Simple Rule of Thumb: If you can't get to max rated RPM, you're over-pitched. If you can get higher than max rated RPM, you're under-pitched.
Alan Bergen 35 Mk III Thirsty Rose City YC Portland, OR John, Mike and any others with a Yanmar 3GM30F What is the make, diameter and pitch of your props, and can you get to the one hour rated RPM of 3600? Back in 2010 I had an engine overheat alarm and discovered the coolant overflow tank was full and had an amount of oily substance mixed in. There was very little coolant left in the engine. The mechanic discovered a blown head gasket was the cause. The head was sent to a shop to be "rebuilt" and a few other parts replaced. Last month [just after Edd's engine woes came to light] I had another overheat alarm, and again discovered the coolant tank full and the same oil mix. Am assuming the head gasket is blown - again. The mechanic has not looked at it yet. Obviously, something is "wrong." The July edition of Cruising World had a timely article about props and stated an over pitched prop puts additional wear on the engine and can lead to cavitation. Nothing new there but started a possible theory. I have not had dark exhaust so did not think the prop was over-pitched, but there is some pitting on the prop blades so maybe there is cavitation and an over loaded engine. Also have excessive vibration so the clues seem to be going in that direction. I rarely take the engine up to 3000 RPM though did have a several hour delivery at 3200 this spring. Have never tried but do not think I could get up to 3600. [Have read the Yanmar tach's are not all that accurate and have not had the RPM's verified independently.] Still this seems to be another indicator the prop may be over pitched. I originally had a Martec folding 16 D x 14 P prop though after the lack of much reverse led to a "near miss" incident I replaced it in 2002 with a Flex-O-Fold with a 16 D x 13 P at the recommendation of Flex o Fold. The reduction is 2.61. Am thinking the increased surface area Flex prop is overloading the engine even though the pitch was decreased by 1" compared to the Martec. Anyone have any thoughts? Thanks, Brian -----Original Message----- From: CnC-List [mailto:[email protected]] On Behalf Of Hoyt, Mike via CnC-List Sent: Tuesday, July 14, 2015 12:39 PM To: [email protected] Cc: Hoyt, Mike Subject: Re: Stus-List Best Engine? We have Yanmar 3GM30F in our Ferrs 33 which is similar hull shape to C&C33-2. We make 6.2 at 2300 RPM and can just squeak out 7.0 at WOT Mike Persistence -----Original Message----- From: CnC-List [mailto:[email protected]] On Behalf Of John and Maryann Read via CnC-List Sent: Tuesday, July 14, 2015 8:19 AM To: [email protected] Cc: John and Maryann Read Subject: Re: Stus-List Best Engine? HI Brian Our 34 has the Yanmar 3GM with Martec folding prop. Clean bottom cruising is 5.5, max is about 6. As I recall, your max speed is supposed to be about 80% of theoretical hull speed with throttle wide open?? Another variable is the calibration of the knotometer and if using the GPS the impact of current John and Maryann Legacy III 1982 C&C 34 Noank, CT ----- Original Message ----- From: "Brian Morrison via CnC-List" <[email protected]> To: <[email protected]> Cc: "Brian Morrison" <[email protected]> Sent: Tuesday, July 14, 2015 00:47 Subject: Stus-List Best Engine? > Hello, > > I often sail with a group of sailors that have more modern and > somewhat larger boats than my 1979 C&C34. When there is no wind and we > are forced to motor I have difficulty keeping up. With a clean bottom > my cruising speed is about 5-5.5 knots. I have an Atomic 4 engine. I'm > wondering would > a Yanmar or a Westerbeke give me 7+ knots? > > Brian C. Morrison
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