Small mat for ship (7)
I believe the answer is:
coaster
This clue is a double definition.
'small mat' is the first definition.
(I've seen this before)
'ship' is the second definition.
(coaster is a type of ship)
'for' acts as a link.
(Other definitions for coaster that I've seen before include "Mat for decanter or glasses" , "Small mat for glass" , "It goes under a schooner, perhaps" , "on which some mug may be made to stand?" , "... another one [VESSEL]" .)