[C320-list] tach issue

[Dean Vermeire]

Just a wild thought here, but is it possible you are cavitating?  I've 
never had that happen with a sailboat, but certainly have with a motor 
boat (it was someone else's boat and they forced me to go with them!).

Jamie Pett wrote:
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> List - I had an odd tachometer anomaly this weekend and wondered if
> anyone can shed some light ?
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> While motoring home I was monitoring the tach - always try to run at
> 3100 -3200 rpm which I understand is correct cruising for my motor-
> Yanmar engine.  The tach would be reading 3100, and with no noticeable
> change in the motor sound / speed etc. would drop to 2800 or so.  Once
> or twice it jumped up to like 3400, and I found myself throttling down,
> then my speed seemed slow.  ( To make matters worse, my speedo is not
> working, and sender is not fouled - guess the sending unit went bad ? So
> I am relying on gps for speed which jumps around a bit.)
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> Does the tach. Run off the alternator ?  Could the problem be a belt ? 
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> Any thoughts on why this would happen ? 
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> After running for 20-30 minutes, I go the rpms settled at 3100 and
> stayed there steady all the way the home - 2 plus hours into Sunday's
> non-existent wind.
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> Any insights appreciated - 
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> James Pett
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> 'Bella Luna' #614
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