Prop noise at high engine RPM?

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ceaves
Posts: 10
Joined: Wed Dec 31, 1969 8:00 pm

Prop noise at high engine RPM?

Post by ceaves »

Our J/109 started making a strange noise at high engine RPMs. The mechanic sea-trialed it today, and came back with a few thoughts, and I am curios experience of others.

He said the engine and sail drive were fine. He though the cavitation / vacuum noise might be coming from the prop. I believe the prop is original to the boat, but I can't be 100% sure. It is a two-blade folding one. I also had the diver last week look at it, and he seemed to think it was fine.

The mechanic thinks either the prop is "wrong" for the boat (too small, pitch too low, not enough cup) or the prop is slipping on the shaft. His reasoning for this diagnosis is that the engine goes to 4200 rpms at full throttle. He thinks it should only go to max 3600 rpms.

Just curious, on your J/109 what is the max rpms of the engine at full throttle? Do you have the original prop?

To be clear, the boat has not done this in the past, and this sound is new, so I doubt the prop is wrong. I have never heard of the prop slipping, but maybe?
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Vento Solare
Posts: 394
Joined: Wed Dec 31, 1969 8:00 pm
Location: Newport, RI

Re: Prop noise at high engine RPM?

Post by Vento Solare »

I doubt the prop is slipping as there are splines on the hub and shaft. More likely the clutch in the sail drive is slipping.
Dan Corcoran
Posts: 280
Joined: Sun Jan 29, 2017 4:32 pm

Re: Prop noise at high engine RPM?

Post by Dan Corcoran »

Don't believe it. The engine controls are showing 4000 rpm on Strider, not at full speed, motoring around 6kots. Starting a few weeks ago. Clearly over reporting.
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Vento Solare
Posts: 394
Joined: Wed Dec 31, 1969 8:00 pm
Location: Newport, RI

Re: Prop noise at high engine RPM?

Post by Vento Solare »

I missed the 4200 rpm comment. No way the Yanmar does that. Get a hand held tach and calibrate your instrument panel tach. You can buy a laser tach on ebay for less than $15 and they are very accurate.

Here is a $15.99 Tach on Amazon similar to the one I bought on ebay. It comes with a case and reflective tape you put on the crankshaft pulley.

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