How exactly is the prop sizing determined? I have a good idea on the prop pitch and prop rake but not real sure how diameter is selected? We are running 17x38-18's on our 43ZR with triple 700's. What would going to 17.25 or down to 16.75 do? Don't have solid numbers right now as we just had the engines rebuilt and dynoed just shy of 750hp each but before rebuilds it would bounce rev limiters around 118-120mph with light fuel/ 1-2 people.

First, baseline numbers will be a must. Baseline numbers with something will get us to where we need to be.

Sizing is determined by the boats personality and by experienced propeller and set up professionals.
Your "X" dimension and baseline numbers will help me to get you to where you need to be as well as the questions I will ask you about performance including seat of the pants observations.
In short to your answer, decreasing diameter on ZR's can be a issue unless the depth of the X is increased. Your app. needs in depth discussion. I would love to talk about it with you if you desire.
Call me anytime.

Brett

Brett