Mercs and megaphones--thinking the unthinkable?

[OUTBOARDER]

The basic physics relation (Drag proportional Velocity squared and Power proportional to Velocity cubed) I stated still applies, it's the K that is variable with different conditions of boat operation. You stated that "The boat is dragging less in water" which is contradictory to what I stated in my posts above and implied when using the formula that "all else remaining constant". "K" is NOT constant. The calculated value based on a single velocity and Hp was used for the increased Hp to estimate velocity to keep consistent with your approach. There are many variable conditions going on to apply a single K value to all operation conditions.

Relations noted here (K usually known as Cd - coefficient of drag):

http://en.wikipedia.org/wiki/Drag_(, physics)


Examples for drag and power (air drag used here but same applies to water drag and Cd still not constant but used that way for easy relative to compare calculations)

http://phors.locost7.info/phors06.htm

Let's get this post back on track regarding megaphones!

once again for planing hulls that run high speed = k * sqrt of hp
more than one boat builder has used it to predict speed of a boat for a change in hp

let me go one step further with my real life john boat experince
15 hp = 25 mph
25 hp = 36 mph
50hp = 44mph over powered Carolina skiff J16 with 1998 Johnson 50 hp went 44 mph

as in real life John Boat example
k can be treated as constant over a small interval

the cubed HP is for Discplacement hulls like Ships.