Brian says:

...or am I weaseling out? :-)

;-)
Nope! There _are_ very, very small effects at the surface that can "mimic"
compressibility (hence the really small Mach number used. Also, the speed of
sound in water is WAAYY higher than in air, I want to say in the order of 1800
ft/sec but I may be way off. It's faster - 'nuff said ;-)

So "Yes" there can be some effects, but it's a tough call, and if not actually
at the interface, it is best to zero out the Mach no.

Steve "dang, I feel technical today"
Stephen C. Baker - Yacht Designer
http://members.aol.com/SailDesign/pr...cbweb/home.htm