2-bladed prop?

[zoidberg]

There's some speculation that one or two entrants in the GoGoRace have fitted 2-bladed props, which can be aligned with the rear of the keel, within the prop cutout. That's likely to give a drag advantage over similar hulls with 3-bladed props. On the basis that hull speed is considered to be around 1.2 X Root waterline length, suggesting hull speed on the 36' OA boats is a bit over 6.5 knots, how much might one gain by having a 2-blade prop 'aligned'....

.... or put another way, how much speed/time/distance will the 3-bladers lose?


Edit:

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[pmagowan]

I have heard a general rule of thumb that you ge t a 1knot average advantage from having a folding prop so maybe this compairs. Too many variables to give anything other than a rule of thumb answer I suspect

 

[sailorman]

look at the racing handicap Nos, that will tell you

 

[A1Sailor]

The Clyde Yacht Clubs Association has different allowances for 2-bladed vs 3-bladed props and also takes into account "apertures" and location - close to keel or not.

Variation - Allowance (min/hr) - Qualification

Folding Propeller - including feathering propeller (regarded as the Standard Configuration other than for yachts with keel apertures)
Fixed Two Blade propeller +0.25 where the propeller is exposed and not located close to the keel or in a keel aperture
Fixed Three Blade propeller +0.50 as above
Three Bladed propeller +0.25 where the propeller is close to the keel or in a keel aperture and cannot feather or fold
http://www.cyca-online.org.uk/cm/dynamic/Large/16052011114350.pdf

Edit:
I think the boat in zoidberg's pic would get the same handicap as one with a folding or feathering prop.

 

[Porthandbuoy]

The jubilee clips on my shaft have the screws aligned to tell me when the 2-bladed prop is aligned vertically within the aperture.

Any faster? Not that I can tell, but I reckon it's less likely to foul weed or rope.