Next on the list of factors is pressure. When you increase the surrounding pressure, you can usually dissolve more gases in the liquid. Think about your soda can. It is able to keep the fizz inside, because the contents of the can are under higher pressure.
Assuming a prop, it depends on how you are propped but with a redline of 6000 rpm, most outboards perform best with a cruise in the 4000-4400 rpm range. If you want top fuel economy, get a floscan or such and see what is the most efficient for your engine and prop.
Bass boaters and other high performance enthusiasts are always looking to obtain the maximum performance out of their rigs. Whether trying new props, changing the boat and motor set-up, or by re-distributing the load, a go-fast boater is forever reaching for that last mile-per-hour of speed. Outboard motor gearcases come in all styles, sizes, and ratios depending on the motorâs attainable speed, horsepower, and type of usage. It is important for the savvy boat owner to know the gear ratio of his motorâs lower unit for propeller speed and efficiency calculations.