[ThePHNX]

Am familiar with this relationship.
Note that it requires knowledge of one or more performance values for the specific engine.
It does little for analyzing the best performance from a given engine.

For instance, a rule of thumb is that engines are generally most efficient at their 75% power settings. That 75% position is NOT linear.

Several things are known about vessel throttle/power management - whether aircraft or planing boat - the amount of power needed to get `on step' (and that phrase applies to a hull without a geometric step, as it does to an aircraft wing) is greater than the amount of power required to keep it there. The skilled pilot will back off throttle while monitoring speed as will the skilled helmsman. Advancing throttle(s) after getting `on step' may increase speed but disproportionately increases fuel consumption.
It is a given that aircraft manuals provide extensive information on the powerplant. It is a shame on the boating industry that these same standards are ignored.

Am wondering if some power boaters add engine instrumentation; vacuum, manifold pressure, fuel flow. I know that on my Snowgoose Motor-Sailer I found the fuel flow meter (costly because for diesels a return line is required) VERY useful.

Here's a question then: What kinds of engine instruments are some of you using, and how. BTW, had full manual from Volvo and it was excellent. Guess I'm as much a Volvo fan as I am a Merc' denigrator!-)

HBH