Gam is a nautical term to describe one whaling ship (or "whaler") paying a social visit to another at sea.
[1] The term was first used to describe a school of whales, and whalemen may have taken its meaning from that source.
After explaining that the word does not appear in dictionaries, he gives his own definition: He then expounds its meaning for whalers: William Hussey Macy describes the meeting of two ships at sea as a "beautiful and imposing sight".
He describes a "good old-fashioned 'gam'" as "rough entertainment," but with a "vein of politeness and deference to their guests... which might be studied with profit by many accostomed to more courtly circles."
Macy reported that "a man who should overstep certain bonds in his intercourse with visitors from a strange ship... would be taken to task unmercifully by his shipmates."