Propping for WOT and 80% cruise

DM sent.

I have looked into this quite a bit over the years. I had CAT 3208s for 16 years and now C18s. There is the common folklore about running modern diesels at 80% load for long distance cruising. This is not what CAT recommends in their literature. Most of our CAT boat diesels are E rated engines. The following is the typical wording used throughout the CAT operations manuals and literature:

E Rated Pleasure Duty
• For infrequent use in variable load applications where full power is limited to one hour out of every eight hours of operation.
• Load Factor: Up to 30%
• Typical Annual Operation Hours: 250 to 1000 hours
• Typical Hull Forms: Planing
• Typical Applications: Pleasure craft, harbor patrol boats, harbor master boats, some fishing or patrol boats, sportfishers, motoryachts, and cruisers.

That means limited WOT running at rated load and rated speed up to 8% of the time (up to 30% load factor). But this load factor is your average load factor to achieve the CAT service schedule which is 10,000 hours for a major on C18s.

From the CAT literature on industrial engines that are actually a bit derated from our marine engines:


The load factor is limited to 35% for the average over all use not just WOT full load use. And next again from the CAT documentation is an example duty cycle for a D rated intermittent duty engine. This engine has a 50% duty cycle rating with a typical duty cycle shown:

This seems to me to be clear guidance from CAT on where the average engine load needs to be for long distance cruising. Also my CAT C18 manuals clearly provide guidance on my cruise RPMs and say I shuold cruise at 1900 to 1950 which on my 68 ft Viking Princess is a 65-70 percent load.

I believe that technically the Cat 3406E-800 evolved to the C-15. That would be its equivalent.

What I posted above is not CAT C18 specific. It is the load and duty rating guidance across many of the large CAT industrial diesels including the C15, C18 and C32.

What you posted has nothing to do with load at cruise or continuous load and CAT does indeed recommend 80% load as an all day, every day, cruise speed for the C18 and most all other E rated CAT marine diesels. What you posted states that you can run an E series Marine C18 at 2300rpms/100% load for 8% of the time during it's life, or for 1 hour every 8 hours.

Cummins is easier to find than CAT (will try to find CAT's later, nowhere have I seen CAT recommend rpm's for cruise on their modern diesels)
:
High Output (HO)
This power rating is intended for infrequent use in variable load applications with a load factor of 10-30 percent. Full power is limited to one out of every eight hours of operation. Reduced power operation must be at or below 80 percent load.

Engines with this rating are intended for powering recreational use vessels only. Use of High Output ratings in commercial applications will at Cummins' discretion void the warranty. Commercial use is defined as any work or employment-related used of the product, or any use of the product which generates income, for any part of the warranty period, even if the product is only occasionally used for such purposes.
Marine Ratings and Definitions | Cummins Inc.

What I posted has everything to do with load at cruise or continuous load. What I posted is also directly copied out of CAT literature and not from random mechanics or dock folklore. The images I posted directly show that when CT says 30 percent load factor, that means the average load factor should not exceed 30%. Other than the 8% of 100% WOT operation, you cannot just go to 80% and run forever. That gives an average load factor of way higher than 30%.

The following show how to calculate load cycle and ratings. Again directly out of CAT literature. Your Cummins example seems to say exactly what I am saying as well. Yes HO can do 1 out of 8 hours but the average load factor should be 10-30%. In my post above, look closely at the duty cycle figures, these show the WOT but also what is needed on average when not at WOT.

Let me try to make this a little simpler. CATs D rated engines say the following. Look closely at the figure which shows what needs to go with 10% WOT for a D rated engine. If your 80% all day to be correct, would require a B rated heavy duty engine.
From CATs literature for D rated engine:
Load factor limited to 50%.
Time at full load not to exceed 10% of the duty cycle or 30 minutes max, followed by one hour at Intermittent.
(see Figure 3 for typical IND-D Rating Duty Cycle)

You are comparing apples to oranges. IF you look in your CAT manual it will state that you can cruise your E rated Caterpillars at 80% load all of the time. An email to Caterpillar USA will tell you the same thing. I don't know where you are pulling your information from, but I have done several hundred NEW CAT engine start ups on all E rated diesels with many different CAT dealers and have done some seatrials with Corporate CAT as well and they all state 80% load as CONTINUOUS (cruise) speed. I don't have any CAT manuals handy, but 80% load or less continuous is what the E series are rated at, and WOT 8% of the time. It is not some weird average that requires plugging in the CAT ECM to figure out. Instead of pulling all kinds of information about offroad heavy equipment, pull out your manual on YOUR marine diesels, and tell us what it states.

