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Old 08-31-2014, 08:01 PM   #1
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Continuous Rated Engines

This comes adrift from the Showtime and Minimum RPM threads.
I`ve heard some engines are rated for continuous use, like JD and Gardiner. What exactly does that mean? Who assigns the rating? Of the maker, common experience,and a rating agency, the first is most likely. How reliable is that? Any maker could claim it as part of a sales spiel, but it could all come undone in practice.
Which engines have such a rating, and why? The Dauntless experience suggests at least one FL deserves the rating. One member was astounded I didn`t already rate the FL, I didn`t, I own 2 of them, I`m still not sure. So, would we include the common FL 120 and/ 135? I`ve not heard Ford or Lehman did. Who apart from Richard has run one for days on end?
And let`s not get too fixated on the FL, there are plenty of other possibilities in engines out there.
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Old 08-31-2014, 08:11 PM   #2
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ISO 3046 has the answers.
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Old 08-31-2014, 08:13 PM   #3
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Our Lugger L1066T is rated for continuous duty at 2200 RPM @ 135Hp, which is exactly what we run all the time.
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Old 08-31-2014, 08:16 PM   #4
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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.
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Old 08-31-2014, 08:18 PM   #5
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Old 08-31-2014, 08:20 PM   #6
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... Run it at 25hp/liter, either engine, and they both can go forever.
Interesting. The FL 120 is 6.2L.
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Old 08-31-2014, 08:50 PM   #7
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The 25hp/l I guess better applies to turbo engines, a nat asp engine is going to be hard pressed to get there at all. Go with the mfr's specs for rating class, some turbo engines are 30+ hp/l at continuous, nats will be much lower.
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Old 08-31-2014, 09:36 PM   #8
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My naturally-aspirated JD4045 (80 horsepower) at "high cruise" (hull speed) of 2200 RPM is at 75% load (3 versus 4 max. gph at 2400 RPM). "Normal cruise" (one knot below hull speed) at 1800 RPM is at 43% load (1.7 gph).
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Old 08-31-2014, 09:46 PM   #9
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Quote:
Originally Posted by BruceK View Post
This comes adrift from the Showtime and Minimum RPM threads.
I`ve heard some engines are rated for continuous use, like JD and Gardiner. What exactly does that mean? Who assigns the rating? Of the maker, common experience,and a rating agency, the first is most likely. How reliable is that? Any maker could claim it as part of a sales spiel, but it could all come undone in practice.
Which engines have such a rating, and why? The Dauntless experience suggests at least one FL deserves the rating. One member was astounded I didn`t already rate the FL, I didn`t, I own 2 of them, I`m still not sure. So, would we include the common FL 120 and/ 135? I`ve not heard Ford or Lehman did. Who apart from Richard has run one for days on end?
And let`s not get too fixated on the FL, there are plenty of other possibilities in engines out there.
Most any diesel can run continuously, just not at peak output. The ratings relate to the percentage of time the engine can run at peak power. My CAT is a 'C' rated 2200 rpm motor at 270 hp that can run 24 x7 for the rest of my life at 1500 rpm and is expected to run 1,000 - 2,000 hours per year. The 'A' rated is continuous at 2000 rpm and 215 hp with an annual hour time of 5000 to 8000 hours, and the 'B' at 2000 and 235 hp and 3,000 to 5,000 hours.

So it really boils down to how you use the engine that determines what rating is most appropriate, with higher rating accomplished by tuning down the max rpm and hp. In trawlers, since they rarely run at full power and only run 1,000 hours per year or so, the rating probably doesn't matter much. Although I am happy to be corrected on this impression....
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Old 08-31-2014, 09:53 PM   #10
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Rating should be by the manufacturer. For older engines I have often seen it expressed simply as 'for continuous operation do not exceed 85% of max rpm'.

I have a pair of John Deere 6068's, with their M3 rating. This rating specifies full power operation must be limited to 4 hours out of every 12. On the other hand, their M1 rating for the same engine allows 24 hour full power operation ie continuous. The different ratings are achieved by the dealer changing the ECU via a laptop. Just how many things change I have no idea, but here is a couple: WOT comes down from 2600 to 2400. Power output drops from 201HP to 158HP. The maximum power and torque curves change shape a bit, and with M3 rating I still have the full 201HP available at 2400rpm. The engine has an electronic governor but is Tier 2 and not fully electronic - the injectors are not fully electronically controlled like the later common rail Tier 3 engines are.

For my M3's, load factors must also be below 50%. Load factor is defined as fuel burned over a period of time divided by full power fuel consumption over the same period. The other 8 hours out of 12 must be at cruising speeds. Cruising speeds are defined as 200 rpm below WOT, or 2400 rpm for my M3's.

In practice, due to hull shape and weight, gear ratio and prop size I find my sweet spot is in the 60 to 75% of WOT area. So, 1500 rpm for 7.9 kn at 15 lph total up to 1950 rpm for 9.5 kn at 30 lph total. There has to be a good reason to want the extra 1.6 kn at double the fuel consumption! And for me to run at 10 kn or more uses a lot more fuel for little real benefit, as I'm still in displacement mode for my SD hull shape. If I wanted to plane I would need at least 50% more installed HP and probably more like double. It gets hard to do that at reasonable fuel consumption once you are over 40 ft with all the space and comforts of home and associated weight on board.

