Take no notice of one rig at sea (6)
I believe the answer is:
ignore
'take no notice of' is the definition.
(to take no notice of something is to ignore it)
'one rig at sea' is the wordplay.
'at sea' indicates an anagram.
'one'+'rig'='onerig'
'onerig' anagrammed gives 'IGNORE'.
(Other definitions for ignore that I've seen before include "Disregard - cut" , "bypass" , "Pay no heed to" , "Walk away from" , "Spurn" .)