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Old 06-15-2018, 04:18 PM   #81
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Envious of your ride. Nice boat.
Speaking as an engineer, and an electrical one at that (I stand ready to be corrected by a mech eng), seems you have a resonance, and it's due to physical characteristics like lengths and masses. As to what is resonating and how it's being excited, I don't know, but your solution is to find out, and dampen whatever it is. When energy is going into a vibratory system, it builds up until loss equals the energy going in, and the trick is to get that energy out fast to stop it from building up. The old rod to ear trick may help locating where it is worse. Hard rubber pads between surfaces may help damp it when you've found where the antinode, the bit which moves most, is located.
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Old 06-15-2018, 05:44 PM   #82
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Another thought - your splined cardan shaft will tend to resist sliding in an out under load, unlike a CV joint which transmits load through balls.
I wonder whether it may be worthwhile replacing it with an Aquadrive unit? In the scheme of things not too expensive, and a better unit anyway.
Yes, In earlier post/reply, there were some concern and discussion on "telescopic" Cardan Shafts, and I am satisfied these should be ok in design, and these are installed in all other DD462s in practice.

Having said that I always looked at mine with some suspicion. I said in another post I suspect and will check for "play" with the two halves of the shaft to be exactly in phase.

Now thinking about your comments, I would probably use a strobe light to check for the amount of slide. I am beginning to learn from this forum !

I will ask Seahorse to send me an identical Cardan shaft to swap for try out. If that turns out to be the culprit, I'll return my original.
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Old 06-15-2018, 05:54 PM   #83
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I'm sorry to hear about the issues with Bill and Stella. I've been to this yard and must say it's among the most interesting I've ever visited, if for no other reason than Bill's train set.

Seems obvious, and perhaps already mentioned, but has the shaft been checked for straightness? And, has it been confirmed that the shaft coupling bore is centered, and that the coupling pilot bushing is centered in the recess in the coupling with which it mates? Is the shaft tapered at the coupling end? Ideally it should be.

I have had experience with locally made couplings in Asia on several occasions not being on center. All of these issues can be easily identified using a dial indicator. To fully and properly check shaft straightness it would need to be pulled from the vessel, however, determining if the shaft is centered in the coupling or if the coupling pilot is correct could be done without shaft removal.

It's also worth noting that misalignment, because it is constant, rarely causes vibration. Eccentrics in running gear lead to vibration.

I've also had something as simple as a defective, new motor mount cause serious vibration. The list of possibilities, especially with a system that has some unusual features, is nearly endless. You need professional support or you could chase this endlessly. I've contracted with vibration analysts who, in a few hours, can literally point to the offending source.

The outfit I profiled in this article is among the best in the business when it comes to vibration analysis, and repair (they are in South Florida). They may be willing to consult for you, from afar. Otherwise, a known marine vibration analyst in the HK area may be your best bet.
http://stevedmarineconsulting.com/wp...ent-159-02.pdf
Yes, as mentioned in a few earlier Posts/Replies, the shaft was pulled out (ie. no load) and checked for straightness.

Not sure what you mean by (propeller) shaft coupling bore and pilot bushing. But the shaft is tapered, and locked with a key to a flange, which is bolted to the flange on the Cardan Shaft. Attached is the diagram of the shaft. The right hand side of the shaft connects to the Cardan shaft.

As mentioned in earlier Post/Reply, the propeller and engine were run together out of water (lubrication to bearings maintained), and the propeller turned smoothly, which to me, means the shaft was aligned and centered if there is no load.

I saw on Youtube of someone checking for shaft deflection with a dial gauge, with the shaft turning ! I think I'll try that. I am also thinking of using a laser which should bounce off as a line if there is any deflection. I am getting a lot of help and suggestions from everyone in this thread and I am grateful.

As mentioned in an earlier Post/Reply, Bill Kimley replied to my email and asked me to find a vibration specialist. I will certainly tell him about this guy from South Florida. Remote consulting might work. Thank you ! I asked around in Hong Kong. I think there is one, but extremely expensive.

