[Wasted Income]

Originally Posted by houstonshark

Most boats have paddle wheels that measure the water speed (which can be inaccurate on a river) and/or GPS based speedo's.

Yea some do. My current offshore boat has both a pitot tube speedo and GPS into the chart plotter....neither of which are inputted into the engine ECUs. Houstonshark brought up a good point that paddle wheel and pitot tube speedos read differently if you are running with or against a current. The engine does not care how fast the boat is moving, as it is irrelevant to the load on the engine. Also prop slip, hull design, trim angle, and tab position can all play into how "fast" you are going vs the engine rpm or engine MAP (load).

I tuned my old LSx jet boat with a manual trans segment in the ECM. It was one of the easiest tunes I've ever done, as there is no transmission, and you never go up or down hill, so the RPM vs MAP is one straight angled line, basically a 2D map, versus a true 3D map like in a car.