Maxprop Noise

[Eddie]

I recently replaced a 17 inch fixed 3 blade with a 18 inch 3 blade maxprop classic. It produces a whirling,gurgling noise that sounds like water turning under the hull. It does this at 1200 to 1900 rpm's. Seems fine below and above this band. A mechanic rode with me and thinks it is cavitation, he doesn't hear any noise from other components of the prop shaft. I am somewhat overproped,max rpm should be 3600 and I can only get 3100. The motor is Yanmar 4jh2te with Kanzaki km4 transmission. I get the noise either in forward or reverse. Has anyone experienced this problem? Do you think reducing the pitch to get 3600 rpm's will solve the noise problem? I think I have at least 15% tip clearance . The noise is loud enough not to "put up with it" Thanks for any help
'

[Paul L]

Give PYI a call. They know the prop well and always available to give you advice on it - even if you bought it used.

Paul L

[speciald@ocens.]

You are probably over-propped. Ask PYI.

[Eddie]

I did talk to PYI. They were very nice to talk with and did suggest repitching. They were not convinced that the repitching would correct the problem but thought it should be the first thing to try.

[senormechanico]

Maxprop blades have no twist so they can have low drag under sail.
This causes a certain amount of cavitation under power.

[bluzzin]

If you can only get to 3100 rpm you are over propped. Have your diver change the pitch or do it yourself. PYI can help with finding a diver who can do it for you in the water, if you don't want to do it yourself.

michael

[ronbo1]

I have a 19" MaxProp and also get some noise at low RPM.
Senormechanico may be right with cavitation as the cause. Unless it occurs at your preferred cruising speed you may have to tolerate it.

Ronbo

[lancelot9898]

I have a 17 inch max prop and I know that I'm over proped since I can't reach the rated rpm of the engine. However, I've never experienced in the 25 years of using that prop the noise that you've described. My first thought when I read this thread was that maybe the prop is not filled fully with the proper grease, but then PYI should have mentioned this if that could be a cause.....so I'm not sure.

[sded]

Did you cut the end off of your shaft to match the taper of the MaxProp? If so, you may need to modify the fore-and-aft alignment because of the changed propeller position.

[senormechanico]

We had the noise at 6 knots (sounded a little like grinding gravel) but if we backed off to 5.5 it went away. I'm quite sure it was cavitation. It wasn't horribly loud, just there.

[Eddie]

I am doing a quick haul in a week or so to change the pitch. I will also be checking alignment,greasing and such while the boat out of the water. Thanks

[fstbttms]

Originally Posted by Eddie

I am doing a quick haul in a week or so to change the pitch. I will also be checking alignment,greasing and such while the boat out of the water. Thanks

Again, all of this can be done with the boat in the water. FYI.

[gettinthere]

I am truly amazed that divers can do this under water. I have a hard enough time doing it on land!!
I assume you rig a catch net below your work space?

[r.furborough]

As you have increased the diameter of the propeller you are probably hearing more prop-wash on the hull immediately above the propeller. There is a rule-of-thumb that there should be at least 15% of the propellers diameter as clearance from the propeller blade tip to the hull.

[Eddie]

Can they repitch the classic maxprop underwater or only the vip prop? Does seem hard to do underwater.