Dave, What you are describing is the same thing that is happening on my 1985 33 MKII with Yanmar 2GM20. I have a folding martek prop and when I leave my slip the blades open (No vibration ) but anytime I slow the boat down like when I'm coming back to the marina and I throttle down while still in forward gear the blades Close ?? (I'll get a nasty vibration) and the only way to stop the vibration is to shift into reverse stop the boat and shift back to forward.
This is especially cumbersome when out sailing and taking down sails with forward momentum and when I run the engine and shift to forward, I'll get the nasty vibration, the vibration stops only when I shift to reverse until I completely get stopped and then I can shift to forward and no vibration. What I was planning to do was send the prop to martec for refurbishing at the end of this season; however, now after what I'm reading this thread I'm not so sure that is the right solution. When inspecting the prop before launch this spring, the blades easily opened and closed by hand. I'm now thinking that the problem may be with the shaft spinning to slowly or transmission not fully engaged. Sorry that I'm not offering any new solutions here but just commiserating. Tom Lynch Bayfield WI IndoIrish On Thu, Jun 16, 2016 at 10:48 AM, Dave via CnC-List <cnc-list@cnc-list.com> wrote: > Alan, > > My gear shift linkage is totally different with the cable coming in from > forward of the lever through a bracket. Its pretty obvious that I need only > to remove the lever rotate it 180 degrees and reattach it to make forward > be forward again. > > I'm guessing that if the vibration was due to misalignment, engine mounts, > bearing or bent shaft that the vibration would always be their and not only > after slowing down. The prop, which is what I thought the issue was, has > been replaces with a brand new geared prop and since a new prop didn't fix > the problem that's not it. > > I did find the following on the web; > > My prop opens easily by hand and when the blades are oriented properly the > lower one will hang down by its own weight. Given that data, I knew with > absolute certainty that if it spins, it has to open. The condition Bob and > Dyk are describing happened to me just after I reinstalled the engine after > rebuilding it and I had not adjusted the linkage properly. I would have to > rev the engine up around 1500-1800 and it would rumble and abruptly > "kerchunk" and churn water at the stern. Initially I thought that was the > prop opening, but knowing how loose the prop was I knew there was no reason > for it to be closed before that. So I looked at the shaft. When put into > gear, it would spin but so slowly that there wasn't enough revolution to > drive the boat. I pushed on the linkage lever on the transmission and wham > it fully engaged and the shaft started spinning like it should - much > faster. I realized the rumbling I heard was gears trying to mesh and the > kerchunk I had heard was the transmission popping into gear, not the prop > opening. I adjusted the linakge so now when I shift into forward, the boat > moves even at low RPMs. > > Dyk, Bob, I don't know how tight a brand new or recently rebuilt prop is > supposed to be, but a spinning mass generates quite a bit of force. The > formula for centripetal force is F=mv^2/r with m=mass of object, v=velocity > at a certain radius, and r= radius. A quick check of the numbers will tell > you that even at low RPM, there is easily enough force to open your prop. > Keep in mind that if it is so tight that it won't open, it shouldn't be > able to close either, so when sailing an open prop should be spinning like > mad and you can hear and feel that. If you can assure yourself that the > prop is opening and closing, the only other variable in the equation is the > RPM of the shaft. I can only speak from my own experience and what worked > for me but there is no reason I can think of for a clean, properly adjusted > prop to not open. It has been designed to open when it revolves. Good luck! > > > > Dyk Luben > > unregistered posted 09-13-2002 02:36 PM > > ________________________________________ > > I need to follow up on my propeller situation. After further study, I > found that indeed the propeller shaft was spinning too slowly. It was a > problem in what I called the transmission, but what the professionals call > the reversing gear. The clutch was worn out and no amount of linkage > adjustment would correct it. I had a new clutch and seals installed by Mack > Boring, and it works perfectly now. So if anyone assumes that their > propeller is not opening correctly, don't go buy a new prop like I did, but > check first that the clutch is fully engaging > > Since I had the transmission rebuilt it's probably not the transmission > itself but may be that the shift lever throw isn't long enough and its not > fully engaging. So, reversing the lever arm and checking to see if the > transmission is fully engaging (by shifting it into gear at the > transmission) is my next step. > > By the way, last night was the first time the sails were hoisted and the > boat sailed and we managed to win line honors and a second place finish > against others for whom its their 3rd race. > > Dave J > Saltaire > C&C 35Mk3 > Bristol, RI > ------------------------------ > *From: *"ALAN BERGEN" <trya...@alumni.usc.edu> > *To: *davidjaco...@comcast.net > *Sent: *Tuesday, June 14, 2016 10:50:10 PM > *Subject: *Awful Vibration > > Dave: > > This is how the shift cable linkage should look. The vibration could be: > prop out of balance, bad engine mounts, bad cutlass bearing, bent shaft, > prop blades not opening all the way. > > I replaced my folding, two blade Gori prop with a three blade Maxi prop. > Expensive, but well worth it. No vibration and good stopping action in > reverse. > > My engine is a 3GM f (20 hp). > > Alan Bergen > 35 Mk III Thirsty > Rose City YC > Portland, OR > > > _______________________________________________ > > This list is supported by the generous donations of our members. If you > like what we do, please help us pay for our costs by donating. All > Contributions are greatly appreciated! > >
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