Re: Drafting in Bicycles versus Boats

[John Denker <jsd@MONMOUTH.COM>]

At 11:03 AM 9/15/99 -0500, Joseph Bellina wrote:
> Who knows if this is the connection, but I recall a discussion which
> indicated that the water resistance of a ship decreases with length.

It's not the connection.

The hull speed of a boat (in knots) is 1.34 times the waterline length (in
feet).  This is, not coincidentally, the wave speed for a surface wave of
wavelength equal to boat length.  For a discussion, see e.g.
  http://boatsafe.com/nauticalknowhow/waves.htm

Hull speed is a powerful barrier for any boat that is supporting its weight
by displacement.  This is why sailboat races have "length classes" and
within a class the races are decided by such tiny time differences.

The physics here involves the dispersion relation for surface waves, which
is very soft (very low speeds).  There is no analog to this for submarines
or cars or bicycles.

Also note that hull speed is irrelevant for boats when they are in
hydroplaning mode (as opposed to displacement mode).