What you put on the boat
The car runs out before the cabin does.
I have watched people plan a berth and a bottle of wine, then discover the vehicle deck is full. Book the car, the truck, the trailer, before you decorate the trip.
A spot for the vehicle
Passenger tickets and a vehicle reservation are not the same kindness. In summer, and any week a holiday leans on Newfoundland, the deck fills. If you are driving on at North Sydney, that line on the booking is the one I would not leave until tomorrow. Trailers and anything tall need you to be honest about length. The crew is not guessing for fun. A wrong length is how a calm morning becomes a conversation in the lane.
Cabins and chairs
Cabins come in a few sizes: a bunk you can lie flat in, sometimes with its own head, sometimes shared facilities down the corridor. I do not memorize the brochure. I ask whether I can shut a door and whether there is a bunk for each person who cannot sleep sitting up. Seats are perfectly respectable on the seven-hour crossing when the weather is boring, which is the weather you want.
On the sixteen-hour Argentia crossing, a cabin is the difference between arriving able to drive and arriving as a folded coat. If the cabin you wanted is gone, a seat still gets you there. Pretending you will “nap in the lounge” for sixteen hours is how my brother once arrived unable to find the car keys that were in his hand.
Pets
Dogs and cats can come, and they do not sit in the cafeteria with a menu. There is a kennel routine: you visit, you do not move in. Tell the truth about the animal when you reserve. A surprise dog at the check-in window helps nobody, least of all the dog.