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big_nasty1

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What is the best way to determ

What is the best way to determine the correct prop size for a boat. I think I am a little under-proped. I'm running a 1979 34 ft. Marine Trader with a 120 Lehman. I have been running @ 1750 rpms while only cruising at 5.6 kts. The prop is a 4 blade 24 X 16. Paragon transmission with a 2:1 ratio. I need another knot! Thanks
 
"Can you run the boat up to ma

"Can you run the boat up to max RPM? The correct prop will allow you to turn @ 2500. If you can turn the engine faster then you need more pitch in the prop, can't get to that speed you need less pitch.

Finding the max R's available will start you to the solution. Then go to Michigan Propeller site and fill out the worksheet and it will give you an approximate wheel size and pitch. A lot depends on how your boat is loaded and used.

Another owner with the same type boat, loaded the same as yours, and used the same as yours could get you close too.

Another thing to think about is that every prop is just a little different. The absolute best way that I've found to insure I have the prop on the boat that works best is by computer tuning the prop. That way you know all the blades are in perfect alignment, all are flat as measured in 3 or 4 spots out from the hub, and you can have another prop made exactly like the first if you damage it. The measurements are kept on file and you'll get a copy. Or heaven forbid you can straighten your prop if it gets tweaked.

K"
 
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