The propeller that came with your new engine isn't necessarily the one that is best suited to your needs. This is because many original equipment props, understandably, are made to meet a range of average conditions for many kinds of boats, hull styles, and loads. This can limit their performance. What you need is a propeller specifically selected for your kind of boat, and your style of boating.
The size of a propeller is described using two sets of numbers. These correspond to the diameter and pitch. The pitch always follows the diameter when describing a propeller.
Diameter: Diameter is two times the distance from the center of the hub to the tip of the blade. It also can be looked at as the distance across the circle that the propeller would make when rotating. It is the first number listed when describing a propeller. The second number on the boat prop is the pitch of the propeller. The pitch determines the angle of the prop fin and how far the prop will move you during one revolution.