50 things on the Argo

OARS

Think of what Jason’s legendary ship needed in pairs to cut through the waves.

The Argo was the ship from Greek mythology used by Jason and the Argonauts, and "50" hints at the number of its rowers. Each rower used an "oar," so 50 rowers would mean 50 oars. The clue plays on the literal count of oars rather than something more abstract, making "OARS" the straightforward answer.