I'm flying from the UK with a sail in my hold luggage. One of the battens is too big and won't fit. Can I carry it on as hand luggage or would it not be allowed through security?
Be on the safe side.
Buy a cardboard tube and pack your sail baton with bubble wrap; leave one side easily accessible if security wants to look at it (keep some tapes with you if wanting to secure it if needed).
Mark it with your name/address... put on a "fragile" sticker on it.
When doing your check-in at the counter, ask if you can bring it with you, if yes, then YEAH!, if not, then just check in the prepared tube.
This is a case where you won't know until you try. Technically, the batten is not a prohibited item and meets the liner requirements of most airline rules but it is still an odd shape.
You should be able to stow it like a cane.
They're pretty sturdy, but I would at least wrap it in something.