Prop Sing

N

nordski

Member
Joined
May 14, 2012
Messages
9
Fluid Motion Model
C-24 C SE
Vessel Name
Tug O' War
I have a 2014 21-EC that was in for bottom paint last month. The shipyard said I needed to have the cutlass bearing replaced. They performed the work and after getting the boat back in the water it has a high pitch resonance at 1500 RMP. I called the shipyard back and they say it is "Prop Sing". They claim it is very common and seemed surprised that I did not have that sound previously. The sound goes away 100 RPM on either side of 1500 RPM but is very annoying and rather loud. Never heard this sound before. The shipyard says it may be possible to fix the problem by sending the prop in to have a 45 degree bevel ground into the leading edge. Has anyone come across this before?
 
Bumping post delayed in moderation queue.
 
Prop sing is not that uncommon and a lot of information on the web as to the cause and how to fix or eliminate the prop singing. I would research prior to paying out more cash! What they told you is correct but you should know what your other options are. Bob
 
Hi nordski... Don't want to derail your post regarding "prop sing" but was curious as to how many hours your have on your engine as you noted that the yard recommended changeout of the cutlass bearing? Did they tell you what the amount of movement was or did you witness the amount of play yourself? What brand name of cutlass bearing did you use as a replacement? Replace in kind or used another supplier?

The only reason I ask, is than I recently replaced mine (2014 21EC as well) with the original type because I was changing out the engine mounts and decided to do both at the same time. I could feel "some play" at the cutlass bearing. My best efforts to measure play was .060" to .070". After replacing the bearing I still had roughly the same amount of play with the new bearing. I had 2345hrs at time of changeout.

Sorry again for the derail. I am not familiar or had heard of "prop sing" before, so something else new to me, but as one of my old boss used to say," If you don't learn something new everyday, you aren't listening".
 
Thank you Bob for the input. I will start looking at my other options.
 
Newf":2ygt6tbt said:
Hi nordski... Don't want to derail your post regarding "prop sing" but was curious as to how many hours your have on your engine as you noted that the yard recommended changeout of the cutlass bearing? Did they tell you what the amount of movement was or did you witness the amount of play yourself? What brand name of cutlass bearing did you use as a replacement? Replace in kind or used another supplier?

The only reason I ask, is than I recently replaced mine (2014 21EC as well) with the original type because I was changing out the engine mounts and decided to do both at the same time. I could feel "some play" at the cutlass bearing. My best efforts to measure play was .060" to .070". After replacing the bearing I still had roughly the same amount of play with the new bearing. I had 2345hrs at time of changeout.

Sorry again for the derail. I am not familiar or had heard of "prop sing" before, so something else new to me, but as one of my old boss used to say," If you don't learn something new everyday, you aren't listening".
Click to expand...

Newf.....no worries, glad to share my story. The boat has only 200 hours but had been sitting for years. Not sure if that was the cause of the failed cutlass or not. My boat was in for bottom paint and the shipyard called with a recommendation to replace the cutlass bearing. That shipyard is supposed to be the best one around so I agreed. Apparently they had to remove the rudder linkage and shaft to access the bearing. Everything was so frozen up on the boat that it was very involved to get the housing and bearing out. They replaced with a stock bearing. I was working out of town at the time but I should have looked at it myself at the shipyard to see if I was given correct information. I'm embarrassed to say what I paid for the work, hard lesson.
 
Usually a gap up .010 on a feeler gauge is max clearance. A big telltale sign is a banging when changing gear from forward to reverse.
 
HI Nordski,

I have the same prop sing on our 2015 R-21EC. It happens at a few RPM levels and takes about 100-200 rpm over to get it to go away. I hadn't heard about prop sing until this post, thanks for sharing!
-Steve
 
That was HOP SING, aka Victor Sen Yong, damn I love bar room tid-bits. -Bob
 
Turns out that "prop sing" occurs when the edges of the prop blades are too square with the water. Sharpening the blades will remove. The local prop guy told me I had a ski boat prop on the boat, it is the factory Acme 4 blade prop. I spend the $ to get what he recommended and very happy with the results. 13x12 3 blade....balanced, top speed 8.1kts.
 
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