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What is the correct Prop Pitch for my boat?


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I have spun two hubs now in my prop. (Boat: 2000 Chaparral 245SSi Merc 5.7 EFI Bravo 1)

Went to the prop shop again today, they advised me that I had the incorrect prop/pitch on it and that is why I keep spinning the hubs.

The prop that was on it when I purchased the boat (two months ago) is/was a Turbo three blade stainless 22 pitch.

The prop shop told me based on their book, I should be running at WOT 4800-5000 RPM. With the 22 pitch I am only running 3400.

I now have a new 17 pitch four blade aluminum prop (Diameter 14.5) that they recommended (have not installed to test yet).

What is everyone thoughts? Suggestion on the pitch/number of blades?

Thanks!

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Unless someone has fooled around with the gear ratio on the Bravo 1, it should be a 1.50 gear ratio. A 17" pitch with a 1.50 gear ratio makes a lot of sense to me for that particular hull and powertrain. Given your current prop pitch and RPM, I'm inclined to believe you have the 1.50 gear ratio.

As the 245 SSi was really a rebadged 2335 SS, you could expand the search to see what others on the forum or net might be running for props with a MerCruiser 5.7 EFI. Personally find 4 blade ss or aluminum to give the best all around performance on a single prop boat. The 245 SSi of course was only made for a few years.

The only real concern I have is how an aluminum prop (even if it is a newer style Spitfire or Nemesis 4 blade aluminum) will perform on your boat due to it's weight and power. If the boat was mine, I'd look at installing a 4 blade ss prop such as the Revolution 4 in a 17" pitch right hand rotation, but the engine has to be able to turn it. IMHO, you'll want closer to 4800 RPM than 4400 RPM at wide open throttle with an average load. At the very least, you'll need to test the 17" prop to see how the boat performs.

NOTE: should you ever smash the lower unit off a shoal, and really want to improve the boat up regarding all around performance, than I would install a 2005 and newer style Bravo 3 drive in a 2.20 gear ratio, and install 24" props. The 2005 and later Bravo drives shift a lot smoother and quieter than the older models.

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Unless someone has fooled around with the gear ratio on the Bravo 1, it should be a 1.50 gear ratio. A 17" pitch with a 1.50 gear ratio makes a lot of sense to me for that particular hull and powertrain. Given your current prop pitch and RPM, I'm inclined to believe you have the 1.50 gear ratio.

NOTE: should you ever smash the lower unit off a shoal, and really want to improve the boat up regarding all around performance, than I would install a 2005 and newer style Bravo 3 drive in a 2.20 gear ratio, and install 24" props. The 2005 and later Bravo drives shift a lot smoother and quieter than the older models.

Shep, I know my Bravo 1 has a 1.33 gear ratio and if he does, it makes even more sense why he's running such low rpms.

Also, will that Bravo 3 lower unit bolt right up to the upper unit? That's what I'm kinda hearing but since the shifting is in the upper drive, maybe I'm misreading?

Thanks.

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Finally installed the new prop and test drove. WOW what a difference. It's a different boat now. Acceleration is incredible and get moving much better with the 17 pitch prop.

I did notice that at WOT I was running 4200-4300 rpm, too low? Wonder what my gear ratio is with that being said.

Thanks again everyone!

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