The cummins literate state continuous operation at 80% load or less. NOBODY pulls the average and does math. Rated Cruise is 80% load all day.......... same with MAN, Cummins, Yanmar and others. Volvo rated cruise is 90% load.

I think most of what your saying is correct. But not #2. The 100% load is strictly limited running time for E rated engines - thats because it is quite hard on the high horsepower version E rated engines. Huge cylinder pressures etc. at WOT. So to be able to run 100% load all the time you need a A rated engine, which in the case of a C18 is in the 500 to 600 hp range. The E rated C18s are 1000 to 1150 hp. These have 30% load factor limits because they run at higher power ratings when in the 70 to 100 percent range.

I think the engine internals are quite similar for the different rated C18s. Running a 600 hp A rated version at WOT non-stop for 10,000 gals of fuel is much easier on the engine than running a 1000 hp E rated for 10,000 gallons continuous full power. Thats why they limit full load on D an d E rated engines - they have much higher power outputs for the same basic engine.

Otherwise what you wrote looks fine. Of course, you must have cooling systems and aftercoolers etc. all running perfect to run ay 80% load and achieve acceptable engine temperatures.

The fact that a high horsepower diesel engine will last 10,000 hours in a recreational vessel speaks volumes. That being said #2, no your thinking is wrong. The higher HP versions are only rated to run WOT for a shorter period of time, NOT continuous duty like a de-rated C18. Major is in total hours OR total fuel burned. Just run the motors how you use your boat and stop over thinking it.

IF you maintain your engines properly (by the book), you won't have any issues keeping proper temperatures running 80% load, or even WOT.

I was on my boat this past weekend and went through my CAT C18 manuals and the guidance is as I posted above. These are the standard factory manuals. The images below all came from the factory C18 manual:


As we know these are E rated high performance diesels. The factory guidance is that they may be operated at a load factor up to 30% or up to the rated load for 8 percent maximum of the duty cycle. The service schedule is based on total service hours or total fuel burned:


There is NO mention in the operations and maintenance manual anywhere that says you can run at 80% load factor all day long. In fact the factory manual specifically lists recommended cruising RPMs which for the E rated 1015 and 1150 hp C18 engines is 1900 RPMs for cruising. In my 68 Viking Princess, 1900 RPMs is about 67-68% load factor.



If all systems are operating properly, then you should be able to run at 80% load factor all day without blowing the motor up quickly, but you will significantly reduce your engine service life. As an example if you run at 25% load for 1 hour getting in and out of port and run at 80% load for 7 hours, that gives an average load factor of 73%. This is a 36.5 gal/hr average fuel burn compared to 15 gal/hr average you will see at 30% load factor. (This all assumes 50 gal/hour per engine at WOT) Running 80% load factor in this way will REDUCE your major overhaul service schedule from 10,000 hours to 4,100 hours.

That is the issue with running 80% load most of the time, even if the engines are running and serviced properly, you significantly reduce the engine lifetime.

It's crazy to think that micro managing your throttle use a few RPM either way is going to mandate a major at 4k versus 10k hours. This just ins't reality, to me. These engines are designed to over perform the recommendations. They just want to be cared for with proper fluid changes and reasonable throttle management. If you run the boat at what turns out to be an 80.1% load factor as opposed to a 74%, you shouldn't expect them to blow apart, nor should you anticipate the major service life to fall so abruptly. If an engine is going to crater at 4k hours, there is another issue at play, and your load factor be damned.

Take care of the engines. They'll very likely take care of you. No slide rules required.

I think you missed the point of my comments above. It is not so much the difference between 80% and 68% but running for example 7 of 8 hours at 80% vs 2 hours at 80% and 6 hours at 20% are very different average load ratings and average fuel burn. The CAT 10,000 hour major service interval is based on a 30% average load rating. That is much closer to 2 hours at 68% and 6 hours at 20%.

Again, these are only 10,000 hour engines if used close to a 30% average load rating. The CAT guidelines are 150,000 gals/10,000 hours which is 15 gal/hour. At 80% load that is 40 gal/hour so your engine lifetime will be much less.

NO, the 10,000 hour service life is based on 10,000 HOURS ONLY, or 150,000 gallons of fuel. It says "OVERHAUL CONSIDERATIONS". There is nothing else stated. You are reading into this, something that is simply not there. OVERHAUL CONSIDERATIONS means, a tech will look at the engine and determine how much life is left in it before it NEEDS an overhaul, based on compression and how it's performing. It may go another 5 or 10,000 hours. The manual has been updated since yours was printed and cruising speed is based on load which is a better determination of how hard the engine is working.

