[oldbluesplayer]

hmmm, well, returning to the core of this post...

As most Mercruiser IO powerplants are GM, I would bet you could get the torque / horsepower / rpm curves from them - I know in my old hot-rodding days these numbers were available - and often were published in the factory shop manuals (not the owners manual), but the last set I have of those is for old Ford V-8's (think Boss 302.... yeah, I'm an old fart)

quite true on horsepower to get to plane, vs horsepower to maintain - same with a car, what it takes to accelerate to 60mph, vs, what it takes to cruise at 60mph - much lower.

Phnyx, sounds like you have heavy aircraft background - safety requirements called for many more guages to monitor in-flight condition of engine - on small, pleasure type boats you will mostly see fuel flow, maybe voltage, temp, oil pres if an inboard or IO - but would probably get more involved on a big bucks sportfish with diesels. My experience on manifold pressure, is only on piston engine aircraft, and military / commercial vehicles, with turbo or superchargers (and hot-rods with same)- so the boost point kick-in, and max pressure, could be monitored. Any other old farts out there, with any Army experience, remember the M551 Sheridan light tank - had a 6V53 Detroit Diesel, with twin turbos, and a supercharger - on full boost it was quick - I worked on that puppy at the Detroit Tank Arsenal.

stray thoughts...

Bill