For a boat engines (outboard, gas inboard, or diesel), probably annually or every 100 hrs, whichever comes first. If you put your boat away for winter, change oil when it goes for storage, not in the Spring. Some opine every 200-250 hrs.
For cars, it depends... When Should You Change Your Oil? Follow this simple guide to keep your engine humming a happy tune.
How long does engine oil last sitting in the can? At least 2-3 years.