Ferry Mode

Old John:

barrykam:
You can’t use ferry mode on such a short crossing. I can’t remember the exact minimum length of crossing but 6 hours rings a bell.

Ok, I’ve not seen that quoted anywhere though. That would surely disqualify some of the channel crossings?

It clearly states that you must have access to a bunk or couchette. You don’t get a bunk or couchette on any of the channel crossings so you cannot use ferry mode on any of the channel crossings.
I take a ferry (I’m on one as I type this) at least twice a week. You crossing was not long enough for your Tacho to accept it as a ferry crossing.