Looking for insight as to squeal under engine power

[Baysider]

I'm kind of at my wit's end regarding a problem I'm having and thought maybe somebody has had this problem and could steer me in the right direction. I get a loud squeal/whine, when I am under engine power, when my motor is at or above about 2000 RPM.  However, when the engine is ramped to and past 2000 RPM while tied to the dock there is no squeal in either forward or reverse.  It would seem the only difference between moving through the water and being stationary is in the motion of water past the prop. I'm using a 3-blade 15 x 9 prop. 

Our mechanic does not think it's the v-belt, which is about two years old, and appears to be properly tightened and not slipping.  This spring our mechanic replaced the very worn cutlass bearing, but no change. 

It doesn't seem to be related at all to rudder vibration.  Help!

[KWKloeber]

https://c34.org/bbs/index.php/topic,11467.msg92521.html#msg92521

[Baysider]

Thanks KWKloeber, but the link takes me to a thread about muffler/exhaust pipe issues.

[Noah]

I believe that was his way of asking you to please tell everyone what engine you have on your boat.

[Kyle Ewing]

Are you sure it's from the engine and not the prop or something else?  I sometimes get a sqeel which I traced to the prop.  See https://www.cruisersforum.com/forums/f114/singing-prop-what-to-do-15445.html.

[Baysider]

Thanks Noah and KW.  The engine is the original Universal Model 25XP.

Kyle:  I'm not sure of anything at this point.  Our mechanic thought it could be the cutlass bearing, based on listening in the aft berth under way, but which he changed to no effect.  He also realigned the engine.  I was thinking maybe it was related to the prop, especially since the noise occurs when the prop is pushing the boat but not when the prop is engaged at the same RPM and the boat is held stationary.  It would seem the flow over the blades would be different, but I haven't been able to figure out what the difference (pressure difference leading vs following side) might be.

Thanks for the comments.

[KWKloeber]

Check this thread. It was on an m25/mk-I probably w/the same transmission?

https://c34.org/bbs/index.php/topic,11396.0.html
If your mechanic hasn't done it use the dowel technique to try to narrow it down.

We don't know what/if he narrowed it down as he didn't report back the results (that I recall seeing anyway.)
Dunno.  Maybe he got fed up and sank her for the insurance?
Good luck!

[glennd3]

Take the belt off and see if you still have the squeal. You can run the engine without it for 5 minutes or so.

[waughoo]

^---- EDIT ----^

As long as the engine is cold to start with.  5 minutes when it is hot would be a stretch.

[Ron Hill]

Bay : What prop do you have??  Standard from Catalina or another?

A thought

[Baysider]

I'm a little uncomfortable running without a belt and am pretty sure that it's not the problem, mostly because the PO said the squeal was not a new issue (they replaced the alternator and belt about 2 years ago and the noise preceded the replacement).  They claimed all diesels had a sweet spot and that the engine liked to run below 2000.  The surveyor didn't see this as a problem, and I had no experience with diesels, so I foolishly accepted the explanation.  Mostly the fact that the squeal doesn't happen when the boat is immobilized and the engine is run well past 2000 rpm in forward argues against the belt as the culprit.

[waughoo]

I havd experienced props singing at certain speeds.  Your assessment that it isn't the belt jives with my troubleshooting (would make it at the slip or underway if it was the belt).  Sadly, I cant recall what the solution ended up being for the prop sing.  You might want to enquire with a reputable prop shop in your area and ask them about it.  They would likely know what to do.

[Ron Hill]

Bay : Can you get the boat moving with the engine over 2000rpm and the squeal sounding, quickly reduce power shift into neutral and then advance the power to over 2000 rpm?  Squeal or not??

It almost sounds like the transmission???  Try a stethoscope or a long handle screw driver in your ear when squealing!!

A thought??? 

[Noah]

Sounds like no fun to get your head with a stethoscope attached down onto the tranny while underway in gear. Please be careful!

[Stu Jackson]

............
They claimed all diesels had a sweet spot and that the engine liked to run below 2000. 
............

WADR, for our engines (I have an M25, yours is the M25XP, essentially identical except for 3 extra HP and the bigger HX), that statement is nonsense.

My WOT is 3000 rpm, and yours should be, too.  I run anywhere between 2400 and 2650 usually, and on our trip up the west coast in 2016 from SF to BC I ran at 2800 for days on end.

As others have suggested, it would be helpful for you to do some investigation on your own.  Get a friend to drive your boat and spend some quality time down below listening, using the techniques suggested here by others.

In reading your comments here, I kept internally reacting to your repeated "...my mechanic said or did..." like fingernails on a blackboard. Maybe it's just me, but having someone else work on your boat also requires that YOU know what he's doing.  IMHO, the only reason to have someone else work on your boat is if you're unable to physically perform those tasks.  If you can, learn how to do so, it might save your bacon when your "mechanic" isn't available, like when you're out cruising.   I've had "others" work on my boat twice (in the past 25 !!! years).  In both cases, I've had to fix their "repairs."  I learned to do my own work.  You can, too. 

One other thing: that noise could be your prop.  Have a prop shop look at it with a short haul.  Experience indicates that a little feathering of the edges of the prop can make the noise disappear.

Good luck, please keep us posted.