What sounds like protective layer in ship (6)
I believe the answer is:
barque
'ship' is the definition.
(barque is a type of ship)
'what sounds like protective layer' is the wordplay.
'what sounds like' shows a homophone (sound like).
'protective layer' becomes 'bark' (protective layer on a tree).
'bark' sounds like 'BARQUE'.
'in' acts as a link.
(Other definitions for barque that I've seen before include "Small ship" , "Sailing ship" , "Three-masted ship" , "sailing-ship" , "Sailing boat" .)