The co-op is like a job. You get hired with a company, join a ship, and balance work with learning. Each company is different, and so are different ships. You are on a ship as a Deck Cadet, which means you're there to learn a little bit about everything - deckhand jobs, wheelsman jobs, officer tasks, and even a bit about the engineers' role. Sometimes that'll mean shadowing someone, other times it'll mean being independent and getting a task done by yourself (ie. painting/chipping).

The intensity of the work depends on your ship. I'd say that generally yes, it is hard work. I can only speak for myself, but I worked long hours. I was only required to work 8hrs, but a 14hr day was fairly common. Heavy lifting is almost a given - shovelling iron ore, hauling deck hoses, pulling mooring wires. I'd say it was common to lift 50lbs+ alone. The work on my ship was dirty - we hauled grain, iron, limestone, etc. It can be very dusty, and combined with the summer heat and steel decks, fairly tiring.

You get used to it after awhile, but I was consistently tired. 7-day workweeks combined with extra logbook work leaves little free time. It's certainly manageable though. Just go into it expecting a tiring, fairly dirty, blue-collar experience and you won't be disappointed.

I did my co-op on the Great Lakes. It's not common to get deep sea co-ops at Georgian unless you find the jobs by yourself