Close to mine in his sampan, exercised nautical skills (10)
I believe the answer is:
seamanship
'skills' is the definition.
(I know that seamanship is a skills)
'close to mine in his sampan exercised' is the wordplay.
'close to' suggests the final letters (the close of something is the end).
'in' is an insertion indicator.
'exercised' indicates an anagram.
The last letter of 'mine' is 'e'.
'his'+'sampan'='hissampan'
'hissampan' with letters rearranged gives 'samanship'.
'e' going within 'samanship' is 'SEAMANSHIP'.
'nautical' is the link.
This may not be right. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for seamanship that I've seen before include "Skill of a sailor" , "Sailing skills" .)