Yes, Bill Kimley is a special kind of guy. Did you hear his joke about the optional stray dog that comes with every boat, you pay for the option of not getting one ? That used to be funny until I realized the dog I got is named Vibra.
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Old 06-15-2018, 06:21 PM   #84
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I have not done a ton of marine shaft work, but done some other vib analysis. There is a Fluke model 805 handheld vibration meter that I have used in the field. Very easy to get measurements. Also, you did a topside run with wheel on. I was thinking a wet run with NO wheel on, thru all RPM's would be telling. In water, the hull will rest at the "normal" position. Running with no prop should be very smooth, of course that does not result on any compressive loading of the shaft. So, if its shaking there, you know there is a power train issue.
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Old 06-15-2018, 06:29 PM   #85
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Our Duck has an Aquadrive but have not yet given it a run to check on vibration. Will report back when we do.
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Old 06-15-2018, 06:55 PM   #86
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From a professional marine engineer friend....

"Having used professional vibration analysis firms over the years to diagnose problems like the OP presented, I can say with no reservations that chasing vibration issues by doing anything else in 2018 is truly a fool's errand. "!
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Old 06-15-2018, 08:36 PM   #87
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Such great feedback above. Regarding vibes only under load, let me interject one other possibility that I haven’t seen mentioned (apologies if I missed it). A decently balanced prop would spin exactly as you reported in the dry test, but under load in water, even a perfectly balanced prop would wobble if one of the three blades were not pitched as the other two. You already know that the bite of blades on the top stroke are moving through water of less density than the two that are moving in and out of their lower strokes. Add a bit less pitch on one blade and you’ve got a pretty strong encouragement for the shaft (especially if undersized or compromised in material) to bow up and down with each revolution, and getting worse as RPM’s (load) increased. Thanks to a well placed and sturdy cutlass, any resulting bow would likely occur between the cutlass and the next bearing, likely inside the shaft log itself. This, just to add to your considerations.
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Old 06-16-2018, 02:14 AM   #88
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I've just caught up with this thread and my sympathies to the OP. For what it's worth:-
We have a smaller Duck (DD44) that for years had noise and vibration, though not severe. In the end I dumped the Carden drive and replaced it with a stub drive shaft and an aquadrive unit. In checking we found that the prop shaft flange was not centred and had worn the shaft bearing - both were replaced. Finally we found that the rudder bearing was worn and creating it's own rumble, that had been thought to be a transmission noise - that was replaced. Finally peace. Now we have a smooth operating piece of machinery. Good luck with your engineering.
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Old 06-16-2018, 06:32 AM   #89
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Joining this thread simply to see how this turns out, and hoping for a speedy and not-too-expensive resolution!

To Steve D’Antonio: thanks for an enlightening article (the PDF linked to).
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Old 06-16-2018, 08:13 AM   #90
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Originally Posted by SeahorseMarineDD54201 View Post
Yes, as mentioned in a few earlier Posts/Replies, the shaft was pulled out (ie. no load) and checked for straightness.

Not sure what you mean by (propeller) shaft coupling bore and pilot bushing. But the shaft is tapered, and locked with a key to a flange, which is bolted to the flange on the Cardan Shaft. Attached is the diagram of the shaft. The right hand side of the shaft connects to the Cardan shaft.

As mentioned in earlier Post/Reply, the propeller and engine were run together out of water (lubrication to bearings maintained), and the propeller turned smoothly, which to me, means the shaft was aligned and centered if there is no load.

I saw on Youtube of someone checking for shaft deflection with a dial gauge, with the shaft turning ! I think I'll try that. I am also thinking of using a laser which should bounce off as a line if there is any deflection. I am getting a lot of help and suggestions from everyone in this thread and I am grateful.

As mentioned in an earlier Post/Reply, Bill Kimley replied to my email and asked me to find a vibration specialist. I will certainly tell him about this guy from South Florida. Remote consulting might work. Thank you ! I asked around in Hong Kong. I think there is one, but extremely expensive.

