Flexofold propellor

[sailnut]

I just got a quote from Flexofold and they suggest a 17" two blade for my 1991 with a 35b engine does that sound right?

[Ron Hill]

sail : NO The diameter of a prop is set by the boat manufacturer.  That diameter on a Catalina 34 is 15" so there is no buffeting from the prop blade against the hull.  I had a discussion with Gerry Douglas on the prop diameter and that's why he set it at 15 inches

There have been numerous articles written on this very question!!  I'd stick with a 15inch diameter, but again it's your boat. So don't be surprised with buffeting on the hull if you install a prop that's larger than 15" !!  

My thought

[Clay Greene]

I think something went askew in your communications with Flexofold.  Here is what Dan Tucker, former Flexofold sales manager in the U.S., recommended for the C34 (both the M25XP and the M35):

Those two engines are 23 HP and 30 HP respectively.  The reduction ratios are also different, resulting in a bit of difference in shaft/prop RPM. On the M35 I would recommend a 15 x 11 2-blade or a 15 x 10 3-blade. Flexofold sizing is generally +1" in pitch compared to a fixed prop, as our blade shape is more sophisticated and manufacturing tolerances are tighter. It's standard practice for us to subtract 1" of pitch moving from 2-blades to 3, in order to compensate for the increase in blade surface area and resulting change in efficiency.

I can forward the whole e-mail string to you if that would be helpful.  Send me an e-mail at greenesail@sbcglobal.net if you are interested.

FYI, last weekend I put a Flexofold 17x11 three-blade prop on our C387, which has a 40 HP Yanmar engine.  A 17 inch prop diameter is way too big for a C34, IMHO.   

[Stu Jackson]

Yes, maximum 15" diameter.  For ANY prop for our boats.