Roman Catholic in small boat off the Sussex coast? Speedy vessel (10)
I believe the answer is:
hovercraft
'roman catholic in small boat off the sussex coast?' is the definition.
I can't judge whether this definition defines the answer.
'speedy vessel' is the wordplay.
'speedy' becomes 'hover' (I can't explain this - if you can you should believe this answer much more).
'vessel' becomes 'craft' ('craft' can be a synonym of 'vessel').
'hover'+'craft'='HOVERCRAFT'
Can you help me to learn more?
(Other definitions for hovercraft that I've seen before include "cushioned transport" , "Skirted vehicle" , "Vessel" , "cross-channel transport?" .)