Volvo D1-30 R21-EC Cavitation?

[tjcouch]

I am a new owner of a 21-EC, tug is a 2015, engine was replaced in the recall in 2018, Volvo D1-30, 80 hours.

I am also a first-time owner of a displacement vessel.

My issue is that I am hearing what I believe to be cavitation above 2200 RPM, with the sound becoming more intense, and frequent with increased power.

The sound can best be described as gravel being crushed. The occurrence of the sound does not have a rhythm. Nearing WOT the sound is accompanied by a slight loss of power/speed.

A knowledgeable inboard sailing yacht owner, engineer, and retired submariner, brought over his stethoscope and listened to the engine, mounts, shaft and bearings, and suggested that it was cavitation, but did not seemed to be concerned by it.

The prop shows no signs of wear, or play in the shaft, however it does have a coat of antifouling.

I welcome your thoughts.

To me, it "just does not sound right."

 

[bob daily]

Tjcouch
You did not say if you had a three or a four blade prop and what the pitch angle was.
There is a lot of info on the internet about (disc area ratio) DAR and cavitation. I see that you keep your boat on a lift so getting info and inspection of prop and shaft will not be a problem.
Good luck and keep us posted. Bob

 

[tjcouch]

4 blades, unsure of the pitch. 3K RPM is open throttle.

 

[bob daily]

Not that much different RPM than my yanmar, I would check with ranger tug, Kent ,Washington with prop info: ie size, pitch,etc, and verify its correct! Sounds like something is going on and it's better to err on the safe side, and get you back in the water.
Best of luck! Bob

 

[NorthernFocus]

Based on the qualifications of your buddy I'd take his word for it. He's also correct in that it's not likely to do any damage. At least not for several hundred hours of operation. It's more of an annoyance than anything. If it only does it when there's a bit of chop on the water then it is likely aeration rather than true cavitation. In which case a different wheel won't help.

 

[M&H]

I had exact symptoms you are describing, as the prop zinc wears a bit it is not tight against the prop and will make that noise, can’t quite tell in your pic but looks like it could be at that point

 

[tjcouch]

I had exact symptoms you are describing, as the prop zinc wears a bit it is not tight against the prop and will make that noise, can’t quite tell in your pic but looks like it could be at that point

Absolutely fantastic! I replaced the anodes this morning, and also removed the bottom paint from the prop.

It sounds so much better now, and I gained about a knot at WOT.

Thank you, thank you, thank you!