On the many times I used a ferry with the old Triumph Rocket this is what I did....
While waiting to board get all the straps etc ready - I carried them all in a spare plastic Carrier bag (Iceland freezer sack is great
)tied onto the luggage rack with it's own bungee strap.
On the ferry park up on the side stand, leave it in 1st gear.
Use my disc lock reminder which was a cut down bit of bungee strap - this goes round the front brake handle so that the elastic holds on the front brake (this stops you riding off with the front disc lock still on).
I then used my own straps to tie down the bike (available from B & Q) - I connected one end to the right side of the bike over the seat and secured it to the ferry on the left - the other went from the bike left side to the ferry on the right side. These can be adjusted so that the bike is well secure and won't tipple over.
You normally get quite a bit of time to tie down but when the time comes to leave it's a made dash. It'sworks out great if all you have to do is stuff everything in a plastic bag and tie it to the bike. I don't even have to stop on the dock and re-adjust anything.
As I said this routine worked for me with the very heavy Rocket, never had a problem at all.
One tip though..... Have a practice in your garage before having to do it on the ferry. Sounds daft but it will help.
Doc