You can walk on the ship deck, you have to talk to Bosun to get there. But all doors are locked.
Actually you can get inside the ship by sneaking in through cannon door. One of front starboard side doors worked for me, just crouch and back in.
Gun deck looks great, I wonder why devs didn’t made it normally accessible. There is stairwell up to front halfdeck compartment. It looks a bit empty as entire ship, some crates, buckets and decorations should be added yet.
Orlop deck is fine too. Just that whoever was assigned to bilge pump, left long ago
I couldn’t get in storage hold, it’s submerged and player can’t dive. I’ve got there when wave got exceptionally low, but almost immediately got stuck crushed in the ceiling because game physics can’t deal with submerged player.
You can get out of there through horizontal door by fiddling on stairs under that.
I haven’t found way to sneak in officers cabins yet.
I’ve read that devs struggle with making hole to the water level that spreads over entire map under terrain included. I wonder if they could make the ship raise above water when player gets downstairs. Player could not see outside anyway, it could work as temporary workaround.