B2 drives are best for large heavy twin engine boats that won't fully plane and will not exceed 30 mph WOT. With a 20 inch diameter aluminum prop it moves a lot of water and you don't have to worry much about galvanic corrosion. Backing is a issue with crabbing
B3 drives are best for mid range to large heavy single and twin engine boats that will fully plane and exceed 30 mph. The twin stainless props are good for efficiency and backing, they back in mostly a straight line. The bad is galvanic corrosion needs to be closely monitored