Yes, Bill Kimley is a special kind of guy. Did you hear his joke about the optional stray dog that comes with every boat, you pay for the option of not getting one ? That used to be funny until I realized the dog I got is named Vibra.
For a variety of reasons, running the engine and shaft out of the water really isn't a valid analysis. A dial indicator on the shaft at the coupling initially, will be a very valuable test. The shaft is turned slowly by hand, ideally with the boat afloat.

The first photo, of a coupling, in this article The Ins and Outs of Engine and Shaft Alignment Part I | Steve D'Antonio Marine Consulting with the laser in the middle, shows the pilot pushing on the transmission flange (it's damaged). It interfaces with a recess on the shaft coupling. If these are not centered, you will have vibration.

The bore or hole in the shaft coupling must, for obvious reasons, be centered in the coupling, as must the pilot bushing. If not, the shaft rotation will not be smooth, it will revolve about an axis rather than rotate on it.

Once again, a professional analyzing the vibration, preferably onsite but remotely if necessary, will be money well-spent.

I did hear Bill's stray dog joke;-) BTW, there's a photo of a DD under construction in this article, it was taken in 2015. A Boat Buyer’s ‘Top Ten’ Guide to a Pre-Offer Evaluation Part I | Steve D'Antonio Marine Consulting During that yard visit the vessels I reviewed had conventional, double universal joint shafts and thrust bearings, shown here. Is yours not like this?
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Old 06-16-2018, 11:40 AM   #91
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Professional Boat Builder issue number 74, page 85, has an article about vibration which is pretty good. The article is from 2002 and most of the company websites listed at the end of the article are no longer valid, one website is still available, http://www.balmacinc.com/products/digital-vibration-meters#spucontent205

This company sells devices but not sure how much they cost. But they do have some interesting information on the FAQ page, FAQs, that has some helpful documents, including a chart that talks about how to interpret the test results,http://www.balmacinc.com/downloads/SeverityChart.pdf.

Not sure it is worth the OP buying one of the devices but some of this information might be helpful to know when hiring someone. The company might have some contacts in HK as well.

The article mentions using vibration sensors to equipment that might help detect vibration before they become an issue or out right failure. Interesting idea.

Later,
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Old 06-16-2018, 02:34 PM   #92
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When I looked at the graph in Post 72 of this thread I was reminded of two very dramatic structure vibration problems from my experience in industry (not boats or marine). Both of these problems resulted from very small oscillating forces being applied to a structure at, or close to a natural vibration frequency of the structure. To understand the problem required identifying the source of the small oscillating force, and the natural frequencies of the structure.

What caught my eye in the graph in Post 72:

A. The dominant vibration frequency at the engine mount and the thrust bearing in the two rpm ranges where the vibration is most prominent are generally the same, and at the engine rpm frequency. (one exception, all data seems to have to do that to keep us humble) If the oscillating force was due to misalignment of the shafts, eccentricity of the couplings, bent shaft, or whip due to one of these things the thrust bearing dominant frequency should be 1/3 the engine speed. The gear ratio is 3:1 and the prop has three blades, so this means any oscillating force produced by the relationship with the prop and the hull or deadwood would be at engine speed. All of this leads me to tend towards the engine or the hydrodynamic interference between the prop blades and the hull or deadwood as the source of the oscillating force. I also note from the facts presented that the prop is one of a few unique elements of this installation.

B. The sympathetic vibration caused by the application of an oscillating force to a structure can happen if the natural frequency is a multiple of the frequency of the force. It appears from the graph that the higher frequency where the force and natural frequency may be aligned are about double the lower, with the higher being just above the maximum rpm of the engine. This would help to confirm that the issue is not just the magnitude of the oscillating force, but also the natural frequency of the structure it is applied to. This is valuable to know as it gives you two ways to mitigate the effect, reducing the force, or changing the natural frequency of the structure.

An amateur in an armchair half way around the world from the problem has no chance of solving it, but with that qualifier here’s my input.

I suspect that the source of the oscillating force is the propeller, with the oscillation caused by the interaction between blades and hull or deadwood. I believe the second propeller tried was also a 3 blade, so would have changed the forces, but not the frequency. If the source was the engine the structure would not be absolutely smooth in neutral.

