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Prop question

96motorhead

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I have an 89 eliminator tahoe 21ft open bow boat with the 330hp 454 and bravo 1 drive. We were out at the lake all last week and we did a few speed runs and I learned that the boat was running at 5300 rpm wot trim full up. Currently the boat has a 23p mirage 3 blade prop and it ran 65 mph consistently. The problem is when my dad bought the boat originally he said he tried a 3 blade 24p and 25p mirage prop and when he took corners sometimes the boat would cavitate really bad. My question is how can I utilize the extra 500-600ish rpm and gain a little bit more top speed but loose the cavitation in the corners? Would upgrading to a 4 blade prop solve this problem?
Thanks in advance
 

Ragged Edge

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How many hours are on the engine? Has 5300 always been max RPM? The reason I ask is a tired engine will struggle to run the RPM it used to when fresh, so if you have a lot of hours on your engine you may want to freshen it up before you start to change the set up.

Typically , depending on slip, a four blade prop of the same pitch will run less RPM than a three blade. As will higher pitch three blade props so it is unlikely you will run higher RPM going to what would be called a bigger prop. Running the numbers on your current prop, guessing a 1.5 to 1 ratio in your Bravo, your at 16% slip, not bad. As far as cavitation you may need to work with a good prop shop that can either recommend a prop or modify one to stop the issue.

I would suggest that you focus on getting your engine tuned up and running at it's best, then find a shop to work with and start trying different props. Some shops have a loaner program where you basically rent the prop until you find one you are happy with.

Good luck.
 

96motorhead

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Thanks for the help. I never knew this thread got a response and I forgot about it. I have no idea how many hours the boat has, my dad bought it new back in 1989. The boat sat for a good 15 years in the garage and was never ran which could be good or bad. If I had to take a guess though, it probably has 600hrs but that is a rough guess, and to be honest it was never abused during its life so I don't see it having any mechanical problems. I was basically just wondering if a simple prop change would allow me to pick up a few miles per hour if possible.
 
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