Since my profession is lubricant sales, I’ll add some general comments to this thread: API (American Petroleum Institute) SN is the latest spec for gasoline engines; then you choose the 15W-40 viscosity. Since ski boats idle too much and throttle too much, both create fuel dilution even in the latest engines. Fuel dilution in the crankcase pulls the oil’s viscosity down, thus don’t use anything lighter in vis than a 15W-40 unless maybe a synthetic 5W-50 that meets API SN. To summarize, no 10W-30, 5W-30, or 0W-30. Last, I’m not sure if all synthetics do well with the chemical mixtures of fuel with their base oils, additives, etc. That said, ski boats are not a good place to push for extended drains. Change it at 50 hours.............engines aren’t cheap. I have an oil analysis from my 2017 Nautique. I’ll look it up and try to post it in a later thread.