George,
I'd bet all the money that I have in my pocket right now that your prop is over pitched. Too much pitch causes excessive torque load, and that's why your engine won't reach rated RPM. A proper pitch will let the engine spin up to max RPM when the boat is making hull speed. Too little pitch lets the engine rev, but all the reves won't get you to full speed. Go to the prop manufacturer's website and you will find a way to get a prop recommendation specific to your boat. For example http://www.gori-propeller.com/index.asp?ID=146 . You will be asked for information like the engine, engine HP, max RPM, reduction in the transmission, hull length, weight of the boat, etc. They will tell you the exact prop that is best for your boat. BTW, I know from my own experience that the prop recommended by each manufacturer will be specific to the performance of their prop, and will be a different diameter and pitch that what is recommended by another manufacturer. For my 38, with a 36 HP engine turning 3000 RPM, I had recommended diameters of 15 and 16 inches, in combination with pitch from 10 to 12 inches depending on the manufacturer. Rick Brass From: CnC-List [mailto:[email protected]] On Behalf Of George Cone Sent: Tuesday, January 14, 2014 4:03 PM To: [email protected] Subject: Stus-List folding prop for C&C 40 I am considering adding a folding prop for the boat and wanted to know if anyone had information on the recommended size of the propeller and what the size of the shaft might be. The boat is a 1981 with the 27 hp - yanmar 3HM- the engine is rated for 3200 rpm, but normally will only go to 2600rpm. Thanks George A Cone [email protected]
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