Big thanks to Cranberry for an excellent puzzle - it was quite difficult but it's one of those that really rewards perseverance.
A couple of queries:-
One might send you off course forgetting bags (3)
I have the answer and the extra letter and get the definition but just can't see how that and the extra letter come from "course forgetting bags"
Rough measure of herrings caught by ship (5)
I parsed this as 4 letter "measure of herrings" (minus extra letter) next to/"by" usual 2 letter "ship" but can't understand what part "caught" plays?