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 definition defines the answer.
'aboard ship decorator without a' is the wordplay.
'aboard' is an insertion indicator.
'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' indicates putting letters inside (some letters go outside or 'without' others).
'a' becomes 'per' (eg 'one a day' means 'one per day').
'lint' inserted inside 'per' is 'plinter'.
'ss' placed 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" .)