I'm running a new charter boat that sailed about twice a week last season and I changed the oil every 100 hours. This season I'm running the engine about 30 hours/week sailing more like five days/week multiple times/day. i just changed oil and filters a hundred hours ago and it's only been a few weeks- oil is still clean and no leaks- can I get away with changing less often if it's running so much? I'm a sailor not a mechanic ;)
The owners manual has the following service recommendations.
If your engine has the shallow sump (oil pan), change the engine oil and filter every 150 hours.
If the engine is fitted with the standard sump, change the engine oil and filter every 250 hours.
These recommendations are for vessels that are in constant use like yours. Obviously engines that are only used very occasionally should have their oil and filter changed every year, no matter how many hours on them.