C&C 27 Association – Props
The following is information submitted to the Forum on prop choices. Negative opinions have been provided along with positive ones to give a sense of the range of possibilities. If you have a match that isn't covered (or that is, and you'd like to reinforce comments here), please let us . All props are 2-blade, right-handed unless otherwise noted. For pictures of a variety of props, see here.
Most shafts are 7/8" but there are reportedly some 1" out there. The taper is probably SAE (aka, 'Standard'), but you should ask a prop shop to check. These boats are old enough that a previous owner may have slipped something different in there.
Mark I & II
Boat Name Engine Prop Comments Hyperion Yanmar 2GM20 Max-Prop 13" x 13" (28 deg) "I usually run the Yanmar at 2800 RPM as this is where it seems most comfortable and the boat will go all day into the wind and swell at 5 1/2 knots." - Ralph Ainslie Penny Whistle Yanmar 2GM 13 HP 11x9, 3-blade "I can rarely achieve more than 4 to 4.5 knots. This seems slow." - Carl Armstrong
Mark III & IV
Boat Name Engine Prop Comments Kat's Paw I Atomic 4 Gori 2-blade folding, dia & pitch n/a Fine in forward but no reverse thrust, lots of prop walk. Owner and others (skilled boat-handlers) hate it. Iris Atomic 4 Martec folding 11x5 "This came with the boat and delivers plenty of drive. The 5-inch pitch allows the engine to turn over at a comfortable rpm when cruising at 5 1/2 knots. - David Masury Rhapsody Atomic 4 Michigan Blue Dot folding 12x5 "The builder's file shows that there was a 12x5 folding prop instead of the standard when built. I always thought that this prop was a bit large, as the A4 seemed to lug, unable to come up to decent RPMs (no tachometer, but I've spent a lot of time around old gas engines)." - Bob Wooden Santiva Atomic 4 Indigo 10x7.4 3-blade "Prop-walk from the original fixed two-blader led me to the fixed three-blader from Indigo, designed specifically for Atomic 4's. Prop-walk now is negligible, reversing brings the boat quickly to a stop and while a folding prop would have yielded a fraction more speed (at significantly higher cost) I'm a cruiser." - Ken Pole Towser Atomic 4 Flex-o-fold folding 12x7 "Great prop with lots of thrust in forward or reverse." - David Weatherston Yanmar 2YM15 Flex-o-fold folding 14x12
Mark V
Boat Name Engine Prop Comments August Westerbeke 12B 2 diesel through a 2.05:1 reduction. 12"x7" fixed 2-blade "Can't make hull speed in still water at 3000 rpm (rated maximum)." - Lou Potente Distant Thunder Yanmar 1GM10 Flex-o-fold folding 13 x 10 RH "Works great in both directions." - Jim Wente Dragonfly Yanmar 1GM10 with 2.62:1 gearbox Gori 13x9 RH (original fixed-blade was 12x9) "It seems about right. Will rev to 3600 giving boat speed about 5.5 knots or so. Would continue to accelerate if I let it (which I don't!). Am told not all these boats may have same gear ratio, and that matters a lot with prop selection." - Rod Millar Heatwave Yanmar 1GM10 Gori 13x8 "The engine cannot achieve 3600 RPM in gear, so I think this prop is too big, or else the boat is overloaded with gear." - Bob England Underdog Yanmar 1GM10, 8 HP Gori 14x9 "Seems a little big but it only cost $100 so I went with it. The boat will only do about 5 knots at about 2500 - 3000 rpm. The old fixed prop was better at 12RH9 for speed which pushed the boat along at about 5.5 knots." - Cameron Paine (Later, he reported that a new cutless bearing added 3/4 knot to boatspeed.)
