Should You Exercise The Kids

Can someone show me in an engine manual or manufacturer info where it says to run them at least a couple times a month or any similar info? If your conditions warrant due to bottom growth or other items I can see it but otherwise I see no validity in starting them every other week. There are millions of boats, cars and other internal combustion engines that are winterized and/or not ran for months at a time. Now I'm not talking about letting something for years. As we all know, if it rests, it rusts. But starting every other week? How long do you really think the oil stays up in the engine after you run it? Have you never heard that the most destructive time for an engine is at start up until oil pressure builds? Why keep doing this? What are you gaining?

I agree with you, DM. Does it hurt? No. But I don't see it as a requirement.
So if you live nearby and spend time on the boat, by all means start the boat and run it on occasion. But I don't see it a necessary to hire/recruit someone to do this if the boat will sit for a couple of months. I've been around larger boats with Diesel engines my entire life, and have never once had trouble with an engine that's been sitting idle (in the not running sense, running at idle is really bad for them).

The trouble is that all the information we have is anecdotal and originates in hearsay. Including my advice As Dockmaster says: Where's the documentation?
Some of us have some exposure to running take-out engines in storage that can't be turned over after extended storage as the rings are rusted to the cylinders. There's a thread on that on the gee captain forums that many engineers have weighed in on. That is obviously the extreme, but it illustrates the concern. It's not apples to apples, either, because those kinds of engines don't have exhaust systems attached.
There are many factors involved, starting with the design of the exhaust and how much water remains in the exhaust. Add environmental factors, and that water can saturate the air in the exhaust system to some extent. Capt J points out that some engines he had experience with developed compression issues in some cylinders. Light corrosion on cylinder walls can abrade piston rings. At least some of the "oil" on cylinder walls is diesel fuel, which, evaporates relatively quickly.
Winterization is an apples and oranges scenario, since there should be antifreeze in the exhaust as opposed to salt water. Besides, who doesn't stuff a paint bucket or ball into the exhaust outlets during storage?
As NYCAP asks, how long is a "few months"? Ultimately, there will be open intake and exhaust valves. From my experience and training, I can tell you that certain 4 cylinder engines will stop at one of two places in the rotation, and it's likely similar on engines with more cylinders.. Anyone who has ever replaced a ring gear or flex plate because the starter will do little more than "zing" , knows that the damage on the ring gear is in only one place on the flywheel/flex plate. Shut off engines stop in one place, more often than not, for some reason. Additional reading, for those curious.
Ideally, the engines should have a load, which is why one forward/one reverse is a workable compromise. Ultimately, even idle can't be too bad. Just walk around any truck stop at night, especially in the winter. Many idle for hours, with no more load than the alternator keeping the TV going. It keeps the fuel from gelling and prevents "non start" situations.
Google isn't much help when searching for reliable advice on this, at least not on the first page of hits. I'm not sufficiently invested in this to look further. I tried "running diesel engines periodically" and came up with a bunch of myth-buster stories in magazines, that didn't touch on the issue.

Gas engines get fogged. Diesel engines do not.

I don’t think the comparison to trucks at a truck stop is relevant. Most of those are running for heat, A/C or power inverters.
Again, my point was not about engines sitting for very long periods where rings adhere to cylinders. I was referring to the OP’s reference to a few months, maybe a bit more for longer winters. Seems silly to me to hire someone to start engines every other week. I think you run higher risk of the hired hand causing damage then from the engines sitting a few months.

Personally, I have never seen harm in exercising a marine diesel engine. Especially if the boat is planned to remain dormant a few months. Starting and running the main engines a few minutes monthly gives a you good overall on how the boat is operating as a whole, even if only dockside and testing gears / steering. You should also take the opportunity to check other systems and their functionality(not a bad idea for a laid up boat either).

Bit of experience from a different application but I feel this relates. While on trans Atlantic passages to the Med on any yacht we would have our cruising RPM for what was normally 10-15 days continuous run time(Many factors determining run time). Our RPM for 2500NM + voyages was generally different to short Caribbean jumps. Reduced by more than couple hundred RPM most of the time. If our distance to be covered exceeded 72HRs I would implicate increasing main engine RPM to 80% load for 20 minutes once a day. This was an effort to move the engines/gearboxes through RPM range during the pro longed lower RPM crossing period. Sometimes the exercise lasted longer than 20 minutes. Having not done that for 10-15 days continuous, 1000RPM, on a CAT3512 can have negative impacts over time.

As suggested previously, you are not creating more problems by starting and checking your equipment on a monthly or bi weekly basis. If anything it could alert you to a new issue that may have been a developing problem months/years! I've seen plenty of dockside beauty's go to leave port only to discover a maneuverability issue in the most precarious navigational situation, then disaster. Check your gear!