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Correct Prop Pitch

wickeral

Regular Contributor
"I have a 1997 Sea Ray Sundanc

"I have a 1997 Sea Ray Sundancer, 7.4/300HP. with a Bravo III drive. The boat came with 26 Inch pitch Props. Manual and local Mech. say to use 24 Inch. Prior owner was a serious cruiser who would take this boat on long distance trips. I figure he wanted better Fuel usage so he stepped up one available pitch. My RPM maxes out at 4100 which really is of no concern to me as I run at 3000 most of the time. Manual wants 4600 RPM but I'm uncomfortable running a Big Block that high for any length of time. Please tell me your thoughts! Thanks, Al W."
 
"Al:

I'm no prop geniou


"Al:

I'm no prop genious, but if the 26P limits the RPM to 4100 then isn't the engine working under a harder load? The 24P allows the engine to reach its optimum operation at 4600 RPM. Just my thoughts."
 
"Thanks Bert! Unfortunately th

"Thanks Bert! Unfortunately they do not list suggestion for Bravo III. (Only B-I). Anyway, Guy, I'm primarily a car mechanic. Therefore I equate Prop pitch with Differential Ratio. Seeing as I only run 3000 RPM why is top end RPM so important? Especially with a Big Block. Yes, the higher pitch does load the engine, but does it overload the engine?"
 
"Agree with Guy - "probabl

"Agree with Guy - "probably not". Most manuals state an rpm range, like 4000-4500 at WOT (wide open throttle) The boat should be propped to operate in the stated range under normal weight load (fuel, gear, people). That doesn't mean it should be run at that rpm all the time, it's just
a guide to make sure the engine is not overloaded
regardless of what speed it's run. If the prop
won't let it turn up those rpm's at WOT then it
will be overloaded an any speed. This applies to
any marine engine, the number of props has no bearing on selecting the right pitch."
 
"I feel vindicated! As we all

"I feel vindicated! As we all know, an engines rotating assemblies sustain maximum load/stress during hard acceleration. This also applies to the Gearing/Bearings etc. in the outdrive. With this in mind, while getting up on plain is the most stressful portion of any cruise. Our boat does this with ease so I'm comfortable with the current Propping. Thanks to all! Al W."
 
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