Intermittent Vibration...HELP PLEASE

[Chick Weiss]

I've had an intermittent and troubling problem. I've never been able to demonstrate it to a mechanic (even after hours of motoring around), but it happened twice again yesterday. Here's the problem...I'm motoring along and the engine or trans or drivetrain (I'm not sure where the source of the sound originates) radically changes its sound. There is a loud vibration seeming to come from the aft and some screeching occasionally. If I lower the throttle, it goes away but will eventually return in minutes, days or weeks later. When motoring, recently there is a high pitched sound, as well...this occurs regularly now.Yesterday, when I shifted from neutral to forward, it happened and I felt the vibration below my feet at the helm and the sound seemed to be in that area. The engine, however, does seem affected (but it's hard to tell since the sound is quite loud). When I returned to neutral and then shifted back to forward all went well for the rest of the day. I'm now wondering if rather than engine or trans problem (which 2 mechanics swear are in excellent shape....even as of last week when I had them motor with me), the problem is the cutlass bearing. Today I had a diver check the strut and cutlass bearing....the strut is ok but he feels some moderate lateral movement in the bearing....but he did not hear metal hitting metal. In addition, he pointed out that usually the prop (I have a 3-blade)on most sailboats is about 1-2 inches aft of the strut....but mine is 4-5 inches aft. The boat came with a dripless seal and he suggests that that may account for the length. But, he wonders if the vibration is due to this extra length under certain circumstances.Simply put....This problem is really interfering with our sailing season and when it happens, it really causes anxiety in our guests and makes my wife and me concerned about sailing any great distance. YOUR ADVICE IS GREATLY APPRECIATED.Chick WeissCara Carina; Catalina 36MkII,1995E. Greenwich, RI

 

[fred miller]

Vibration Cause

I don't know which model boat you own or engine, but on my 35.5 when I switched to a 3 blade prop from a 2 I noticed a couple of things. Obviously it is much smooother operating,less vibration etc etc but running inlets at 3000 RPM and when it is rough, there is a slight periodic vibration. My "expert" tells me it is from cavitation as the prop leaves the water and is more noticeable on a 3 blade than on a 2. I tried slowing the RPMs down per his recommendation and it seemed to solve it.Fred MillerM Squared

 

[Chick Weiss]

Problem Solved, I think

Thanks for your response, Fred. See what I say below (from another part of this website). I do believe I've found the difficulty and solution, yet I won't be confident for much more motoring.In a prior email and on the "ask all Catalina owners section," I reported a very bad, intermittent and unpredictable vibration and loud noise (at the time, my thinking was the cutlass bearing). I've had mechanics, trans people, divers, calls to Catalina and no solution over 2 seasons. I could never see where the problem was coming from when it happened and it could happen several times in one day or not for several weeks. Last week, I decided to call the prior owner who told me he had all these symptoms and frustrations and eventually saw the dripless seal cavitating. At a boat show he spoke to the seal's manufacurer who offered a 50 cent solution.I then called the manufacturer last week and received the same solution.Get 600 to 1000 grit wet/dry sandpaper. Cut a piece and fold in half so sandpaper is on outside. Pull back the bellows of the dripless seal and insert the paper and let the bellows return to its normal position. Then, rotate the paper around the shaft about 10 times(it will polish both the seal's stainless and carbon components)and this should solve the problem. Remove the paper. Some water will leak in during the sanding.Tomorrow I'm trying it. The former owner said it gave him a year of problem-free operation. The manufacturer said that the low speed version of the seal (for crafts under 12 mph; this is what is on a sailboat)may no longer be made. In its place a is the high speed version which has its own water feed (taken from cooling water from the engine). It is possible to adapt the low to the high speed version, I understand and I may do this in the fall. First, I'll see if the sanding works.Chick WeissC36MkII, #1394E. Greenwich, RI