You might be better off just waiting until you get to the dock in PdC and booking passage on whatever ferry is next. With flight delays, uncertainty in ground transportation timing, etc. it may be challenging to determine exactly when you will get there.
And I'm not sure how many cruises are going on, but sometimes the evening ferries can be completely booked up by cruise lines for their passengers. I have to wait over an hour waiting as I already had a return ticket.