It seems that many Lehman owners also tend to operate in the 60-75% of WOT area and expect and report long service life. I suspect that if you ran a high rpm car diesel engine like that, ie 60-70% would you also get long reliable life. If so then car diesels would seem to be a pretty good option for a planing boat. Just choose the right size so you can keep the loading down.
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Old 08-31-2014, 10:39 PM   #11
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For most practical purposes with a modern common rail fully electronic motor you can pretty much dial in the ratting equivalent use with the throttle. Or you can have a tech from the company come down and hook your motor to a computer or exchange a chip and set up a new ratting. What happens is that the electronics tell the motor how much fuel it can burn and how much HP can be pulled out at what RPM. So a 6+ Li engine can be M1 (continuous rating) at say 180Hp at 2200rpm or bumped up to 300+ Hp at 2600rpm at M4 pleasure use say 4/12 hr max rpm cycle. If you run the M4 at 1800-2200 rpm you can use it like an M1 24/24 You are just pulling less power out of the unit and stressing it less so continuous use will not harm it. A good genrator motor should be set up like an M1 particularly if used for long periods. A ocean crossing vessel would also benefit from M1 ratting or reduced throttle due to long continuous running hours.
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Old 08-31-2014, 11:27 PM   #12
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Quote:
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Our Lugger L1066T is rated for continuous duty at 2200 RPM @ 135Hp, which is exactly what we run all the time.
If so, this would equate to a fuel burn of about 7 gph if you're pulling 135 hp. Most N47s seem to have a normal rate closer to 5 gph for coastal and 4 gph for blue water cruising. What is your fuel burn and RPM at coastal and economy cruise?
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Old 09-01-2014, 12:34 AM   #13
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If so, this would equate to a fuel burn of about 7 gph if you're pulling 135 hp. Most N47s seem to have a normal rate closer to 5 gph for coastal and 4 gph for blue water cruising. What is your fuel burn and RPM at coastal and economy cruise?

From what we've seen we burn 6GPH with genny, we don't have any fuel flow monitors yet. But that's just what we've seen when we compare our log book to fuel levels.
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Old 09-01-2014, 05:58 AM   #14
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, Who apart from Richard has run one for days on end?
Once an engine is up and running it's in it's happy place. It's starting and stopping, heating up and cooling down that's hard on an engine or motor.

Here's is some info on CAT engine ratings.

http://tinyurl.com/pdzm4uq

http://tinyurl.com/ohcbhg9
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Old 09-01-2014, 08:30 AM   #15
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Where does torque fit into this, I may have been living under an illusion that as hp was dialed down then torque increased, kindda a whack a mole or ohms law with voltage and amps.??
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Old 09-01-2014, 09:12 AM   #16
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Boatdiesel.com has a wealth of information and comment on this and similar issues.

A true continuous duty engine is a de-rated version on the same block as say, a higher horsepower but intermittent use version. Thus you will see the same engine with different version putting out different HP at the same RPM.
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Old 09-01-2014, 09:20 AM   #17
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Mule; Here is a full explanation of the mathematical relationship between torque and HP
HP = Torque x RPM 5252

Power and Torque: Understanding the Relationship Between the Two, by EPI Inc.
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Old 09-01-2014, 10:02 AM   #18
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I agree with most of the comments so far and 25 hp per liter is a good rule of thumb for 24/7/365 use of turbocharged engines.

But let me digress a little bit and talk about ratings in general. The manufacturer assigns the rating. For some, Yanmar in particular this is a marketing/financial ploy and has little basis in engineering, testing or experience.

For Yanmar recreational engines the ratings go something like this: full power for 2 out of 8 hours and 200 rpm off of top forever. And the warranty that backs that statement up is two years at 200 hours per year. See the disingenuity in those statements -.

Running a 70 hp per liter engine at 200 rpm off of top is something like 55 hp per liter. So Yanmar warrants an engine to run continuously at double what the JDs of the world say for at least 400 hours over two years.

Why? Easy, they don't expect to have a warranty claim in that period.

Yanmar is by far the worst in the use of this gimmick. JD one of the best.

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Old 09-01-2014, 11:05 AM   #19
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The most honest engine raters are those that use their engines for commercial gensets, notably Cat and Cummins which are the most popular in the 100 to 200 HP range - operating at 1800 RPM.

The Cummins 6BT genset gives 24/7/365 numbers at 112 KW or 150 HP and Cat's C6 is rated at 138 KW or 185 HP. These two are 5.9 liter engines. One of the most popular gensets is the 7.2 liter Cat C7 rated at 150KW or 200 HP. All three can be purchased with a cradle to grave warranty if you adhere to the maintenance programs.

The Cummins 6B block in its marine propusion variant can be goosed up to 400 + HP and the C7s 450 HP so the genset versions are pretty well loafing. Alas the underachiving C6 has the same marine HP as genset HP for continuous duty at 1800 RPM. The Cat C6 (or Perkins Sabre 225 TA when rebadged and painted blue) sits in my vessel as the propulsion engines.
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Old 09-01-2014, 02:14 PM   #20
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Mule; Here is a full explanation of the mathematical relationship between torque and HP
HP = Torque x RPM 5252

Power and Torque: Understanding the Relationship Between the Two, by EPI Inc.
THis formula is a total over simplification and in fact only works on their little 12" crank example.

the relationship between torque and HP are dependent upon the engine design itself.
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