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Old 09-02-2014, 06:33 AM   #41
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The 3208 natural cranked out around 220hp, last almost forever

However climbing a hill those 220Cat Hp were more like 150 Detroit HP. , but it would go a long time before being thrown out.

Cat has a great sense of humor in their HP ratings
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Old 09-02-2014, 07:14 AM   #42
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Look at the old Detroit 53, 71, 92 series life span when Johnson Towers got through with em. Pumped them up to where a non turboed engine would have a 20-30 thousand hour life span theirs 1200 hours then ready for MOH. Cat 3208, pass 350hp or so and they blew themselves up in no time. The 3208 natural cranked out around 220hp, last almost forever. As with all things in life, a compromise.
Well then they weren't continuous duty engines after those mods. And you are discussing old technology engines. That's the larger point here which almost everyone seems to be missing, or simply failing to understand. The continuous duty engine, turbo'd or not of the same block is a different sub-model of that base engine. A good example is the ACERT Cat engines Bill provided a link to.

By the way the 650 hp 8v92Ti's in my boat at 3000 hours surveyed out beautifully.

The apocryphal evilness of turbochargers has become yet another dockside version of an urban legend, based on ancient lore.
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Old 09-02-2014, 10:20 AM   #43
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Old two strokes did over fuel and carbon up if not run with moderate load from time to time. Newer four strokes do a better job of fuel metering even at low rpm. All engine s benefit from low loading that's why lehmans are still running.

The simple is better argument does have some validity IMO with V8 a because they may have 2 of everything.
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Old 09-02-2014, 10:23 AM   #44
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For some reason old diesel stories carry forward while old model T stories are not assumed to apply to today's Cars.
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Old 09-02-2014, 10:24 AM   #45
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Per JD,



Which would be better for a FD boat that requires 85 HP to run hull speed in calm water/winds?
  1. An M1 enigne running 105 HP?
  2. An M2 engine running 121 HP?
  3. An M3 engine running 135 HP.

Loading is a very important limitation...

Later,
Dan
Pretty much irrelevant which you choose. With a FD boat you will spend virtually all of your time using 30 or 40 hp. At those power settings, rating is completely unimportant. For example, my CAT 3306 comes in 5 ratings - A for continuous to E for 250 - 1000 hours per year. At prop demand, the A rating will produce 91 hp at 1500 rpm while the E rated engine will produce 90 hp at 1400 rpm. My 270 hp C rated engine produces 85 hp at 1500 rpm, which is enough to move a 65 ton boat along at 8.5 knots. To move her at hull speed, I need 175 hp, which I use for about 15 minutes every 24 hours or so to heat up the EGT to 875 degrees or so from its normal 475 degrees.

The point is, that when you are talking about FD boats, you need a fair amount of horsepower to run at hull speed without going over 80% or so of max power, but a small fraction of that to run at normal cruising speeds. Since you run at low power settings 98% of the time, the rating of the engine has no impact on longevity, at least IMO.
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Old 09-02-2014, 10:48 AM   #46
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I am gathering "over" turboed engines are not necessarily evil, but their owners can be by running the hell out of by over stressing them.
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Old 09-02-2014, 10:56 AM   #47
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For some reason old diesel stories carry forward while old model T stories are not assumed to apply to today's Cars.
I remain impressed by what the MV Detroit did 102 years ago. Here we have a 38 foot boat with a 2 cylinder gas engine that not only crossed the Atlantic but went on to St Petersburg too. The trip was 6500 miles taking less than 1000 clock hours.

The logs go into great detail as to how they read the weather to avoid storms and big seas. During the previous 200 years much knowldege was gained on Atlantic weather systems by the commercial and passenger sail boats. Weather forecasting was both an art and science based upon surprisingly good weather models and measurements of the time facilitated by telegraphed actual reportings.

As shown by Leif Ericsson, staying North for Detroit was a weather wise decision. For the large and small MVs of a century ago, fuel and coal stops could occur in Labrador, Greenland, Iceland and Scotland.

But none of this makes me hanker for a 100 year old gasoline engine in my boat. Scripps made boat gas engines up until the late 40s when the 6-71 and other two strokes took over the pleasure boat market quickly followed by a plethora of 4 strokes.
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Old 09-02-2014, 11:07 AM   #48
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I am gathering "over" turboed engines are not necessarily evil, but their owners can be by running the hell out of by over stressing them.
Anybody here intentionally overstressing their engines whether turbo or NA? Please raise your hand if so.

Anybody here trying to figure out how to ignore routine maintenance schedules by hour and time as posted by the diesel engine builder? Based upon recent threads it appears many on TF do.

So where lies the greatest danger to our beloved marine diesels no matter what make or model?
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Old 09-02-2014, 12:14 PM   #49
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Tony Athens at Seaboard Marine wrote an article back in 2008 entitled "Continuous Duty - A Different Perspective" which I believe presents an honest and knowledgeable discussion of the subject, and is worth a read by anyone interested in this thread. It may change the way some view the term 'Continuous' as it relates to the way we operate and evaluate our diesels.

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Old 09-02-2014, 12:31 PM   #50
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We here are not, as a general rule, sport fisher go fasters with that mentality. Have an over turboed boat and run it hard then bye bye. The trawler forums members are the choir so they are not the ones that one needs to look to to raise their hand. Go faster ones need the sermon.
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Old 09-02-2014, 04:44 PM   #51
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Really! With 99%+ of diesel engines sold today having turbos the jury voted decades ago. My experience includes up to 4000 HP commercial diesels working at full WOT throttle load over 50% of the time and with quad turbos and JWAC.

