Hi Bill,
Another possibility is that the forward gear clutch in your
transmission is slipping (chattering). This can happen if the shift
linkage is not pushing you transmission fully into the forward gear (I
assume it is a Hurth transmission). You can test this by going below and
pushing hard on the transmission shift lever (pushing it further into
forward gear) while it is vibrating. I am told this can create a severe
vibration. Your solution might be as simple as readjusting you shift
linkage.
Good luck,
Gary
S/V Expresso
C&C 35 Mk II
East Greenwich, RI, USA
On Thu, Jan 9, 2014 at 12:46 PM, William Hall <wh...@alum.mit.edu> wrote:
> Dear List,
>
> I've been troubleshooting quite a vibration problem since I got my boat a
> year and a half ago. I had hoped it all just needed an alignment, but that
> does not appear to be the case. I'm hoping that if I present the situation
> someone on the list may be able to point me in the direction of a fix!
>
> The boat is Starfire, my 1985 C&C 37. It has a Yanmar 3HMF. I believe it's
> the original engine, but was overhauled a few years ago. The previous owner
> said it was overhauled because it was no longer producing enough power.
>
> The engine drives a 2-blade max prop. There's a line cutter on the shaft.
> There's an R&D marine elastomeric coupling between the end of the prop
> shaft and the engine drive shaft.
>
> When I bought the boat, we noted a lot of vibration when in gear above
> about 1800 rpm. The surveyor thought it needed alignment and noted as well
> that the max prop had more play in it than it was supposed to. I hauled it
> that first winter, had the max prop sent back to max prop for overhaul, had
> new cutlass bearing installed, and when it all came back together in the
> spring found the same vibration as before. When running in forward, the
> prop shaft deflects significantly at higher RPM's (maybe 1" of wobble at
> the worst point along the drive shaft), and things shake in a way that
> can't be good. In neutral, as well as reverse, it runs smooth as silk
> right up into high rpms.
>
> I've since had a few engine / drive people look at it and try to figure it
> out. The shaft appears to be true. The alignment appears to be right on, as
> measured by two different mechanics. The elastomeric coupling was a bit
> worn, so we put a new one in. The engine mounts are substantial and seem
> good. The engine people think there's something wrong with the prop that
> the overhaul didn't fix.
>
> What does the list say? Is it the prop? Could there be something wrong in
> the transmission, say a thrust bearing or something? In flat calm I can
> get almost 5 knots without too much worry of breaking things, but into a
> sea or wind I'd really like to have the option to use more power. What
> would you try?
>
> Thanks in advance for the thoughts.
>
> Regards,
> Bill
>
> 1985 C&C 37 - Starfire
> Stamford, CT
>
> --
> William D. Hall, Ph.D.
> 203 653 2886 (o)
> 617 620 9078 (c)
> wh...@alum.mit.edu
>
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