Prop noise?

[seabreeone]

I Purchased a Ericson 35 mark II a few months back. It had many issues one was when motoring a wobble and noise sounds like wood rattling & metal grinding sound that seems to be from stuffing box. I replaced the bad cutlass bearing. Replaced the leaking packing. Replaced the transmission that had bad bearings last owner never filled it with fluid. Had mechanic align shaft.It was way out. Now at 5 knots the boat feels great. Quiet and smooth. at 5.5 knots + I get this little vibration and loud sound like wood rattling with the vibration. I can feel it in my feet. I checked all the bulkheads and for loose items all seems secure. If I bring it to the dock tie it up put it in gear and rev it up no wood sound. It is just under way. Maybe a slight bend in the prop and cavitation?The mechanic said If it was a bent prop shaft it would do it at the dock also. Anybody have a issue like this before?

[model 10]

Our boat does it also. I've looked at and changed almost everything and finally believe it's the prop, cavitating perhaps.

[Rapanui]

If there is some play in the rudder bearings, it could be the rudder. Propellers produce some rotational flow and turbulence which can excite the rudder laterally.
If you have a P bracket, its not unknown for the bolts securing to the hull to work loose.
It may be slight, but these things drive you mad until you find a rational explanation.

[a64pilot]

Seriously doubt cavitation at our speeds and RPM, seems like there are harmonics set up in my boat at certain RPM's, my Yanmar manual sort of eludes to this and says to avoid those RPMs that cause vibrations, for me that's usually about 1500, haven't tried it at the dock, but would think it would be different as the prop is much more loaded when there is no vessel speed

[GordMay]

Greetings and welcome aboard the CF, Seabreeone.

[seabreeone]

Thank you all your great, This issue is driving me NUTS.I think it is harmonics but I am lost.... They say sailing is fun???? It is but the motoring (When not 100%) leaves a lot to be desired.....

[SkiprJohn]

Is it at all rpms or just one certain speed that it occurs?

Can you get your arm and hand on the shaft and try to force it to wobble? Of course, that would be while in port and engine not running. Try shaking everything from engine all the way back.

[delmarrey]

Originally Posted by a64pilot

Seriously doubt cavitation at our speeds and RPM, seems like there are harmonics set up in my boat at certain RPM's, my Yanmar manual sort of eludes to this and says to avoid those RPMs that cause vibrations, for me that's usually about 1500, haven't tried it at the dock, but would think it would be different as the prop is much more loaded when there is no vessel speed

Actually, with a boat tied to the dock there is LESS load. The water just circulates in a circle under the boat. And the boat is not being forced thru the water. It's not like an airplane. If the propeller were able to go fast enough it would cavitate.

It'd be similar to a raw water pump running with the thruhull shut off. But that's an extreme example. Water is dense.

Cavitation is caused by bubbles that form around an impeller or turn, usually from heat or vacuum. Those bubbles cause the degeneration of materials in its path. You should see what happens to valves and pumps at the bottom of a dam when they start to leak.

I'd check the rudder bearings for looseness.



.

[nicholson31]

when I first was purchasing my boat I noticed a vibration at higher rpm and things began to rattle a bit. Yard mechanic checked it out and discovered two broken mount plates. Put in new ones and issue is gone.

Also a little different scenario but last year I started getting a rattle and knock sound when sailing, If i put in gear it would stop, drove me crazy first thought a bearing may be getting sloppy in the engine but its only 4 years old, 3YM30 . It was surprisingly loud and could be heard above the radio and throughout the boat and felt at your feet in the cockpit. You would also hear a metallic like bang when selecting gear though not loud. Finally I had to dive down and check it out and discovered the prop anode was loose due to being eaten away around the retaining bolt causing it to rattle and vibrate as the prop rotated. Anode is on the prop nut.
I changed the anode but it happened again with new anode after a month. Yes there is an issue at our marina in one particular area with electrolysis. This year I put some heat shrink on the bolt where it passes through the anode and it has solved the problem. Just hauled out after 4 months and other than normal pitting on the anode surface, the bolt bore stayed intact keeping the anode nice and snug, no rattles.

[Cheechako]

Bent prop. Prop wash and loose rudder. Prop too large... tip too close to hull. Motor mount. all are possibilities.
Often a motor mount can look fine but be completely loose rubber from the steel. Watch each mount and have someone put it in gear... see if the engine moves up and the mount is bad.

[seabreeone]

Hi All thanks for your help. Today I spoke with the mechanic. He told me Porp shaft looks fine motor mounts are ok He said a bit soft but should not be a issue. He seems to think it is a harmonic sound maybe from the mounting of the engine? He said that it can be coming from any place and your feel it in your feet and hearing it? Today I checked everything I could find to see if something was loose? All looks fine and very solid. I did notice that the rudder leaks when motoring. I will change out the packing next week. When I replaced the cutless in the yard I shook the rudder and It had no play in it. Bearing seem to be OK? but I really don't know how to check them? My mechanic said harmonic issues can be very hard to find. He will be going with me on a trip around the block soon and I hope he can find it? This is my forth sailboat in 40 years of sailing and I have had some type of issue with each one. But this is the worst and driving me crazy...
So any type of advice from you all will be greatly appreciated. Thank you all for your time and wisdom...Rick