His map set out passage in the middle for vessels (10)
I believe the answer is:
steamships
'vessels' is the definition.
(steamship is a kind of vessel)
'his map set out passage in the middle' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'in the middle' indicates the central letters.
The middle of 'passage' is 's'.
'his'+'map'+'set'='hismapset'
'hismapset' anagrammed gives 'steamship'.
'steamship'+'s'='STEAMSHIPS'
'for' is the link.
(Other definitions for steamships that I've seen before include "They'll want a port" , "Vessels with funnels" .)