I got in trouble with Lufthansa. Leaving Australia was no drama, but getting back was different. Lufthansa refused to take the board. It was a 6.2 regular surf board - nothing big or heavy.
I had to pay them a hefty fee to get the board on the plane, can't quite remember exactly but around $100. It seems to be up to the airline and the local airport policy.
Pack it real well. When I finally got the board back on Australian soil the heavy duty board back was totally ripped and the tail of the board was completely smashed. Hundreds of dollars worth of damage after paying Lufthansa just to get it on the plane