When you look at the ECM print out of about every yacht like yours, over 70% of the engine hours (if not 80%) will be below 1000 rpms or 8 gph. Think about all of the time idling at the dock, slow speeds in and out of harbors, slow speeds in ICW etc. 1015hp C 18's burn around 37 gph at 80% and 1150hp burns around 43 gph at 80%. Not to mention 98% of the yachts like yours, the engines will NEVER reach 10,000 hours of use in the yachts life. 150 hours a year, 10 years = 1500 hours. That's 66 YEARS of normal yacht usage. 100 engine hours of usage per year would take 100 years to reach 10,000 hours.

The majority of yacht engines will not last that long due to mis-use (too much idling, not running often enough) or poor maintenance (usually a blown hose, bad impeller etc.) that causes a catastrophic shut down.

The following is a direct quote from a 2008 thread between Marmot and K1W1, who has not been around in a while but was a respected member here and a proper marine engineer and ship engineer. He is saying exactly what I am saying.

https://www.yachtforums.com/threads/calculating-engine-load-factor.8661/

From Marmot in 2008

Caterpillar E rating: High Performance - For vessels operating at rated load and rated speed up to 8 percent of the time, or one half hour out of 6, (up to 30 percent load factor). Typical operation ranges from 250 to 1000 hours per year.

Refer to the fuel burn spec at 100% load at each RPM. The LOAD FACTOR is the actual fuel burn divided by the maximum rated fuel burn. If your engine is rated to burn 100GPH at WOT and you are burning 30GPH, 30/100= 30% load factor. This doesn't mean you are limited to never pulling more power out of the engine, it just means that you are limited to full rated power for 30 minutes out of every 6 hours and over the life of the engine and the amount of fuel burned should not exceed 30 percent of what it would have burned if it had been running at max rated power output.

In a nutshell, an engine has a lifetime that can be measured in weight of fuel burned. You can run that weight of fuel through the engine in a short time period if you are extracting large amounts of power, or you can take forever to burn that much if you only extract small amounts of power. The load factor represents the relationship between fuel burn and the number of hours you are taking to burn it.

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Every technical discussion with you turns into a pissing match. My entire point here was to discuss and disagree with what you said in post #26: "What you posted has nothing to do with load at cruise or continuous load and CAT does indeed recommend 80% load as an all day, every day, cruise speed for the C18 and most all other E rated CAT marine diesels."

CAT does NOT recommend ALL day EVERYDAY at 80%. They recommend a 30% average load factor to get near 10,000 hours. Because they have a standard fuel burn of 150,000 gal for when overhaul considerations need to be evaluated, simple math tells you that number is based on the total gallons divided by hours which is the definition of average load factor. Read what Marmot wrote above closely.

Also your comments about idling around on the ICW 70 or 80% of the time is correct and again is the point to be made. It is not 80% all day but incudes lots of duty cycling at lower speeds and low load ratings.

I have done engine start ups and required seatrial on well over 100 sets of new CATs with many different CAT technicians as well as higher ups from CAT, mostly for well respected large scale Yacht Builders. I've also been the Captain that CAT used to set up the joystick parameters or fine tune them for a few new yacht models for yacht manufacturer(s) for the CAT 360 system. I am very well versed in what CAT engineers want and don't want in regards to their engines, from the CAT engineers and top technicians.

The entire discussion was Caterpillars rated cruise speed when at cruise and this is someone else's thread searching for answers to his propeller situation AT CRUISE RPM's IE 80% load or 1900 rpms or betteron a set of 3406E 800HP engines, not your thread, which is indeed 80% load (the answer the OP was asking about). 80% load is where CAT allows them to be run all day, such as if you are delivering the boat in the ocean from one place to another, unlike say WOT which can only be run for an hour at a time, or 30 minutes depending on engine. It can be run anywhere else under that as well. But if you blow a motor and they see in the ECM printout that you've been cruising the engines at 85% rated load when you do cruise them, or the engines are never run above 40% load, your warranty is not covering it. There is absolutelty NOWHERE in the CAT display that will show you as an owner what your average lifespan load is, nor is CAT concerned about it as far as warranty goes. No yacht ever runs at cruise rpms all of the time, so the overall load works out usually to much less than CAT asks anyways. You're reading from the CAT manual, but not totally understanding what you're reading.