Oil Changes on long cruises

[SunFish]

We changed the oil in SE by using a little hand pump to pull the oil out of the dipstick hole. We had to bring the used oil oil back with us because we had trouble finding a place that would take it. It was very easy and no oil went into the water.

[ppriest]

Here's a tidbit which may provide some enlightenment - my recently acquired '02 Tahoe is equipped with an engine monitoring computer which displays from time to time the message, "Engine Service Required". The explanation provided in the operator's manual says something to the effect that the system now has the capacity to keep track of several applicable parameters from which it determines when it's appropriate to change the oil. While unstated, my guess is that those parameters include such things as total operating hours since last reset, operating hours at normal engine operating temperature (derived either from the coolant temp or an oil temp sensor), perhaps some record of hours operated in lower gears as a measure of loading, etc. In any event it's conceivable that Chevy feels comfortable in predicting the useful life of the lubricant based on some actual operating conditions.
This speaks to the generally high level of lubricant quality commonly available these days. It aligns nicely with the trend toward longer and longer oil replacement intervals in auto engines.
There is also the common belief expressed in several of the other posts that operating any engine for extended periods where the operating temperature stabilizes and persists long enough to volatilize any moisture and acids accumulated in the oil yields the best service life of both the oil and the engine generally.
Given the foregoing I feel comfortable running my CD22 with a single BF90 well beyond the manufacturer's recommended 100 hour change interval PROVIDED I don't permit the engine to sit unused for extended intervals within the period AND I religiously check the level and appearance of the oil on the dipstick topping off whenever indicated.
Since I'm coming to boating following quite a number of hours operating behind light aircraft engines where it's routine to check the oil before every flight and also to monitor the oil temp during each flight, it's really no big adjustment for me.
I'm thinking that, when my Honda goes out of warranty, I'll switch to a synthetic to see if I can detect any difference.

Paul Priest
Sequim