Aboard ship, decorator without a harnessing line shivers (9)
I believe the answer is:
splinters
'harnessing line shivers' is the definition.
I can't judge whether this defines the answer.
'aboard ship decorator without a' is the wordplay.
'aboard' means one lot of letters goes inside another.
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'decorator' becomes 'lint' (I can't explain this - if you can you should give a lot more credence to this answer).
'without' is an insertion indicator (some letters go outside or 'without' others).
'a' becomes 'per' (eg 'one a day' means 'one per day').
'lint' inserted within 'per' is 'plinter'.
'ss' going around 'plinter' is 'SPLINTERS'.
Can you help me to learn more?
(Other definitions for splinters that I've seen before include "first-aiders?" , "Chips" , "Sharp frogments of wood" .)