Read this from Greg at VooDoo Props --- maybe it will help u understnad them better

97.74.115.176/voodooprop2/Tech/Polish.aspx

it's a how to for props

I like Brian's enthusiasm! If you're new to this, you dont need to spend a lot to get going faster - I'd make the recommendations Marc made happen immediately, and start with a sharpeneed & balanced 265 or 270 prop like Randy said. Marc gave you a good starting point for strut depth, you can always go up or down from there. That header change will make a world of difference, you will see with those things done (with or without an expensive prop) it will be MUCH faster. I tend to be a little cautious - thus the 1/16" increments (especially not knowing where you were set to begin with, or the condition of the motor internally). When tweaking, 1/16 inch can be a huge adjustment!

I should have told you a few things about myself. I started out as a play boater with an F-41 Stryker some years back. I kept tweeking and making changes and the boat got faster every week. I was being sucked into the speed thing and r/c boating hobby more than I could see. I started running my Stryker with other boaters to see just how fast my boat was. I joined the local r/c club and started racing. Racing is brutal and some of these guys are fanatics! Your constantly spending money on this or that in the quest for speed.
You don't have to go broke to make your boat fast. Just remember that there is someone out there that has the same boat that is twice as fast that has spent a ton of cash to get it there.
If you are just a play boater that does not race, you can save a lot of money! If you go the other way, prepare to open the wallet! Good luck, Brian