Old 03-17-2016, 08:02 PM   #27
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Originally Posted by dkasprzak View Post
Hello Jansuz and congratulations on the new boat. Hopefully this will help. My boat has 3208 Turbo Caterpillars, max loaded RPM is 2800 so 75% of load is 2100 RPM.

I run my engines at 1200 - 1300 RPMs or 45% of max load which gives me about .5 kt below hull speed. Every four hours I bring the engines up to 2100 RPMs for 5-10 minutes just to clear out the turbo and ensure everything comes up to proper temperature, then back down to hull speed.
Load is not determined by percentage of engine RPM. On mechanical engines it is percentage of maximum fuel rate. On electronic engines it is position as a percentage of maximum fuel limit.

Many engines today have guages to measure load. However, in it's most basic form it is the horsepower used as approximated by the fuel used.

Now, it's more complex than I'm presenting here, but here is a simplified example. I have engines which at WOT use 117 gph of fuel. I'm targeting 75% load so I'm targeting 88 gph of fuel required. These are 1200 hp engines so that is my best estimate of using 900 hp. 117 gph of fuel is at 2025 RPM (which is 84% of max RPM of 2400).

I can site a small Riva for which cruising speed is rated by the manufacturer at what ends up being 87% of max RPM but only 77% of maximum fuel usage.
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Old 03-17-2016, 08:15 PM   #28
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Reread the thread...I think the oil analysis was done after the the last oil change...when that was?
Ah yes. Thanks. I misread that.
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Old 03-17-2016, 09:28 PM   #29
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Is that engine a non-electronically controlled model?
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Old 03-17-2016, 11:44 PM   #30
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The engine is not electronically controlled. No computers.

The boat is Ocean Alexander -OA - not Marine Trader.

The oil analysis was done by my surveyor-mechanic 2 days ago using a Surrey lab. The oil change was approx. 1,5 yrs ago by previous owner.

He kept all the receipts, manuals, bills, ship's log etc and the whole documentation which takes a whole shelf and weighs at least 20 lbs, I am sure. That was one of the compelling reasons I bought this boat.
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Old 03-18-2016, 12:43 AM   #31
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Steve D'Antonio is a member of Trawler Forum and contributes on occasion. Perhaps he will add to this discussion...
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Old 03-18-2016, 01:36 AM   #32
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Steve D'Antonio is a member of Trawler Forum and contributes on occasion. Perhaps he will add to this discussion...
What do you feel is missing? Seems like some good thoughts are springing forth. The one hope I have is that the new owner will read the manuals and prop curves for this specific engine.
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Old 03-18-2016, 02:13 AM   #33
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Old 03-18-2016, 10:27 AM   #34
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Below is a timely (yesterday) quote from Steve D'Antonio copied from another forum on this very subject:


"Thu Mar 17, 2016 5:17 am (PDT) . Posted by:
stevedmarine

High revs, 75% load is often more than adequate to achieve the desired ideal temps within the engine, makes good sense for several reasons in addition to soot reduction. Most trawler engines are woefully and chronically under-loaded, which leads to excess soot formation in combustion chambers and in turbos and exhaust systems, as well as wet stacking in some cases. Light loading also leads to overly cool combustion chambers/exhaust gas temperature and "cold" oil. The former, again supports build ups on valves and rings, and the latter leads to sludge and then varnish formation. Thus, a hard, 75% or more load for 10 minutes out of every four hours will serve to stem some of the effect of light loading.

Having said all that, it's best not to do this immediately before shut down. This sort of loading does get things hot, which is good under most circumstances, but not immediately before shut down. Oil that remains on very hot surfaces like turbo shafts and exhaust valve stems after shut sown will undergo a process known as coking or carmelization, the oil essentially bakes onto these surfaces, which can impede oil flow and lubrication in the future.

If you carry out a hard run, be sure to follow it 10 or more minutes of light or no load to allow these regions within the engine to cool off. Often, but not always, that's accounted for by docking time alone.

