I guess the best way to find out is if we compile the data over a long period of time and see what we get. I'm not that familiar with marinized engines in these boats, no disrespect intended, I have only worked on them in the construction or mining environment. Now I sail on cargo ships so the engines are either medium speed or slow speed. I do know of a 3306 in a hydraulic crane in northern Illinois that I have personally serviced over the years and the owner is meticulous about preventative maintenence. There are a whopping 62k hours on this engine. This engine drives the machine from site to site and operates the hydraulics for the crane and stabilizers. The operator/owner says he runs the engine at full throttle all the time the impliments are being used and won't idle for more than fifteen minutes, and has done so since he bought the crane new thirteen years ago. I also worked on a D-11 dozer for Cat in a mine in Arizona with 29k hours on it and the engine was a 3512. Same thing, run at high RPM as much as possible. As many have said, there must be something to the design specifications that allow for the lower RPM's and operating loads when the engine is intended to be marinized. Since my wife and I are looking for a Trawler I am really interested to see how all of this works out. Thanks to all for the great input and keep it coming. I have so much to learn about these boats and look forward to it.
*Don't know if it's true, but an engineer here in Seattle I spoke with said he worked on the original design team for the 3306 when he joined CAT out of college.* One of the design briefs was to build an engine that could operate in the extreme cold of the North Slope, which meant long periods of idling followed by long periods out maximum output running dozers, excavators, etc.* Maybe that is why they work out ok for marine engines.* He also said he saw a lot with 50,000 hours on them.
I don't think that modern engines are built to do this.*