I suspect that the structural element with the troublesome natural frequency is the reinforced plate diaphragm welded to the engine beds that the thrust bearing is bolted to. It could also be the unsupported shaft, but moving the center bearing should have made some difference if that were the case.

The two things I would try first to mitigate the problem:
Add some rubber washers on both sides of the plate where the thrust bearing is bolted. Several have suggested this. The goal here is to reduce the oscillating force.
Weld some angle iron braces between the engine bed and the diaphragm plate as close as possible to the thrust bearing, transferring the axial force on the diaphragm directly to the engine bed stringers. Stiffening this plate has also been suggested by others. The goal here is to change the natural frequency.

So says the armchair amateur on the other side of the world. I agree that a competent structural vibration analysis with current analytical tools would have a high probability of success!

I think the OP was on the right track with his questions below in post 72.

Bill


“4. The graph below show dominant vibration frequency measured below engine mount and below thrust bearing (a lot more data available for those interested) . I added some notes which are extracted from the starting post of this whole thread. These describe the "subjective" vibration sensation I felt, and there seems to be some kind of correlation that if engine rpm is transmitted through engine mount and to thrust bearing, I would sense the vibration. But isn't that obvious, that the power that drives the vibration has to come from the engine. But interestingly is:



5. Why engine frequency was not transmitted to below thrust bearing at the quiet range (per my subjective sense) ? Was there some kind of "destructive interference" to counter against engine power ? Anyway I am not to ask anyone for an answer, but just a question in my mind.”
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Old 06-16-2018, 06:16 PM   #93
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I have not done a ton of marine shaft work, but done some other vib analysis. There is a Fluke model 805 handheld vibration meter that I have used in the field. Very easy to get measurements. Also, you did a topside run with wheel on. I was thinking a wet run with NO wheel on, thru all RPM's would be telling. In water, the hull will rest at the "normal" position. Running with no prop should be very smooth, of course that does not result on any compressive loading of the shaft. So, if its shaking there, you know there is a power train issue.
I will look into the Fluke meter, though I doubt I can afford one, nor would it help much in the wrong (my) hand. Bill Kimley did ask me to look into hiring a professional, who would bring his/her own equipment.

I took the measurement with an Android phone while tied up in the water in an empty typhoon shelter.

I don't understand what you mean by "top side run with wheel on", "wet run with no wheel on". Could you elaborate ?
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Old 06-16-2018, 06:27 PM   #94
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From a professional marine engineer friend....

"Having used professional vibration analysis firms over the years to diagnose problems like the OP presented, I can say with no reservations that chasing vibration issues by doing anything else in 2018 is truly a fool's errand. "!
Thank you for your comment.

I need to understand the concept of the appropriate vibration analysis which would apply to my boat.

As stated in earlier Posts/Replies, I am aware of an approach which I call "Calibrated Theoretical Model". Torsional vibration at various points of the drive train is predicted through a theoretical model. Then a sensor is placed (I was told only one sensor needed) near the engine end of the shaft, and the measured result is used to calibrate the theoretical model to identify the source of vibration. Then more sensor(s) can be used to confirm the source.

I feel this approach is more of a tool to eliminate resonance at design/construction stage. I would think in my already built boat, the measurement should not rely on a theoretical model.

Would you share some of your thoughts/experience on vibration measurement by professional boat vibration trouble shooter ? Can you recommend one as well ? I need to share this with Bill Kimley.
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Old 06-16-2018, 06:35 PM   #95
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Such great feedback above. Regarding vibes only under load, let me interject one other possibility that I haven’t seen mentioned (apologies if I missed it). A decently balanced prop would spin exactly as you reported in the dry test, but under load in water, even a perfectly balanced prop would wobble if one of the three blades were not pitched as the other two. You already know that the bite of blades on the top stroke are moving through water of less density than the two that are moving in and out of their lower strokes. Add a bit less pitch on one blade and you’ve got a pretty strong encouragement for the shaft (especially if undersized or compromised in material) to bow up and down with each revolution, and getting worse as RPM’s (load) increased. Thanks to a well placed and sturdy cutlass, any resulting bow would likely occur between the cutlass and the next bearing, likely inside the shaft log itself. This, just to add to your considerations.
I am getting a free lesson here. If I am a smart student (and I am not), amd I correct I would start looking at the shaft ...

