Fixed blade prop specs vs folding blade specs

[BigEasy]

For those of you who have converted from a fixed blade prop to a folding prop (or those who have knowledge about props), did you select the same size diameter & pitch or did you resize? Initially, I thought that it would be the same; however, with folding prop blades having a different shape & surface area, maybe a slight difference in specs would be in order. Do any of you have knowledge of an online calculator for sizing a folding prop?

 

[Davidasailor26]

We went from a 3 blade 17x12 traditional style fixed prop to a 16x12 Flexofold. The Flexofold size was based on the manufacturer’s recommendation after I provided them engine and transmission specs. The Flexofold is at least as fast under power, maybe a touch faster, and both props could reach the engine’s spec’d max 3600 RPMs in forward.

 

[Rich Stidger]

I converted from a 2-blade standard prop - I think it was 18 x 16 - to a 3 blade feathering AutoStream. The manufacturer set the pitch based upon my engine, transmission, and boat. The feathering prop is 18" dia and I think the forward pitch is about 12".
I saw better punch-thru in forward, huge braking performance in reverse, and 1/4 to 1/2 kt gain in feathered position.
The recommended pitch settings for fwd and rev were right on.

 

[dlochner]

The manufacturer will provide the specs or a good naval engineer. The prop manufacturer won’t charge for the information.

 

[BigEasy]

Thanks, waiting on specs & estimates from flexofold & Gori. I already have a Volvo folding prop that has corroded blades; can't get any info from them about replacement blade specs & they will not allow me to forward my boat's data to their technical department. Have to deal directly with their dealers who may know nothing about folding props for sailboats. Crappy customer service IMHO.

 

[danm1]

Got a new flexofold this season per the manufacturer's recommendation. They didn't even ask what the about the size of the old prop. The new flexofold gives me another knot + of boat speed at 3600 max rpm, and cruises more reliably at 6+ knots at about 2800 rpm. Also eliminated major prop walk from old fixed prop.

 

[jssailem]

Big Easy, you should work with the prop shop to get the correct size on your boat, engine and transmission.
The diameter and pitch are based on the space available from the shaft to the bottom of your boat. Too close to the boat bottom and you develop turbulence that reduces your performance. Pitch influences the rpm performance of your engine/transmission.

 

[BigEasy]

Big Easy, you should work with the prop shop to get the correct size on your boat, engine and transmission.

Received specs & price estimates from Gori & Flexofold yesterday....exellent customer service. As you all know, quite expensive. I am still inclined to keep my present Volvo folding prop and replace the set of three blades and blade shafts...much less expense than replacing with an entirely new prop. Plan is to wait until October, until I haul out, when I can remove the blades and visualize the part number for the correct blade set. My suspicion is that it is a 17' x 11" (same as fixed prop from factory), already know it is RH with 25mm bore.