Sounds like the early mirage prop, pretty sure the mirage plus all had vent holes. The vent holes really help smaller engines getting on plane by allowing them to slip at low rpm's, but once on plane the water moves fast enough to render the vent holes inoperative restoring full bite. It's a sim0le design, but works very well.
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2011 SUNDANCE B20CCR SKIFF, 2011 YAMAHA 90HP 4 STROKE, 2011 KARAVAN SINGLE AXLE ALUMINUM TRAILER, LOWRANCE ELITE-7 HDI, MINN KOTA RIPTIDE TROLLING MOTOR
2000CC HYDRA-SPORT 225+HP EVINRUDE SOLD 
AND THE PINK JEEP!!!! R.I.P.
http://www.wellcraftv20.com/communit...ad.php?t=11664
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