Thanks Andrew, Joel and Mike. That Martec is the same as what I took off in 2002. Never did make 7 kts with that, though do not recall ever trying. The tach did not work when I had the Martec so have no readings for comparison.
Am not by any stretch a mechanic. According to the Yanmar manual the “continuous rating” is 3400 with the “one hour rating” of 3600. I usually operate the engine ~ 2750-2800 which is just over 80% of continuous and 78% of the one hour. Have heard for years that 80% is the rule of thumb for diesels. The 3200 delivery trip this spring was a one off aberration due to time constraints. Do not think I could even get to 3600 if I wanted to. And from what I have read the engine “should” be able to reach that, just not be operated at that level for a period of time. That said, still have some pitting on the prop blades and more vibration than can be good. Both signs of cavitation. Even at 75% of continuous [2550] have vibration. Have had the engine mounts replaced after I replaced the prop shaft and coupling in an effort to mitigate the vibration possibly due to a bent or out of balance shaft. Everything was aligned by a mechanic who has a good customer base, so assume was done correctly / accurately. A friend has a sister ship and easily gets to and cruises at 7+ kts and I can barely make that only when really press to WOT and never do that. He also has a Flex prop though the “racing” version which has smaller blades. Have asked him to check his diameter and more importantly pitch. All this has led me to conclude that my prop is over pitched. From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Andrew Burton via CnC-List Sent: Tuesday, July 21, 2015 10:42 AM To: cnc-list@cnc-list.com Cc: Andrew Burton Subject: Re: Stus-List Best Engine>Yanmar 3GM + Prop? It sounds to me like you may be over-revving your engine. My rule of thumb with my boat (same engine as you) and when I get on a boat I'm delivering, is to get into open water and, in gear, push the throttle wide open. My cruising RPM is no more than 75% of that number, which on Peregrine works out to 2200 or so. Andy C&C 40 Peregrine On Tue, Jul 21, 2015 at 10:31 AM, Nauset Beach via CnC-List <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> > wrote: 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:cnc-list-boun...@cnc-list.com <mailto:cnc-list-boun...@cnc-list.com> ] On Behalf Of Hoyt, Mike via CnC-List Sent: Tuesday, July 14, 2015 12:39 PM To: cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> 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:cnc-list-boun...@cnc-list.com <mailto:cnc-list-boun...@cnc-list.com> ] On Behalf Of John and Maryann Read via CnC-List Sent: Tuesday, July 14, 2015 8:19 AM To: cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> 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
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