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Difference in handling that prop diameter makes, especially with a Sportmaster case

Guest Contributor

Hello, just looking for advice or guidance on how much prop diameter affects handling when running elevated engine heights. I am going from a Bravo XS to a Promax and of course I will adjust my engine height as needed based on how my boat handles....I have ran both Bravo's and Promax's with my previous 250xs but that was "below pad". For reference, I'm trying to set up a Bullet 21xdc with a 300xs and 1.75 Sportmaster. Currently my 30 Bravo XS is sitting at 1" above pad and is just below limiter (6400) at 86.....its roughly 18% slip, which theoretically going to the smaller diameter Promax, would get worse in my mind if the engine height was left at 1" above pad. If slip gets worse, handling should or would be worse as well I presume? 


Official Racing Partner

There are a lot of different things to think about in this situation.   1st is the barrel size.   The bravo has a full barrel where as the Pro-Max has a smaller barrel.   The larger barrel will help with overall lift from the motor as it extends the gearcase thus creating a "larger waterski" per say.   Second the Pro-Max has what is called a parabolic Rake to it so its progressive.   This will help your slip Vs. The Bravo XS.    You didn't say anything about going up, down or staying the same pitch wise but i'm guessing you might be able to go up a pitch with the Pro-Max.   Are you using the same set back?  

Brett Seubert

Team Racing

Hi Bullet21, just like Brett said there are many factors when switching from a Bravo XS to a Pro Max. Bravos also run lighter in pitch, which makes the slip calculation come out high, 15-16% is pretty normal and I wouldn't consider 18% as too high. The bigger barrel on a Bravo I propeller lifts the stern of the boat more, I like to think of it as effectively raising your engine height when running compared to a Pro Max or solid hub props. Pro Max are usually good to about 1.5" above on setups like yours, which is a great place to be with a 300XS. Remember to make sure your cav plate on the gear case is perfectly level/ zero degrees with the pad of the boat before measuring, the new cell phone apps work great if you don't have a digital level. 

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