At sea patrol boat loses a little time in Welsh seaside town (4,6)
I believe the answer is:
'welsh seaside town' is the definition.
'at sea patrol boat loses a little time' is the wordplay.
'at sea' is an anagram indicator.
'loses' indicates named letters should be taken away.
'little time' becomes 't' (abbreviation for time).
'patrolboat' with 'a' removed is 'ptrolboat'.
'ptrolboat' is an anagram of 'porttalbo'.
'in' is the link.
(Other definitions for port talbot that I've seen before include "Welsh industrial town" , "South Wales town" , "Welsh steel town" , "Port, town in S. Wales" .)