Small boat, right at the back of the ship (4)
I believe the answer is:
raft
'ship' is the definition.
(thesaurus)
'small boat right at the back of the' is the wordplay.
'small boat right' becomes 'ra' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'at the back' indicates one should take the final letters.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
The final letter of 'of' is 'f'.
'ra'+'f'+'t'='RAFT'
Can you help me to learn more?
(Other definitions for raft that I've seen before include "Flat, floating platform" , "Structure made of timber" , "Flat floating craft" , "water transport" , "Simple boat" .)