the ferry guys should do the tie down for you but i did have them trying to do it wrong once cus they had the straps going straight across my nice shiny pannier paint and trying to give em a bollocking when they could speak a word of english wasnt easy so i gave up, took the straps off and did it myself ( i have recovering cars and bikes for 13 yrs and never lost one yet) put it on the sidestand if they dont have front wheel chocs on the boat , you dont need to remove the front wings at all, you can take you strap and thread over the top of the front mudguard (around the shocker) then bring the strap back on itself , then make sure when you anchor down there is a forward and side pull on those straps ( this will make it stable against side and reawards rolling ove the boat) then you can do the over the seat method if you like with a third strap or alternative to that it go from the pillion handles but be carefull about the panniers paintwork, whter going over the seat or the handles make sure you give rewards and sidways pull on these straps and by doing so the bike will be rock solid from any direction ( front, back, left and right rolling of the boat), trust me 13 years taking bikes tied down has proven to me the best methods, but while we are on this subject i must mention the amount of times i have seen people using a strap with a loop on one end and hooking that straight over the handlebar grips ( never ever do this unless you have the type of bike where you can then cross the left and right right strap over each other) if you cant cross them over then prepare for the consequencies when things get rough and the front suspension dips a little on the bike with the straps simply falling off the bars and your pride and joy taking a dive