Oh boy, thats going to hurt, but if you stick with Hill marine not that much
Look at it like this.
B1 is 1.5 ratio, with lets say 19 pitch prop, turning 5000 RPM and getting 50 MPH. This equates to a prop slip of 16.6%
B3 is 2.0 ratio, turning same 5000 RPM, and 50 MPH, and slip is the same...