Mr. Steve... you are talking about some boats and some installations, coupled with a whole lot of ASSUMEtions. That is a recipe for disaster or at least problems. The boat may be designed to all kinds or standards. That is no reliable path to insure the group that comes behind will maintain those standards when they shove the generator into the boat to meet a marketing requirement. A quick review of the installation manuals of most smaller lower cost diesel generators will show the units are designed to never have the exhaust underwater. Many of the BVI charter fleets heel to the point or have wave action above the exhaust level. In the simplest of arguments while most gensets are set up to shut down on their own at the sign of danger. The panels are set up so that most crew members will not hear any of the alarms from the generator while underway. The reality is most of us underway will not know the generator has any issues until it is too late and real damage has been done. All that said... many treat the generator and AC just like the one in the hotel. They turn it on when they check in and never turn it off. Next time you are dingying around the anchorages. Note the boats locks up with exhaust coming out. In much simpler terms if the single exhaust is any where near the water line. There will likely be issues in some sailing conditions running the generator underway. There is no simple way for most users to determine by sight any vacuum issues with the intake underway.