Cannon right next to second sailor (6)
I believe the answer is:
mortar
'cannon' is the definition.
(mortar is a kind of cannon)
'right next to second sailor' is the wordplay.
'right next' becomes 'r' (I've seen this in other clues).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'second' becomes 'mo' (both are short periods of time).
'sailor' becomes 'tar' (tar is a kind of sailor).
'r' put after 'mo' is 'mor'.
'mor'+'tar'='MORTAR'
(Other definitions for mortar that I've seen before include "Bomb-launching gun" , "Used in building a house - or to destroy one" , "Brick bonder; weapon" , "Small cannon or building material" , "Masonry bond" .)