Originally posted by Silver Fox
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I'm getting used to our new to us 1974 C&C 27 Mk II with A4 and original two-bladed prop. Have not had much flat water to experiment, and have not got around to optimizing the carb at idle and cruising speed, but I did install a tach. On the one run where I made some observations, I easily got to 6 knots at 1800 RPM but the stern exhaust tip sat just at or under the sea surface. Came up some when I sent the crew forward, and came up more when I eased the RPMs to 1400 at speed to 5-5.5. Temperature seemed to drop too when I did that, though that might have nothing to do with the exhaust tip dipping below the sea surface. Still experimenting.
The Mark II's have a shorter stern aft of the rudder than the later Marks, and a heavier stock rudder, so might be more prone to cockpit weight pressing the stern down. At cruising speed, a sailboat squats and the stern wave forms, bringing the sea surface up. In another post, I understand Don investigated and found that exhausting underwater does not affect back pressure significantly.
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