Oddly, boat lost a raft (5)
I believe the answer is:
balsa
'raft' is the definition.
(balsa raft is a kind of raft)
'oddly boat lost a' is the wordplay.
'oddly' means one should take alternating letters (letters in the odd-numbered positions are used).
'boat'+'lost'='boatlost'
The alternating letters of 'boatlost' are 'bals'.
'bals'+'a'='BALSA'
(Other definitions for balsa that I've seen before include "Lightweight timber" , "wood for raft" , "South American tree" , "lightweight boat-builder" , "Strong, light wood" .)