The Hours of Work and Manning (Sea) Convention, 1936, is a set of rules about how many hours people can work and how many people need to be on a ship (called "manning" a ship).
It says that people who work on ships shouldn't work more than 8 hours a day or 48 hours a week. It also says that all work on ships should be spread out over 7 days and that people need to have at least 1 day off in every 7.
The convention also says that there needs to be enough people on a ship to make sure that it is run safely and that the people who are working don't get too tired from working too much.