A look at the automotive diesel market shows the same, few if any diesel NAs are sold today in the automotive or light truck market.

And we are speaking of tens of millions of these turbo diesels in use today with the turbo diesel market growing dramatically to permit mandated fuel economy standard to be achieved.
Then I misunderstood the question.

I thought we were talking about engine design not markets.
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Old 09-02-2014, 05:07 PM   #52
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Then I misunderstood the question.

I thought we were talking about engine design not markets.
You are right, the markets have spoken. And for decades the markets have demanded reliable, cost effective, emissions compliant, fuel efficient and ever smaller Diesel engines.

There is no market for a Diesel engine embracing designs outdated decades ago, except as replacement engines where issues like fuel burn rates, weight, size and emissions don't matter. This includes far more iron than a FL so don't take it personally.
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Old 09-03-2014, 07:00 AM   #53
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>The point is, that when you are talking about FD boats, you need a fair amount of horsepower to run at hull speed without going over 80% or so of max power, but a small fraction of that to run at normal cruising speeds. Since you run at low power settings 98% of the time, the rating of the engine has no impact on longevity, at least IMO.<

As almost no one wants to pay double for that last K the solution is to prop the vessel so it is operating at 80% of cont rated power at the CRUISE RPM you have selected.

Then the ability of the higher short term loadings can allow hull speed or super wake making of semi displacement on a short term basis , 30 min to 12 hours , depending.
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Old 09-03-2014, 10:08 AM   #54
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The only purpose of a turbo is to make more power from less swept area than is otherwise possible. The size of the turbo depends on how much fuel at what rpm and load and the amount of air needed to meet that. A small engine with a "big" turbo can make comparable power to a larger non turbo engine. The smaller engine has less swept area (cubic inches) therefor less parasitic losses to produce its power. ie, more efficient. However, if your turbod engine is rated substantially higher than you need or can use efficiency is reduced. It needs fuel, air and load to get to its "sweet spot" A Cummins 6BTA at 370 hp is a very inefficient engine at 1200 rpm due to a lack of turbo boost, you may as well be running the 120 hp non turbo version, and if that is the normal usage you would be much happier with it. Newer electronic engines are better at low speed fuel control but still cannot vary the turbo to produce boost at the low loads we are discussing. Therefor, if you want maximum fuel economy you still need to size the engine to the load. If you need 85 hp to go 8 knots then get an 85 hp rated turbod engine. At 8 knots it will be fully loaded and as efficient as possible. If reliabilty is a concern, or longevity, get a bit larger (not the same ci with more turbo and fuel) engine. More swept area equates into less stress, but also less efficiency.
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Old 09-03-2014, 10:35 AM   #55
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The only purpose of a turbo is to make more power from less swept area than is otherwise possible. .
Not to mention to meet today's marine emission's requirements.
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Old 09-03-2014, 10:37 AM   #56
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These discussions make it sound as if people are swapping engines. In reality most keep the original engines. All the theory doesn't matter unless choosing engines for a new boat or repowering.
The vast majority of users won't notice the fuel economy difference if their boat has low or high power engines at 6 knots.
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Old 09-03-2014, 11:14 AM   #57
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Continuous rated engines generally means it can be run at full power 24/7/365. Usually something like 25hp/liter or so. Higher rated engines can be run at 24/7/365, but not at full power. The high rated engine might be capable of making 60hp/liter, but can't do that continuously. Run it at 25hp/liter, either engine, and they both can go forever.
Excellent explanation!

For example our Cummins 330's are rated at "recreational duty", but that rating is for "normal cruise RPM". Run the same engine at hull speed and there is no issue.
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Old 09-03-2014, 01:35 PM   #58
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A Cummins 6BTA at 370 hp is a very inefficient engine at 1200 rpm due to a lack of turbo boost, you may as well be running the 120 hp non turbo version, and if that is the normal usage you would be much happier with it.
Actually, the 370B is not that bad down low. On the 2.7exp prop curve:
At 1200rpm, 31.2hp, 1.9gph, 16.4hp/gph.
At 1600, 67.8hp, 3.7gph, 18.3hp/gph.

Not stellar, but not far below the gold standard of 20hp/gph.

Edit: More data. Don't feel like working.

For the Cummins 220B, which is same disp as 370, but with mild turbo and no aftercooler.

At 1200rpm, 27hp, 2.0gph, 13.6hp/gph
At 1600rpm, 59.3hp, 3.5gph, 16.9hp/gph.

So at trawler loading, the hyped up 370B seems to be more efficient than the 220B!! Fairly surprised by that. Data from Cummins published performance curves and tables and prop curve calcs.
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Old 09-03-2014, 03:14 PM   #59
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Actuall use does not bear those figures out. At 1200 rpm after several hours the 370 6BTA is a nasty beast. You cant sit in the cockpit and fish. Every few hours we pulled up the lines and ran it up to speed until they cleaned up. Then good for a few more hours. High hp DDs are the same, just not meant for low speed operation.
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Old 09-03-2014, 03:55 PM   #60
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That is very surprising and counter to any other b series experience I have heard of. I wonder if something is wrong with them.
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