Seahorse Marine Diesel Duck Vibration - Advice needed

[SeahorseMarineDD54201]

Regarding rubber isolation of the thrust bearing, look at the attached picture to see how Aquadrive isolates the thrust bearing from the bearing support structure.

You'll need rubber on both sides of the support structure to deal with reverse thrust.

Thank you ! If mechanical interface works out, I probably would just replace with an Aqua Drive

 

[dannc]

There is a magazine called Professional BoatBuilder that is a TREASURE trove of information. They used to sell the entire back collection for a few hundred dollars which I bought years ago and reference frequently.

Looks like they have put all of the back issues on line for FREE.

Professional BoatBuilder Back Issue Archive

Frankly, I would still spend the money for the zip file so I could store the issues myself. They might still sell the complete collection but I can't find it.

Here is a part of the index regarding vibration:

noise/vibration control: acoustic signatures, 46:50; analog/digital sound meter, 78:104; Barry Controls, 120:42; consultants, 34:27; Co-Rez, 120:42; diagnostics/computers, 5:48, 74:85; diesel-electric generator, 109:140; E-A-R bulletin, 26:54; engine mounts, 5:42, 34:22, 34:26, 34:27, 35:58, 120:38, 122:6; laminate thickness, 50:18; liquid sound-dampening products, 97:10; materials/methods, 5:42, 34:22, 34:26, 34:27, 34:59; minehunter ships, 65:84;
noise/vibration isolators, 34:59, 35:4; noise-cancellation headsets, 36:78, 78:104; noise-damping electronics/anti-noise systems, 46:50; noise isolation with thrust-bearing drivetrains, 120:42, 122:6; noise-reducing laminates, 32:4; QuietBoat viscoelastic polymer covering, 97:10; sources, 5:49, 34:27; turbo silencer/Navy specwar, 52:43; vibration severity chart, 74:85; waterjet propulsion systems, 67:70, 70:21. See also engines, marine, noise/vibration control; noise pollution; soundproofing insulation
noise/vibration isolators: Aquadrive, 35:4; ISOLOSS HD, 34:59; Silent Running SR 1000 viscoelastic coating, 147:10

There are other topics in the index that might help but this give a good idea of the information available.

The first number is the edition number and the second number is for the page. I am time constrained at the moment but issue 120 and 34 look to have articles that might help.

Later,
Dan

 

[twistedtree]

All these proposed solutions are based on guesses of what the actual vibration source/cause is. You can guess and try things until the problem goes away, or you can sort out ways to diagnose the source and fix it once in a way that works. Someone needs to measure the vibration, both in amplitude and frequency to determine the source.

 

[SeahorseMarineDD54201]

There is a magazine called Professional BoatBuilder that is a TREASURE trove of information. They used to sell the entire back collection for a few hundred dollars which I bought years ago and reference frequently.

Looks like they have put all of the back issues on line for FREE.

Professional BoatBuilder Back Issue Archive

Frankly, I would still spend the money for the zip file so I could store the issues myself. They might still sell the complete collection but I can't find it.

Here is a part of the index regarding vibration:
There are other topics in the index that might help but this give a good idea of the information available.

The first number is the edition number and the second number is for the page. I am time constrained at the moment but issue 120 and 34 look to have articles that might help.

Later,
Dan

Thank you ! Will read up. If you come across a zip file, let me know too !

 

[SeahorseMarineDD54201]

In reply #55 I said I left out another piece of clue: The factory installed whip bearing was found to be burnt, before it was replaced and moved a bit towards the aft (presently about mid way between Prop end Cutlass Bearing, and Thrust Bearing). The diagram below (attached in another earlier reply) has a note about this.

I was told by the yard the hose which feeds coolant to the bearing was clogged up by welding sooth, and that was the cause of the bearing being burnt. I accepted that because I did see black stuff in the transparent hose before boat delivery (in fact I wondered what it was and without proper explanation, I specifically asked Bill Kimley to check).

