As pointed out, it depends on the marine vessel, the configuration of the loading dock, how your vehicle is loaded, and sometimes the type of vehicle your loading, and the order when loaded.
I can only confirm on the three ferry routes I been on, as on the M/V Taku in 1993 (Valdez to Seward) my memory is not 100% clear however I think we loaded from the side of the vessel as it took quite a while to load all the rigs....I can only remember while unloading after arriving at Seward that upon exiting it was out of the same access point that you entered, as my vehicle was one of the last one's loaded and one of the first unloaded....I do not know how the long RV's were unloaded however there is plenty of room to turn around once the compartment area starts emptying out to where it wouldn't be a nightmare maneuvering.
Sailing on the M/V Matanuska in 1994 (Skagway to Juneau and Juneau to Haines), I do remember loading from the side of the vessel, as I was thinking man that is a smaller loading dock they have here in Skagway, I was thinking what a cluster it is going to be when unloading in Juneau (Auke Bay) assuming the vessel was going to unload the same way as the M/V Taku the year prior....
June 1994 - Skagway Harbor - M/V Matanuska and loading dock ramp from land view (top picture):
When the M/V Matanuska docked in Auke Bay, it really surprised me that we all drove straight out of the ship so efficiently (forward in, forward out), and it was a breeze....there were two different access points to enter and exit the vessel.
Same ship sailing on the M/V Matanuska three days later (Juneau to Haines)...loading was fast (as the loading dock access was flat), unloaded at Haines the same way straight out of the ship (forward in, forward out) as there loading dock access in Haines was also flat that I remember.
Also noted about the large amount of staff members and spotters to guide you when loading your rig that run the Alaska Marine Vessels are top notch and really know what they're doing, they will take care of every passenger and rig onboard.