Post by jimesh on Oct 13, 2013 8:44:42 GMT -5
My #295, 1975 P35 came with its original A4 and 13X7 - 2 blade prop with direct drive (1:1). The A4 could not reach full rpm w/ this prop, and backing up involved a lot of prop walk, so I changed to the Indigo Electronics 3 blade 10x7.4 prop. This has not been entirely successful for several reasons: (1) The small prop size seems to be *much more affected* by fouling than the larger one was. Barnacles build up on the hub and inner areas of the blades especially (pretty much the same as on any other prop) but (I theorize) the smaller prop diameter means a more disturbed flow on the working surface of the blades from this level of fouling and a severe drop off in thrust by mid-season. (I anti-foul the entire prop every spring w/ 2-3 coats of a Petit 70% Cu anti-fouling paint.) (2) The small diameter of the prop probably means that flow to the working surface of the blades is more disturbed by the deadwood (aft surface) of the keel and the leading edge of the rudder than for the 13". The new prop does not seem able to match the net thrust of the old one -- top speed in calm water is a bit lower at about the same rpm. (3) Prop walk in reverse seems, if anything, to be worse, not better than with the 13" prop.
Overall I've come to the conclusion that the Indigo prop is probably not a good choice for the P35 due to the prop aperature of the boat and the small diameter of the prop. A similar conclusion would apply to other 3blade 10" props I've read about such as one from Michigan Prop. I'd welcome any thoughts or experience from others on these problems.
I'm considering switching to the CDI/PerformancePropellers 12x7 semi-flexible urethane prop that they advertise for the A4. The larger diameter (and flexibility that they claim) should help with at least problems #1 and 2 above and they claim to be better on #3 as well. Anyone have any experience with this prop on a P35 or other recommendations for the A4 in a P35?
BTW, CDI mentions that some C&C's have had their deadwood tapered to a finer edge near the prop but cautions about trying that on a boat w/ metal in the aft edge of the deadwood. Anyone know if the P35 has metal there, or has tried tapering that area for better prop performance? Of course the rudder shaft will always present a greater problem for a smaller diameter prop in reverse and there's no chance of making any change there.
Overall I've come to the conclusion that the Indigo prop is probably not a good choice for the P35 due to the prop aperature of the boat and the small diameter of the prop. A similar conclusion would apply to other 3blade 10" props I've read about such as one from Michigan Prop. I'd welcome any thoughts or experience from others on these problems.
I'm considering switching to the CDI/PerformancePropellers 12x7 semi-flexible urethane prop that they advertise for the A4. The larger diameter (and flexibility that they claim) should help with at least problems #1 and 2 above and they claim to be better on #3 as well. Anyone have any experience with this prop on a P35 or other recommendations for the A4 in a P35?
BTW, CDI mentions that some C&C's have had their deadwood tapered to a finer edge near the prop but cautions about trying that on a boat w/ metal in the aft edge of the deadwood. Anyone know if the P35 has metal there, or has tried tapering that area for better prop performance? Of course the rudder shaft will always present a greater problem for a smaller diameter prop in reverse and there's no chance of making any change there.