Well, those numbers aren't precise for several reasons:
1. The ship's decks are curved upward at the ends
2. The ship's height depends on the weight of the cargo
Floor of crow's nest: 83 feet
Floor of the bridge: 61 feet (At the wheel)
Floor of C Deck: 34.5 feet (At the center of the forward well deck)
I think you mean "C Deck" as "Main Deck", it's the most obvious and recognizable deck, and also the lowest deck open to air.