Glide over water with double force in small boat (5)
I believe the answer is:
skiff
'small boat' is the definition.
(I know that skiff is a type of small boat)
'glide over water with double force' is the wordplay.
'glide over water' becomes 'ski' (as in water-skiing).
'with' is a charade indicator (letters next to each other).
'double' shows that letters should be duplicated.
'force' becomes 'F' (symbol used in Physics e.g. f=ma).
'f' duplicated is 'ff'.
'ski'+'ff'='SKIFF'
'in' acts as a link.
(Other definitions for skiff that I've seen before include "Light rowing boat for one person" , "Small rowing boat" , "Small light boat" .)