I live directly on salt water and take my cameras out in my boat often. I keep the camera in its bag unless I am using it when on the boat. I do take pictures moving at high speeds but not when wave action could cause spray – the boat is usually dry. I think if you stayed on the front of the ferry or similar boat you wouldn’t be subjected to spray unless the seas were particularly rough.
Mist doesn’t have salt in it, just spray. If “sea air” had salt I would probably have lost a lot of equipment by now.