Steve D'Antonio"
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Old 03-18-2016, 11:06 AM   #35
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Thanks DD,
Don't see much if any softening.
What I like about his post is that he actually tells what will happen inside the engine and why. May of us here on TF have been saying it's not good to run light load but not known the specifics of why not. I first heard SteveD advise a 75% load about the time I started on TF .. 07. Edit: ... I just remembered his specifics at that time. It was "75% load 75% of the time". Of course at that time I like many others thought it was 75% of rpm. Soon found out that was way different. Because of the big bend in the power curve one can be at 50% rpm and the actual engine load could be as low as 20% ... or even less depending on many variables. Then it's so hard to get good burn numbers and most everybody thinks low burn numbers are "to die for" as the girls say and other trawler skippers will be envious and respectful of your numbers if they are low it's hard to resist. Then when you see someone posting numbers lower than yours ya better out do him.

So I'm glad to see SteveD post some specifics that should open some eyes and minds. I thought I was at 75% load until I ran some numbers and found I actually was at 50%. Soon w my little laser thermometer I'll get some more numbers to add to what I know and subtract from what I thought I know.
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Old 03-18-2016, 11:59 AM   #36
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Here is another perspective from Tony Athens of Seaboard Marine


"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.."


and


"...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..
In closing, I’ll mention that although this topic is brought up quite often and many people preach that you’ve got to use a diesel hard if you want it to last, I’m still waiting to find one that was rebuilt before its time due to low speed use..Just the opposite seems to be always the norm."


For the modern diesels, I'm not sure that the idea of 75% load 75% of the time still holds true.
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Old 03-18-2016, 12:09 PM   #37
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Quote:
Originally Posted by dhays
For the modern diesels, I'm not sure that the idea of 75% load 75% of the time still holds true.
And...what defines "modern diesel?"

My next post lays out my own confusion with all this.
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Old 03-18-2016, 12:12 PM   #38
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Thanks Diesel Duck for that D'Antonio piece.
It helps.

I've mentioned before that I am moving from gas to diesel.

While it is coming, the curve is still fairly steep, for more than a couple of reasons; having had gassers that hit 6000 RPM WOT, it's hard to talk in terms of 1400-2000; 80% of WOT RPM was always the "don't go over" mark and more than anything else, this old brain is slower and less absorbent..

Load is the tough one and I have found almost all brokers and owners I have spoken to recently are uneducated on this as well. Most of them talk about RPM, not load, not fuel burn and few have a real grasp of over/under propping. I'm having a hard time making sense of the two terms (load, fuel burn) both in general and when trying to equate them to a specific boat on the market.
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Old 03-18-2016, 12:26 PM   #39
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So I'm glad to see SteveD post some specifics that should open some eyes and minds. I thought I was at 75% load until I ran some numbers and found I actually was at 50%. Soon w my little laser thermometer I'll get some more numbers to add to what I know and subtract from what I thought I know.
Many people look at RPM and think they're running at a higher load than they really are. In your case it was an extreme difference between your actual and your perceived.
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Old 03-18-2016, 12:50 PM   #40
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Janusz - FYI, I have two engines identical to yours and know them and their issues well. How the exhaust system is set up in your newer install whether angle on turbo exhaust/shower run or as compared to the WL is very important.

To complicate the load question even more - a 6bt Cummins can have a dependable HP rated range from about 210 to 370. Running the 210 version at 75% is like running the 380 at 40%. Same holds true for many other brands.

I would and do follow Tony's, Cat and Perkins Sabre (owned by Cat) guidance. It could be argued that Steve's comments are not always new century relevant as they disagree with some current engine builder's positions on load. Steve is correct, keep the EGTs and oil temps within spec, which is easily doable on many current ( this century) engines without running the "load" up.

Many Nordhavn and other blue water owners cruise their vessels for days on end at loads well below 75%, current engines again mind you.
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