OK, I have a fairly good grasp on how pitch, diameter and rpms affect speed/performance. (I think, anyway.) My Fisher 17' aluminum deep V is powered by a Mercury 90hp 2-stroke. (My motors max rpms should be right at 5500 based on the book.) The boat came with a 21 pitch 13" aluminum prop and the previous owner threw in a new 13.25" prop with 19 pitch. I noticed with the 21 pitch prop, the boat was sluggish on the low-end and I could never get the max rpm's above 5200. Top speed with that setup was right around 37-38 mph with 1/2 tank gas and a couple people and gear. Last fall I switched out the 21p for the 19p. Bottom end was greatly improved and top end was 35-36 mph. However, according to my tac I can hit nearly 5700 rpm at WOT. *Probably not good, so I always keep the rpms right at 5500 on the tac. So I'm thinking there is room for improvement, just not sure which way to go... If I stick with aluminum, I'm guessing a 20 pitch prop sounds like the ticket. However, it seems that they are rare birds and a little pricey. The other alternative is to switch to a stainless prop. What I'm not sure about is how much difference does a stainless vs. an aluminum prop make? I've heard that there is less resistance in the water with thinner stainless props. How does that affect overall pitch and rpm's? If I were to buy a stainless prop do I want to stick with something in the 19 pitch category, or possibly jump back up to a 21 pitch prop? Also, how big a difference top-end vs. holeshot on 3 blade vs. 4 blade on the stainless props? Questions...questions?