Flex-O-Fold Propeller

[DMorri3035]

I have a 1990 (#1093) C34 Mark 1.5 with a M35 30 hp.  I have been looking at several different folding props and really like the Flex-O-Fold 2 blade.  Just got a letter back from the factory and they suggested a 16x13R propeller.  Now I have a 15x10 Michigan Wheel 3 blade fixed and I believe I am over propped as I can only get 2200 rpm on the newly calibrated tach at 7 knots perfect conditions.  What size shaft did my boat come with and what is the forward ratio of the Hurth 100. 

Curt Morrison

[Noah]

Standard C-34 Shaft is 1 in.
Hurth 50 Trans: reduction is 2:1
I have smaller XP engine with 15 x 10, 3-blade Flex-o-fold
I have replaced bronze shaft with stainless steel shaft. I also have a Vetus Bullflex flexible coupler and standard stuffing box. All works well.

[David Sanner]

I'd be careful in going over 15" in diameter as you could get buffeting on the hull.

If you're over propped @ 15x10 ... 16x13 will surely be too much. 

Finally, what's your max RPM at WOT in neutral? 
It should be close to your max RPM motoring on a calm day in flat water (and without black smoke).  If it's not then you are likely over propped.

[Ron Hill]

Curt : Your M35 engine (30hp) came with a Hurth 100 transmission. 
You just might well be over propped if you have a Michigan Wheel which may not be a 3 bladed "Sailor" type 15" X 10" prop!!

As mentioned your shaft diameter is 1".  Also I would caution against a larger diameter prop from 15 inches.  Look in the Mainsheet tech notes and you'll find an article I wrote about Pops, Pitch and Boat Speed. 

A few thoughts

[DMorri3035]

My WOT is 3200 in neutral and 2200 in gear with my 15x10 Michigan Wheel.  Before I order my new prop I don't want to be over propped and feel my wide open throttle in gear should be 2800 to take advantage of the higher power band of the engine.

Thanks for the info -

Just wondering if anyone else out there has the 2 blade flex-o-fold with the M35 and Hurth 100 and what their WOT in gear is.

Curt

[David Sanner]

If you don't have any engine issues then it sure does sound like you're over propped.  Ron makes a good point about your prop may not be a sailor prop... and checking his article.  Good luck.   Sailboats like folding props ;)