2015 R21 whine

[ohioan55]

I'm seeking wisdom from your technical gurus. Our r21ec developed a whine last year. The whine is only present between 1100 to 1900 engine RPM, and only in forward gear. It will abate when throwing on rudder (sometimes). First thoughts was the cutlass bearing. First, I checked the engine alignment (twice). Looked to be in tolerance, so I towed it to the local yard (also the Volvo Penta folks in the area). They swapped out the cutlass bearing, but the whine is still present. They also did an engine alignment after the boat had been back in the water a few days. The tech who was there said it was the transmission, so I pulled the boat again and returned it to the yard.

The yard pulled the transmission, did not see an issue, consulted VP corporate. They recommended replacing the harmonic dampener. After replacing the part and reinstalling, the whine was still present (no change). So the transmission was again removed and set off site to be rebuilt. The unit came back, was reinstalled, and the whine was still there. The transmission was pulled for a 4th time and sent to the offsite rebuild facility, where they replaced all bearings. The unit was returned, re-installed, and upon testing the whine was still present. Every part from the back of the engine to the prop has been removed, inspected and/or replaced, and reinstalled multiple times. After discussing the situation with the yard, we decided to just run it and see what happens. Do the factory folks have any ideas we can check, prior to me ordering an R23?
Thanks

 

[bob daily]

Prop sing! Look it up on the web, has been discussed on this forum in the past. Bob

 

[BB marine]

Bobs suggestion would have been my first thought as a servicing technician. When unusual vibrations or noises are present at speed and can go away by adjusting speed in most cases the running gear is the suspect. Prop, shaft or bearing. Prop inspection by a technician is not the best way to approach. Remove the prop and take it to a prop shop that scans and balances then tunes the blades based on the props application. ski boat, cruiser , trawler and sail boat. The prop scans and balancing using software technology brings the blades in so close that it could cause prop sing. The prop sing as I understand it is caused by harmonics from each blade. Many times this happens after a prop is rebuilt to perfect tolerances. But it can be caused from the blade tips. The singing is caused from propeller diameter and Rpm's, Boat speed and Trailing-edge size (thickness) and roundness. Diameter, Rpm's or speed are not easy to change , modifying the edge geometry can be changed easily without changing performance. Good Propeller shops and servicing technicians are familiar with the Antisinging edge or Chamfering of the Trailing edge, on the suction side. The intent of this shape is to avoid water disturbance flows by cleanly separating the flow off of the blade.

Many times from erosion of the blade tips this singing will start to occur. As a working marine service technician if I pulled a prop shaft for installing a cutlass bearing the shaft was placed in V-blocks and runout checks were done, The prop was sent out scanned and tuned and new bearing was installed. If the boat had an issue that seemed like prop sing I would tell the prop shop to inspect the blades tips and adjust as needed. If the noise persisted I would notify the prop shop to see if more adjustments could be made to the prop. In most cases a prop that did not sing before can be adjusted to not sing again. If the boat/prop combination always had the issue then a prop change of blade diameter or number of blades may be done to eliminate the issue.

There is a big difference between prop sing and transmission noise!!! Yes the noise and vibration can migrate up the shaft to the gear but with some simple troubleshooting the gear can be eliminated or diagnosed as the issue. Run the boat in gear at the rpm that the sing is present. Using a mechanics stethoscope place the rod on the hull near the prop listen, next place the rod on the gear housing close to the output shaft listen. Pick a few other locations on the gear and place the stethoscope tip on the housing listen. Now uncouple the shaft coupling. This will eliminate the running gear from the equation. Place the gear in forward and run at the rpm where the sing was present. Using the stethoscope do the same checks on the gear. Did the noise change? The only difference to the gear operation is the thrust bearings are not loaded. A bad trust bearing does not sing or whine. it rumbles. It will sound rough when using the stethoscope.

Parts changers!!! Makes a noise take it apart until we find where the noise is coming from!!

Your issue could be as simple as cleaning the edges of your prop.

Rebuilding a reverse gear always includes replacing and shimming all bearings. When I did gear rebuilds the only parts that did not get changed were gears, shafts and pump if they inspected to specifications and all tolerances were within specs. Shims, bearings and seals and clutch plates were always replaced. The gear would be bench tested and then installed, pump pressures checked. If this is done there would be no issue with the gear.

Good Luck finding the issue. I am just posting my thoughts based on the information you provided.

 

[bob daily]

A easy check for Prop Sing is to change out the prop! A new prop is about $750-$1,000 if you can't borrow one! Not a bad price compared to what you've probably spent on shop time this far for a problem not fixed, not to mention loss of use of the boat during the season. Changing out the prop is a easy DIY afternoon project, lots of you-tube vidioes on how to' s. I would save the money spent on shop time labor for that new boat! Most of the time you can get a refund for the old prop which makes the price a lot lower if not kept as a spare. Good luck. Bob

 

[ohioan55]

Thanks for the replies. Help is always appreciated in the corner. When the cutlass bearing was replaced, the prop when to a prop shop. I spoke to the guy they, and he said all looked good. As for the transmission, this is what the yard/service tech said was the problem originally, causing us to chase a possible non existing to the tune of over 4 grand. I always felt the sound originated in the shaft area, which led me to focus on the cutlass bearing first. After that was replaced, the sound was still there. Being an ex sub sonarman, I am well aware of prop sing as I have spent many hours listening to it from various ships. One note, I did clean the prop prior to this fiasco and treated with prop speed. During cleaning, I did clean up the dings on the ends with a little sand paper. maybe I should pull the boat and just ding the prop. As an added note, the prop speed did add over a knot to top speed with a more quiet run. And I did remove it to make sure that was not the issue.