On the other hand as stated in an earlier Post/Reply, in the very last (4th) attempt, the Hong Kong Sub-Contractor did insert Whip Bearing No. 2 from the aft, which got stuck about 2 ft from the Cutlass Bearing. Though Bearing No. 2 should not have been inserted as I realize now, it was there as an additional force to constrain the shaft against the force you mentioned above. In your opinion what would happen ?
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Old 06-16-2018, 06:49 PM   #96
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I've just caught up with this thread and my sympathies to the OP. For what it's worth:-
We have a smaller Duck (DD44) that for years had noise and vibration, though not severe. In the end I dumped the Carden drive and replaced it with a stub drive shaft and an aquadrive unit. In checking we found that the prop shaft flange was not centred and had worn the shaft bearing - both were replaced. Finally we found that the rudder bearing was worn and creating it's own rumble, that had been thought to be a transmission noise - that was replaced. Finally peace. Now we have a smooth operating piece of machinery. Good luck with your engineering.
Thank you for sharing your experience. I believe Destiny is an earlier duck built by Seahorse. Are you the original owner ?

Doing away with Cardan shaft seems to be a drastic (and risky) move. I know two DD462 owners did that because the shafts was corroded and in North America, boat yards are more familiar (therefore less risky) with direct shaft/transmission coupling.

In your case what led to the decision to remove Cardan shaft ? To solve the vibration problem by changing configuration, or the need to follow local approach in shaft replacement ?

Also if you don't mind so I can have a reference, what is your engine power, original shaft length, shaft diameter ? How far is the whip bearing from the thrust bearing ?

Thank you in advance.
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Old 06-16-2018, 07:01 PM   #97
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For a variety of reasons, running the engine and shaft out of the water really isn't a valid analysis. A dial indicator on the shaft at the coupling initially, will be a very valuable test. The shaft is turned slowly by hand, ideally with the boat afloat.

The first photo, of a coupling, in this article The Ins and Outs of Engine and Shaft Alignment Part I | Steve D'Antonio Marine Consulting with the laser in the middle, shows the pilot pushing on the transmission flange (it's damaged). It interfaces with a recess on the shaft coupling. If these are not centered, you will have vibration.

The bore or hole in the shaft coupling must, for obvious reasons, be centered in the coupling, as must the pilot bushing. If not, the shaft rotation will not be smooth, it will revolve about an axis rather than rotate on it.

Once again, a professional analyzing the vibration, preferably onsite but remotely if necessary, will be money well-spent.

I did hear Bill's stray dog joke;-) BTW, there's a photo of a DD under construction in this article, it was taken in 2015. A Boat Buyer’s ‘Top Ten’ Guide to a Pre-Offer Evaluation Part I | Steve D'Antonio Marine Consulting During that yard visit the vessels I reviewed had conventional, double universal joint shafts and thrust bearings, shown here. Is yours not like this?
Thank you for your reply. I will look at the picture in the article and see if/how my boat has any similar issues.

Yes the Cardan Shaft in your picture is what I have, though mine looks a bit tattered out as delivered. As stated in another Post/Reply, I plan to re-check for correct phasing, the play between the spline, and the linear slide between the two halvess
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Old 06-17-2018, 01:47 AM   #98
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Originally Posted by SeahorseMarineDD54201 View Post
Thank you for sharing your experience. I believe Destiny is an earlier duck built by Seahorse. Are you the original owner ?

Doing away with Cardan shaft seems to be a drastic (and risky) move. I know two DD462 owners did that because the shafts was corroded and in North America, boat yards are more familiar (therefore less risky) with direct shaft/transmission coupling.

In your case what led to the decision to remove Cardan shaft ? To solve the vibration problem by changing configuration, or the need to follow local approach in shaft replacement ?

Also if you don't mind so I can have a reference, what is your engine power, original shaft length, shaft diameter ? How far is the whip bearing from the thrust bearing ?

