Propping for WOT and 80% cruise

rtrafford · Nov 13, 2025 at 9:05 AM

Capt J said: ↑

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.
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....and by all means, run your Cats the way that you see fit and proper to do so. You don't need anyone else telling you how to manage your systems. As a very basic rule of thumb that does not apply to DDEC's, as you advance in running time beyond 3-4k hours on any machine, you should be monitoring oil sample reports, exhaust temps, oil consumption, sounds, etc. The assembly of these points of data will help the engine speak to you in terms of when it wants a makeover. There is no magic litmus in a handbook by which to live. Two engines from the same factory run that have the same type of use and care will respond in their own way regarding longevity. For instance tomorrow morning your starboard engine could lose #1. Meanwhile Port might be just fine pushing you along for another 1500 hours.

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Propping for WOT and 80% cruise

rtrafford Senior Member