A friend had the same issue, the problem was apparently that the water flow over the prop was neutral/reversing when the boat surfed momentarily. His solution, after much dollar spendage and mechanic guessing, was to motor at a speed that didn't produce the problem.
Jim Watts Paradigm Shift C&C 35 Mk III Victoria, BC On 16 June 2016 at 09:50, S Thomas via CnC-List <cnc-list@cnc-list.com> wrote: > I wonder if that little bit of wind was just enough to tilt the boat > forward so that the prop was sucking air momentarily as the bow tipped down > over the top. Could that cause the prop to feather? Power boat racers have > a person assigned to the throttle in swells. I don't have a feathering > prop, just speculating out loud. > > Steve Thomas > C&C27 MKIII > Port Stanley, ON > - Geared Gori prop > > ----- Original Message ----- > *From:* Andrew Means via CnC-List <cnc-list@cnc-list.com> > *To:* cnc-list@cnc-list.com > *Cc:* Andrew Means <andrew.cnc...@gmail.com> > *Sent:* Thursday, June 16, 2016 12:25 > *Subject:* Stus-List intermitent vibration/shudder in ocean swells > > Hey all - > > My friends and I are currently in Tofino, BC on day 6 of a much needed > vacation. So far our Yanmar GM30F and 3-bladed max-prop have been > performing brilliantly, sipping diesel and pushing the boat through the > less-windy sections of Strait of Juan De Fuca and up and over some large > ocean swells on our way up to Tofino. > > Yesterday on the way up from Ucluelet I felt a shudder/vibration as the > boat crested a swell. It was short but pronounced. The motor didn’t change > RPM at all or seem under load. About 10 minutes later it happened again, > also over a swell. This time we had to lower the RPM of the engine and let > it idle - when we brought it back up it was smooth again. This happened > maybe 6 times over the course of the passage, always starting as we were at > the top of a swell. > > We’d been going through swells at the same angle under power the day > before with no trouble, the only difference this time was that the little > wind there was was behind us. > > The only thing I can think of is that one of the blades of the max prop is > feathering as we go over these swells. I have no idea how one would fix > that - or if there’s any way to do so without hauling the boat out (hoping > to avoid that mid-trip…) > > Any ideas? > > -- > Andrew Means > S.V. Safari - 1977 C&C 34 Mk I > Seattle, WA > > ------------------------------ > > _______________________________________________ > > 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! > > > _______________________________________________ > > 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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