But if you use mineral oil, you could change it every 15 hrs and it will save you money while having more frequent looks at the oil. Synthetic oils last a long time, but in a boat, too
much can go wrong with the oil between the longer periods of the synthetics. Maybe I'm overly cautious, just that I've lost rod bearings and main bearings far to often because I didn't pay close attention to what the oil was telling me.