Set back vs shaft length

[boat addict]

Hello to all this is my first post on here. Looking for some knowledge on the advantages of a 20" shaft motor on a 12" jack plate vs just running a 25" shaft on the transom. I have a 1987 21' Olympia, currently the boat has a 175hp fast strike Johnson that is on a 6"CMC manual bracket. I can tell that the motor is a little to high
or not far enough back. Depending on how you look at it. The boat on gps will do 52mph, which I think is pretty good for an ole tired Johnson. I would like to eventually put a 300xs on the boat. But don't know if I should go with a 25" shaft or a 20" shaft on a 12" set back. Other than being able to run in shallower water what are the advantages going the 20" route? Thanks for any input.

[JPEROG]

The lower you can get the weight the better off you will be. When boats start to run above 70 mph CG becomes an important part of the equation.

Joe

[boat addict]

Thanks. I didn't even think about the CG aspect of it. Am I wrong thinking that the longer shaft would have more leverage to carry the bow better? This is my first outboard, I've got more experience with BBC sport boats.

[olboatman]

Welcome to S&F and be prepared for some great "schoolin"! I learn something on here every day. I agree with Joe completely and a beleiver in shorter mids with setback. Gary