Thank you in advance.
We took professional advice from a company in Malta who are more experienced in big yachts and ships than I am in terms of transmissions.
My own feeling was that the Carden drive looked like it had come off of an old Chinese truck and because this was an early model duck, somebody had decided to add it in. Incidentally (we are 2nd owners - looking for a 3rd) I did find in the 'parts' box a direct coupling shaft that seemed to suggest that originally the shaft was direct coupled to the gearbox.

The original Carden was worn on one of the bearings and we'd earlier replaced it with another which hadn't helped. My own feeling was that the Carden was a lot of metal on metal which is only going to increase/ amplify any noise or rumble in the sytem.

Tech info: Engine is JD 120HP 4Cyl, The is no intermediate/ whip bearing, shaft length - not sure I'd guess about 3.5M (10ft) 1 3/4" dia. For extra info we dropped the shaft a few years back, to change the cutlass bearing, check for shaft alignment and check prop balance.
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Old 06-17-2018, 05:06 AM   #99
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When I looked at the graph in Post 72 of this thread I was reminded of two very dramatic structure vibration problems from my experience in industry (not boats or marine). Both of these problems resulted from very small oscillating forces being applied to a structure at, or close to a natural vibration frequency of the structure. To understand the problem required identifying the source of the small oscillating force, and the natural frequencies of the structure.

What caught my eye in the graph in Post 72:

....................
Thank you so much for taking the time, and for your suggestions. It would take me a lot of time to think through, but perhaps the corrective actions could be tried before I understand the analysis.

For your interest, and since it is so easy to generate graphs, all the dominant frequency data is graphed below, ONLY FOR THE CURIOUS. OTHERS PLEASE DO NOT WASTE YOUR TIME. For the sake of standardizing the language, I define vibration frequency ranges according to my SUBJECTIVE sense in four:

1. Start Up Zone (from 650rpm to Approx 1100/1200rpm) where vibration increases with rpm, but could be considered as "normal".

2. Vibration Zone (from 1100/1200rpm to about 1700/1800rpm) where vibration ramps up and has a peak at about 1500rpm. Everything rattle and the floor on fly bridge jumps

3. Damped Zone (from 1700/1800rpm to 2100/2200rpm) where vibration intensity reduces to something like 1200/1300rpm

4. Beat Zone (from 2100/2200rpm and upward, engine max out at 2500rpm) where the vibration intensity goes up and down regularly everyone few seconds, and worse than Vibration Zone.

There is still the maximum intensity data I may or may not even know how to graph. The Android App I used only measure maximum intensity and corresponding frequency. I just found one which generates the whole frequency spectrum and intensity at the same time. Hmmm... I dread going to that typhoon shelter in the middle of nowhere ...

All this said, I want to acknowledge some previous Posts/Replies, that an Android is not a real vibration detector, the whole concept of vibration measurement is not understood by me, that fundamental trouble shooting principles and actual fixes are still the most important.
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SeahorseMarineDD54201 is offline   Reply With Quote
Old 06-17-2018, 08:03 AM   #100
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City: ACIW
Country: USA
Vessel Name: Freedom
Vessel Model: Albin 40
Join Date: Oct 2011
Posts: 19,117
Some suggestions passed to me from a tech savy friend.....

" Advanced Mechanical Enterprises Rich Merhige was my go to guy when I was technical superintendent for Camper & Nicholsons. I have also worked with Chris at High Seas for shaft and rudder bearing work but vibration analysis is not his forte'. Vibration analysis is like a medical specialist, all doctors have a basic MD but you don't go to a knee surgeon for a heart problem.

I find it incredible that so many people are tossing in suggestions to buy this or that piece of instrumentation or rubber washers or some other means to throw good money away chasing ghosts. I guess if the OP wants to make a hobby out of amateur vibration sleuthing he could follow the advice of the many but if he wants to cure the problem there is only one way to do it quickly and economically.

Considering the builder and location and the way those folks work it probably is a kluge of bad workmanship, misalignment, and wrong parts but like most marine engineering problems, just throwing parts at it will probably be very expensive and equally frustrating. "
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