Darrenb:
Yes you are right. Just found the regs. You can have one hour interrupted rest but must have eleven off. Worked out ok for me as had over three off before getting on the boat.
I thought you meant you had 3 hours rest earlier in the shift but it now looks like you had over 3 hours rest while waiting for the ferry, if that’s the case and you used the ferry option when boarding the ferry you would have completed the regular daily rest period while on the ferry.
Either way you’re legal but if the 3 hours rest was immediately before boarding the ferry and you used the ferry option to board the ferry you could have continued the journey when disembarked if you wanted.