In the Royal Navy he is called an Oppo, short for opposite because he would be on the opposite watch and they would hand over duties to each other and take care of each other too.
Seaman.
Crew
Sailors on any type of vessel are called a crew of sailors.
A collection of sailors is called a crew of sailors.
A duck's mate is called a drake. The duck is female, the drake, male.
This is called mutiny and the sailors are mutineers.
sailors
Mariners
Chart.
A stallion's mate is typically called a mare.
British sailors were issued lime juice as a remedy for scurvy.
The name of the sailors that sweep the main deck are called "maties".