dont try travelling without the perfect bag - what remi mentioned. i use to put my wet suits to the nose and to the end of the board. that save my extra weight and little bit more durable.
check the airlines' official offers - huge differences!! choose that offer which give fix price per item or size, not weight price.
its just a roumor...!!! some of the airlines have fix price for different sport tools. in this case you can try EVERY nice ladies at the desk
and one of them wont know for sure what is the different between surf and windsurf. stay with her and check your gear in as a surf board. of course this is not an official solution and only the criminals try this way...
- as i said just a roumor... some years ago from st thomas to atlanta cost 70 bucks.