I didn’t mean to come across as an @$s but there’s a lot of bot posts lately registering and picking up a post from an old thread and posting.
All of that being said, a 21p Rev 4 would be a decent prop. If that boat won’t hit 60mph (53kts) WOT, a Bravo FS in a 21p would work as well, but as Grem stated, they’re made of glass. 1 meeting with mud or shell and they’re toast. You’ll lose 3-5kts off of 1 ding. If you want to go fast, Bravo is your ride. If you want to go decently shallow and almost as fast, a Rev 4 is the screw. If you want to be able to set it in your back yard on a rainy day and do donuts, call Jack Foreman. His 3 blade (with more cup than the yeti your drink your morning coffee from has) gets it done and they’re tough.
So went back and looked at the Props to make sure I had all the numbers right. I made a mistake and the current prop is a Merc Bravo I 4 Blade 20 Stainless and I'm getting 43-45knts on it. I'm going to try to find a Bravo FS 23.5 to see if I can test it out to compare it to the Bravo I. I did try out the Merc Tempest 3 Blade 26 because I had it, and your right it doesn't work well as it cavitates at the hole shot terribly.
