Mercury - Complete Gearcase Bravo Three / Three X / Three XR Series Corrosion-Resistant Alloy 8M0046738. Overview. Anyone who's run a Bravo Three drive long enough knows the lower unit carries the weight of every good day on the water. When it's strong, smooth, and dependable, you feel it instantly-your boat lifts with purpose, tracks clean through chop, and settles into a rhythm that just feels right. That kind of confidence is priceless, especially when you're miles from the ramp with a full c