Engine Choice: cat v Cummins

Hi,

I don't have any experience with "modern" Cummins so my answers might be a bit biased.

I see that the 705 mhp/526 kW claimed for C 12 Engine is for an E Rated Engine.

The Caterpillar E Rating is the highest performance one they offer.

This rating is typically used on vessels operating at the rated load and rated speed up to 8% of the time or 1/2 hr out of 6, ( up to a 30% load factor)

Typical operating hours are seen as 250 to 1000 a year.


I found a QSM 11 Online with 715 Hp and also shown as 526 kW so they are both pretty close in output.

This configuration is shown as an HO or High Output Engine, as such Cummins describe it's typical operation as this:

High Output (HO): Intended for use in variable load applications where full power is limited to one hour out of every eight hours of operation. Also,
reduced power must be at or below 200 rpm of the maximum rated rpm. This power rating is for pleasure/non-revenue generating applications that
operate 500 hours per year or less.

I also see that the Cummins is limited to 250mm of Exh Back Pressure where as the CATS can typically deal with twice this amount.

Both are good pedigree manufacturers and there will be folks that swear by each one over the other. It is a case of deciding what is best suited to YOUR needs and requirements.

Spend a bit if time and do a bit of googling for Cummins QSM 11 Failures/Faults/Problems - / is used to indicate a change of search string not just one big long one.

Do the same for CAT - It will stop you getting too bored on a cool winters evening in Sydney

Engines

Worked on Cat gear most of my life and found backup was fantastic from Cat dealers all around Australia and any problems were fixed asap,spares always available promptly and service network was amazing even if sourced outside Australia.Very little to do re Cummins. Snake.

I suggest that you research the service dealers in your area. Find out who will do warranty and service work at your home port, or in the area where the boat will spend some time. Talk to the dock master, brokers, service managers, and other boat owners to get some unbiased opinions of the service in your area for both CAT and Cummins.

If I may add my 2cents worth, choose the one with the least amount of stupid, stupid electronics on either brand.

As a main dealer of another major brand, nothing is more time consuming, expensive and downright useless than bloody electronics on an engine.

AAaaarrgghhh!!!!!!

Rant over and a bit of steam let off.

Can you tell what I've been working on for the last week?

Take your pick. Volvo have no shortage of electronics; ran a new MAN recently whose display had me scratching my head. And the list goes on. It will soon be necessary to hire a factory rep as well as a captain to leave the dock. God help the engineers. They'll soon be brand specific. In fact they may already be to some extent.

Sorry if these questions are really basic, but can someone explain exactly what this means? Am I correct in assuming that this means you can run the engines at max rpm for 30min out of every 6hours? And what does "rated load" and "rated speed" mean?

Thanks!

Rated load is the maximum power approved by the manufacturer when the engine is turning at the rpm at which that output was produced on the dynomometer.

RPM and load are directly related in a marine propulsion appllcation. That relationship is illustrated by the propeller curve. If the engine was driving a generator or other constant speed device, the rpm remains constant across a wide range of loads so rated load and rated speed occur at only one spot, 100kW at 1800 rpm for example for a 100kW generator.

The ratings people are talking about here are "load factors." The same basic engine can deliver a wide range of power. For example a CAT C18 is rated to produce anywhere from 454 hp to 1001 hp over a range of rpms from 1800 to 2300.

That engine can operate continuously, non-stop, for thousands of hours producing 450 hp @ 1800 rpm. That is 100 percent load factor, CAT's "A rating."

You can pull 500 hp out of it at 2100 rpm for about 80 percent of the running time at the B rating. That means that for a few hours each day it will run between low power and full power while maneuvering or other reduced power activities.

At the E rating you asked about, you can pull 1000 hp out of it at 2300 rpm but only for occasional short bursts of speed.

The fuel controls and governors will be setup to match the maximum rated output. The only thing you can control once the engine is properly matched and installed on the boat is how long you spend at full rated power and that is the third part of the equation, time. Part of the reason for the reduction in time allowed at higher power is heat rejection of the engine components themselves, and dynamic loads imposed by the weight of parts slinging around. Very hot heavy parts moving at high speeds under high cylinder pressures will fatigue faster than the same cool parts loafing along under low pressure.

Another way to look at it is that engines are kind of like lifestyles, fast and furious doesn't last long. An engine is capable of burning just so much fuel in its lifetime, and if it sips it gently it will live a long, unremarkable, and troublefree life. If it gulps it in great quantities very rapidly it will make a great deal of noise and heat and it will do amazing things before it dies at a young age.

Although I dont disagree with anything the previous poster said, I will try to put it in simpler or more practical terms.

An E rated engine is rated for up to 30% load factor. Most engine manufacturers base load on fuel consumption. So over an extended period of time the total fuel burn should not exceed 30% of maximum fuel burn at rated WOT, a number provided on the HP/fuel consumption vs RPM prop demand curve.

I personally like the CATS over the Cummins QSM11's. Although the QSM11's are good engines too. Cats dealer network is larger and the maintanence items are much cheaper.......I just did a service on a set of qsm11's and the oil filters, fuel filters, zincs etc etc all of the maintanence parts were a fortune compared to CAT's......

IMHO From one who has worked on all of these engines. I would opt to have Detroit Diesel S-60. if possible. Simpler to work on, the electronics have been around longer than both Cummins or Cat. Parts are less expensive and general maintenance is less costly IMHO
Thanks Jim

I have a boat that I manage with series 60, the 825hp ones. Overall they run nice and are quiet. It cruises at 26 knots at 80% load, and it has torque at idle speeds, but over that it's not nearly as torquey as the cats. Weight makes a big difference in the load factors versus rpm (we're talking about a few thousand lbs in a 55 express, 80% load with 1/2 fuel (350 total gallons)would be say 1890rpms, 80% load with full fuel(700 total gallons) 80% load is 1820 rpms). They have run good, but both aftercoolers were leaking as were the intake gaskets, at 250 hours and 2 years old. Warranty repairs were covered but you always have to go through some nonsense to get them done. They have to take pictures, e-mail so and so, wait for a response, and a whole week goes by, and then they have to come back out and do the work when they can re-schedule it, it's a PITA. Whereas with CAT the mechanic is out, he calls his boss, they approve it, and he continues to do the job and gets it done. I haven't seen maintanence any cheaper then the CATS, comparable I would say.