I work for a builders merchant and have to do deliveries to Scottish Islands. Twice a week I leave the yard at 4am and travel 2 hours to the ferry terminal then 2 hours on the ferry, i do deliveries for the next 5 hours in cluding the breaks, then 2 hours on the ferry back to the mainland then 2 hours travel back to the yard all in all 15 hours duty time, the days im not on the islands im in at 7.30am to 5.00pm, as things stand my working week would finish on the island on thursday morning, ive spoke to my boss about the WTD but he doesnt think its going to effect me or the other drivers who do the island runs. 
Only just noticed this one.
The guidelines specifically state that time spent on a ferry can be counted as a Period of Availability, although, logically, most people would count it as a Break. I presume that they have allowed it as a POA in respect of short trips such as the Torbay Ferry, or the Fowey Ferry. An artic on the Fowey Ferry 
Now that would be interesting.
If the time spent on the Ferry is not less than two hours each way, then you could count it as a Rest Period and do a 16 hour day, every day.