Knots sailors try to avoid (5)
I believe the answer is:
reefs
'try to avoid' is the definition.
I can't tell whether this definition defines the answer.
'knots sailors' is the wordplay.
'knots' becomes 'reef knots' (reef knot is a kind of knot).
'sailors' becomes 's' (this might be a standard abbreviation I've not previously seen).
'reef'+'s'='REEFS'
Can you help me to learn more?
(Other definitions for reefs that I've seen before include "Submerged ridges of rock or coral near the surface of water" , "coral banks" , "Groups of submerged rock" , "Ridges of rock or sand beneath sea surface" .)