Quote:
Originally Posted by Cheechako
The shaft will not become loose when you unbolt the coupling. It is very true that , although you may be out of alignment, it isn't necessarily the vibration problem. My 47 footer had a Nanni/Mercedes engine that at about 1500 rpm had a harsh vibration throughout the boat. It was not an alignment, bearing or motor mount problem. Nature of the beast I guess. I just avoided that rpm, but you have to pass through it going up and down.
Your problem sounds like a new one though, and hopefully it is that alignment.
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Same thing with my
boat. Alignment is perfect.
Smooth until 2200-2600 where it's unbearable. Of course, that's exactly the range in which I usually wish to
motor.
The stern mounted
barbecue rattles so much it seems to threaten to jump
overboard.
Above that RPM range, smmoooooth again.
I used my Fluke ScopeMeter and an old speaker as a microphone just above the prop in the stern compartment
deck. I measured the frequency of the vibration and proved it was resonance of ihull because the vibrarion was 2x the propshaft rpm which I measured by the tachometer divided by the
transmission ratio. The 2x is because it's a two blade folding prop.
A friend suggested pouring concrete into a hole drilled in the aft
deck.
Yeah right ! Concrete in the stern of a
multihull? I'd rather deal with the vibration.