The behavior of air cavities formed in the tip vortex trailing from re
ctangular and elliptical planform hydrofoils has been examined both th
eoretically and experimentally. These cavities have some peculiarities
, in particular their ability to move upstream and reach a stable posi
tion near the hydrofoil. Detailed measurements of the the velocity com
ponents and the cavity characteristics have been made. The results are
compared with the predictions of a theoretical model based on the equ
ilibrium balance of a cavity developing in a Lamb vortex.