A difficult to understand context

The protagonist, Philip, got the appointment as assistant house-physician at St. Luke's.
He is going to be a doctor on a ship after finishing the appointment as assistant house-physician at St. Luke's.

For this was only a beginning. He had got into communication with the various companies which took surgeons out on their ships, and knew exactly what were their routes, and from men who had been on them what were the advantages and disadvantages of each line. He put aside the Orient and the P. & O. It was difficult to get a berth with them; and besides their passenger traffic allowed the medical officer little freedom; but there were other services which sent large tramps on leisurely expeditions to the East, stopping at all sorts of ports for various periods, from a day or two to a fortnight, so that you had plenty of time, and it was often possible to make a trip inland. The pay was poor and the food no more than adequate, so that there was not much demand for the posts, and a man with a London degree was pretty sure to get one if he applied. Since there were no passengers other than a casual man or so, shipping on business from some out-of-the-way port to another, the life on board was friendly and pleasant.
[Of Human Bondage by Somerset Maugham]
I'd like to know if "tramps" is the same as "a casual man or so, shipping on business."
Thank you in advance for your help.