Proper Performance Engineering

[ThePHNX]

The Good, Bad, and Ugly:
Quote from Mercury Marine:
........ " How do I obtain horsepower curves, torque curves, or fuel consumption data?

Horsepower and torque curves are not published because they are considered confidential company information. Fuel consumption data is not published because it is affected by factors beyond our control, such as boat hull type, temperature, humidity, altitude, gear ratios, propeller, etc. In some cases, fuel consumption or other performance data is available from your boat manufacturer for a specific boat/engine combination."

What absolute nonsense, keeping torque diagrams secret. Did not know marine engineers were required to be all wet!-(

Anyway: to properly determine best props (wheels), throttle settings, etc. one NEEDS to know the engine dynamics and torque curves.

For instance, one post read recently said there was NO delta between 2 stroke and 4 stroke engines, ah but I beg to differ: and the difference is readily distinguishable when the torque curves are shown.

Some two-strokes are notorious for their icicle (stalagmite) power curves where there is hardly any power until a certain high point of RPMs and the power multiplies so rapidly it totally changes the engines personality.

Who here can at least help with engine RPM stats, High, low, and cruise (typically 75%).

The engine I'm working with is the Mercruiser GM I-6 165 I/O. Knowing the proper throttle / RPM settings (again, the POWER is a direct function of engine design, volumetric efficiency and RPM) and the planing speeds for the SeaCraft hull we should be able to compute the proper - theoretical - pitch and diameter. Once the design P & D are determined things like harmonics, slip, etc. would play into the final determination. Right now I find the five blade Hill <http://www.hillmarine.com/> interesting.

Thanks, HBH
Oh yes, the craft is a lovely 1976 SeaCraft SF20