[C320-list] Engine/Shaft Noise and Vibration

[Dennis Harris]

The prop has not been balanced.  Also, I just re-read my original post, and 
there was an error....The vibration "does not" seem to increase 
proportionately in magnitude, but the frequency does increase with increased 
engine speed at higher rpms. But below 2,000, the situation largely 
disappears.  Also, with reference to the fairing material crack at the shaft 
strut, we repaired that area with a combination of fiberglass and epoxy.

Dennis Harris
C320
#694 Washington, NC

----- Original Message ----- 
From: "Irving Grunes" <igrunes at gmail.com>
To: <C320-List at catalina320.com>
Sent: Saturday, February 19, 2011 11:50 AM
Subject: Re: [C320-list] Engine/Shaft Noise and Vibration


> Has your prop been balanced?
> Irv #851
>
> On Sat, Feb 19, 2011 at 9:40 AM, Dennis Harris 
> <dharris02 at suddenlink.net>wrote:
>
>> Just curious if other C320 owners experience this.  I get a low level
>> noise/vibration at certain speeds, and always have the fear that, despite
>> what the mechanic said, the shaft may be striking the hull, but the
>> frequency doesn't seem right.  The boat is a 2000 model (#694) with 
>> Yanmar
>> 3GM30F engine and transmission with 2.21 reduction.  The sound is a 
>> little
>> like a very low level "whump, whump, whump".  The frequency increases 
>> with
>> engine speed, but at higher speeds, the noise is largely overridden by
>> engine noise and vibration does seem to increase significantly, so it may 
>> be
>> noise more than vibration.  The cutless bearing is snug and there is no
>> movement in the shaft.  However, in last year's haul out, on the forward
>> edge of shaft strut, a small crack had come in hull fairing material. 
>> The
>> three remaining sides around the strut were solid and there was no 
>> leaking
>> into the boat.  The four strut bolts were tight.  In previous haul outs,
>> this area was fine, and the noise/vibration that I have mentioned has 
>> always
>> been present through out the 10+ years that I've owned the boat.  There 
>> have
>> been no issues (abnormal, frequent wear) at the packing gland. At ~2200 
>> rpm,
>> the intermittent sound occurs roughly 100 times/minute.  With the 2.21
>> transmission reduction, this means that the sound occurs at a frequency 
>> of
>> once per 10 shaft rotations, so in my mind, I have attributed the
>> sound/vibration to be a harmonic of the combined system (hull, engine,
>> shaft, etc.) and suspect that it's something not to worry about. 
>> But....what
>> if?
>>
>> Do others experience this?  Is it a problem that needs to be addressed, 
>> and
>> if so, how?
>>
>> Thanks,
>>
>> Dennis Harris
>> C320 #694, Washington, NC
>>