Unusual Noise??

[John]

We have a 1986 Catatina 27, yesterday my wife and I took her out for a spin in the Gulf. While in the cockpit and running the engine, we noticed that there was a new noise that sounded like a high pitched "whine" coming from below where our 14 horse Universl diesel is. We only heard this new noise at speeds of about 5.2 and 6.1 knots. The other speeds we did not notice the new noise. Can anyone tell us if they have ever had this problem or heard this kind of noise? Thank you much in advance...

 

[Bob]

Unusual noise

I have a friend with a Cat 36, 25 hp diesel that does the same thing. My 30 doesn't. However my son-in-law who is a lobsterman with an enormous Caterpillar diesel engine also does it. One opinion is the trailing edge of the prop is either too sharp or has a rough place in it. Don't know if that id really the cause. Ask around, I'll bet others have the same problem.

 

[Rob Rich]

More Info

A couple of questions:Does the noise happen at those speeds regardles of RPM? Idle or foward? Both?If you horse the engine from a dead stop, can you replicate the noise at higher or lower boat/engine speed?Do you have access to the engine bay from above, so that your wife can run the boat at that speed and you can crawl down on top of the engine and isolate the location of the noise?If you look at these three areas, especially the last, you may find the answer. I think the main obstacle is finding out if the noise is coming from the engine or the drive assembly. Then, you need to isolate the sub-part from which it eminates. Could be a prop (cavitation), out of balance shaft, misaligned engine, stuffing box, transmission, or engine itself. My 27 squeaks when the stuffing box is dry.