Prop change needed for new Setback?

[classiccat]

I gave myself an early Christmas Present: A Humminbird Sidescan.

It requires clearance on both sides of the transducer forcing me to give the outboard some setback. I'm installing a 2-piece Jackplate (from T-H Marine) which will give me 4" of setback.

I'm currently using 0 setback and I have the outboard elevated to put the cav plate even with the keel.

2 questions for the experts:
1) Do I need to change the position of the cavitation plate relative to keel with the new setback (if so, approximately how much raise/drop do you recommend...and why?)
2) Is my current prop (10x13) OK to use with the new setback? (If not, what's recommended? 10x15?)

Boat: 16.5' BlueFin Seahawk (1983; converted from a side console to center console; http://www.youtube.com/watch?v=FCUYb5x7IXo)
Outboard: 83' Evinrude 35hp (2 stroke; I est the weight to be 120-130lb)
Prop: 10 x 13
Max Speed: ~25mph WOT (I apologize, I don't have a tach installed for Max RPM with my current setup)

...Or am I completely overcomplicating this considering the size/weight of my engine with this amount of setback?

 

[Bondo]

Re: Prop change needed for new Setback?

...Or am I completely overcomplicating this

Ayuh,... Run it, then see if Anything needs changin'.....

 

[steelespike]

Re: Prop change needed for new Setback?

Raise the motor to a point just before venting(cavitation) becomes a problem.