On Sat, 21 Mar 2009 23:43:31 -0700 (PDT), Monkey Butler
wrote:

On Mar 22, 12:26*am, Wayne.B wrote:
On Sat, 21 Mar 2009 18:00:36 -0700 (PDT), Frogwatch

wrote:
why does a boat make a stern wave?

Not very scientific but I view it as sort of a rebound effect as the
water that has been displaced downward by passage of the hull, now
springs back up behind the boat and overshoots the surface due to
inertia.

Hope this isn't a double post, Goggle Groups is a PITA


Wayne, this is true but you can’t concentrate on just the stern wave.
Any time you disturb a fluid you will transfer the energy via a series
of waves. Drop a stone in a pool, does it create just one wave? No,
and neither does a boat hull.

I find it fascinating to observe the “wake” left by a small duck
paddling along in glass smooth water on a calm morning. If you look
at the total amount of surface area that he can affect it is amazing
considering his size and weight. If he swims by another duck then that
duck will bob up and down in his wake so duck number two must be
absorbing the wave energy that duck one put into the water, right? But
if duck one paddles through a flotilla of one hundred ducks they all
bob up and down. Go figure.

It's classic harmonic oscillation and wave propagation. The first
rebound creates the first wave, displaced water over shoots and
creates the second wave, etc. Since it is a damped oscillation,
limited by the viscosity of the fluid and energy imparted to the wave
train, the number of waves created is relatively small.