We obviously have different ideas about the meaning of the word "abandoned". To my mind it is to leave, especially unattended, to give up on, or to withdraw support. The boat would have to empty to abandon it so cast adrift would be more appropriate. As for knitting, when you cast of you have finished the article, unless of course you do not intend using whatever has been made! As for paper, that is a bit obscure.
cheshunt, I apologise that my earlier definition was of cast off rather than what it should have been - cast-off. I appreciate there is a difference but this clue does say 4-3, rather than 4,3, and if it is read as cast-off it does mean abandoned as per the clue.
This is from the Oxford English Dictionary:
cast-off Brit > adjective no longer wanted; ABANDONED or discarded: 'a pile of cast-off clothes' (capitals mine).