Cathy's all at sea in pleasure crafts (6)
I believe the answer is:
yachts
'pleasure crafts' is the definition.
(I've seen this before)
'cathy's all at sea' is the wordplay.
'all at sea' indicates an anagram.
'cathys' with letters rearranged gives 'YACHTS'.
'in' is the link.
(Other definitions for yachts that I've seen before include "Pleasure boats" , "Craft for 6 dn" , "Pleasure craft" , "Vessels propelled by sail or power" , "Light sailing-vessels" .)