Islander
What I originally posted, and Dave seconded, is quite true and ia a very important concept for operators who are trying to minimize their wake. So, let me try to explain again, more clearly (though the physics class I learned it in was a long time ago
. My appologies to any physicists for over-simplification and leaving out the math - it gives me a headache.
)
A boat in motion has two possible modes of operation; i.e., displacement and planing.
At slow speeds, a boat is operating in displacement mode (so named because
it's sitting down in the water and displaces [pushes aside] the water through which it moves.
In displacement mode, a boat makes two waves, one at the bow and one at the stern. (More about this later.)
In displacement mode, the faster the boat goes, the more water it displaces, and the bigger the wake it leaves.
That remains true until the boat reaches what's called "hull speed", which is the fastest any given hull can go and still operate in displacement mode.
Now, any boat's "hull speed" is governed by the distance between the bow wave and the stern wave; the greater the distance between the waves, the faster the boat can go and still be in displacement mode. (That's why the Mount's wake got smaller after she was lenghened.)
For a displacement type hull (think large-ish sailboat), hull speed is all you can ever reach because of the hull shape. Pour in extra power, the hull just squats lower, more water is displaced, and its wake just gets bigger. I've seen a movie of an experiment demonstrating this. A big sport-fisherman was towing a good sized sail boat using a special harness; it was pretty amazing!
With a planing hull (most power boats), that's not the case because planing hulls have flat surfaces at the stern.
A boat with a planing hull, after it reaches hull speed, actually climbs up over its own bow wave and skims over the water on those flat surface I mentioned. Since less of the hull is in the water at this point, less water is being displaced and the wake size is reduced.
There's typically a pretty wide range between "hull speed" and "planing speed" (the lowest speed it can go and still skim over the water on those flat surfaces). For instance, on my boat hull speed is about 7.5 mph, and "planing speed" is pretty close to 20 mph. Even then the boat's not riding as high as it can, and is making a bigger wake that it would at higher speeds.
Now, here's the rub.
As a planing hull is going from "hull speed" to "planing speed", it's squatting low in the water and pushing the biggest wake that it possible can (and burning gas in painful quantities.)
So, the upshot is that the longer the boat takes to accelerate to "planing speed" the longer it pushes the biggest wake it possibly can.
And, believe me, an under powered boat can take a long time to accelerate to "planing speed", or maybe never get up to where it's making the least possbile wake.
All of which is why I stated that horsepower limits can be counter productive to minimizing wake.
Sorry for the long post, but boat operators need to realize that the faster they can get up on a good plane, the better it is for everyone concerned.
Silver Duck