Re: Frequency of Changing Oil & Fuel Filters
"Westerbeke Corporation for example specifically says that synthetics do not change the intervals at which you change the oils."
Westerbeke can't actually make any blanket statement about oils, since they don't actually make engines. They assemble blocks and other parts contracted from the lowest bidder, and those actual makers have varied over the years.
Westerbeke are also the technically astute folks who paint the entire assembled engine a nice shiny red. Including the belts and hoses, whose makers expressly say NEVER to paint them, and to condemn them if they are found painted.
40-50 years ago, the concept of changing the oil during layup, to prevent acids from eating the engine, might have made sense. But modern oils with modern additives pretty much counteract all those nasty contaminants, and continue to do so for long periods. Take a look at any premium full synthetic oil, odds are the oil change interval is spec'd for something like ONE YEAR or many thousands of miles.
I'd strongly suspect that means the contaminants, including acids, are being neutralized and rendered safe for a full year, too. I'm sure those oil companies would have some direct comment on the matter, although fear of litigation probably would have them say "follow your engine maker's recommendations" unless you asked precisely the right question, i.e., how long do your additives perform?
I'd be more concerned with changing the oil in the spring, pre-launch, to get rid of the large amount of condensate that will have formed in it over the winter. Of course you could certainly just drain the oil in the fall, leave it empty (with a warning tag!) and put in new oil in the spring, but leaving the old good oil in the engine would probably cause less damage than letting condensate build up alone, wouldn't it?