Pat and I have discussed increased interval of oil changes, as well as options. My experience on that size block was with the 130 (different block and engine than the 150), and I felt that I was not able to get all of the oil out with vacuum devices. So I also went longer than the 100 hours when on long cruises. I don't know exactly how much oil I was leaving in--but felt it was over 10%. On the other hand, not changing the filter at the 100 hours, does leave some old oil in there also. One has a valid argument either way.
Honda's recommended way is to drain thru the plug in the bottom of the pan--.
Pat is running almost every day, most of the time at about 2000 RPM, only one start a day (starting is the hardest on the engine, because of lack of oil in all of the critical areas). There is no time sitting for long times for water contaminates. Pat is running the engine up to temperature. The Honda 150 is the Accord 2.4 Liter block--and that has oil change intervals from 3,000 to as much as 8,000 miles depending on driving conditions. The 2000 RPM with no high loads (like getting on plane) simulates the best conditions, and thus I estimate that this is about 200 hours on the automotive engine. On long passages where I have had tp run a diesel engine (running 24 hours a day at 1300 RpM (slow displacement speeds) I moved the oil change interval up to 200 hours--and as Brent noted, check the appearance of the oil)
With the 6000 miles of the loop this would be 1000 engine hours. Oil change at 100 hour intervals would be every 24 days! (Assuming 8 months to do the loop)
There are many industrial engines which run for years without shutting down for an oil change--they use huge filters on the oil, and a little is replaced at a time.
