You wheel it on (cycle in the old days), park up using rope they provide and leave it. A couple of bungees might be helpful
Depending on layout etc.
Nb i see you have carbon fibre- yes, there is a good chance of other bikes being next to yours and leaning against it- your panniers will usually protect but something to consider.
Returning to this, as three of us are now booked Harwich to the Hook and back around the beginning of August.
Firstly, why would you leave your panniers on the bike? Isn't this an open invitation to steal the contents?
Secondly any additional padding you take will then need to be carried with you on tour, unless you bin it and buy fresh before you travel back.
Having never travelled on a cross-Channel ferry with a bike before I am a bit nervous about getting my new bike scratched and generally having bits like lights damaged. A lot of peripherals are vulnerable to abuse.
I assume that everyone locks the wheels to the bike frame. A dynamo front wheel might be a temptation to someone, not necessarily travelling as a cyclist.
Likewise a leather saddle is generally rated as very nickable. Do people leave their saddles on or take them off for the duration of the trip?
We are travelling on Monday nights so we shouldn't (hopefully) hit the weekend rush.
I'm generally looking for things that look obvious in hindsight. Things that afterwards people will say "Why did you do that? We always...".
Specifically what, if anything, is taken as an extra for use during the ferry trip and what is done to keep the bike safe.