Now I think about it after all the discussion, and wonder if shaft whip could also be the cause.

 

[SeahorseMarineDD54201]

All these proposed solutions are based on guesses of what the actual vibration source/cause is. You can guess and try things until the problem goes away, or you can sort out ways to diagnose the source and fix it once in a way that works. Someone needs to measure the vibration, both in amplitude and frequency to determine the source.

Very expensive to get a professional vibration test done here. I was talking to an academia (see an earlier reply) who heads a vibration test research group. That is beginning to be expensive.

I did use Android vibration analysis app, tied up in a typhoon shelter and measured everywhere. Could not get any meaningful conclusion then. But now with the various things I can try, the frequency measurement might tell me much more.

 

[sean9c]

So how did you measure whatever tied up in a typhoon shelter? Is there a vibration with engine running but boat not moving?
Still unclear how your vibration analysis is going to be helpful. It will tell you that you have a vibration and a bunch of details about it but it won't tell you the cause.
IMO which is worth nothing, until you've worked through the mechanical issues to ensure shaft is supported correctly and that everything is aligned you're just throwing money away on your analysis.
Here is another thought. How much vibration is inevitable and are you being realistic with your expectations. As someone else also mentioned, that thrust bearing is hard mounted to a steel plate that's welded to your hull, every vibration from the prop/shaft is transferred right into the boat. The other thing is that the carden shaft is also connected to that hard mounted bearing, so noise from the engine and carden shaft are going into the hull. Your setup is not one designed to isolate vibration. Take a look at Aquadrive and the others, they not only take thrust but are isolated from the structure to reduce vibration.

Very expensive to get a professional vibration test done here. I was talking to an academia (see an earlier reply) who heads a vibration test research group. That is beginning to be expensive.

I did use Android vibration analysis app, tied up in a typhoon shelter and measured everywhere. Could not get any meaningful conclusion then. But now with the various things I can try, the frequency measurement might tell me much more.

 

[twistedtree]

So how did you measure whatever tied up in a typhoon shelter? Is there a vibration with engine running but boat not moving?
Still unclear how your vibration analysis is going to be helpful. It will tell you that you have a vibration and a bunch of details about it but it won't tell you the cause.
IMO which is worth nothing, until you've worked through the mechanical issues to ensure shaft is supported correctly and that everything is aligned you're just throwing money away on your analysis.
Here is another thought. How much vibration is inevitable and are you being realistic with your expectations. As someone else also mentioned, that thrust bearing is hard mounted to a steel plate that's welded to your hull, every vibration from the prop/shaft is transferred right into the boat. The other thing is that the carden shaft is also connected to that hard mounted bearing, so noise from the engine and carden shaft are going into the hull. Your setup is not one designed to isolate vibration. Take a look at Aquadrive and the others, they not only take thrust but are isolated from the structure to reduce vibration.

The frequency of the vibration can tell you quite a bit about the source. Does it match engine firing frequency (engine vibration)? Shaft speed (shaft whip or other misalignment)? Blades passing the hull? Blades passing through the keel shadow?


Also, if the vibration is along the shaft axis, that suggests the Cardan shaft or perhaps strength of the thrust bearing mount point. If it's radial to the shaft, then it's a balance, alignment, or other shaft flex/whip.


Because of the enclose shaft, there is very little ability to diagnose what's going on. Yes, experienced techs can identify frequently occurring problems/sources of vibration, but in the absence of any way to diagnose, they will just be guessing about the problem and fix.


The OP has already been through all the normal remedial steps; Prop balance, shaft straightness, cutlass bearings, U joints, etc. so it's a more complex problem, and he's now facing very expensive and complex fixes, none of which he has any reason to believe will fix the problem other than hope and prayer. I just think it's time for a little science since the usual guess and replace/fix hasn't solved the problem.


At this point I think the best clue is that everything runs smooth out of the water (no load), but not in the water (under load). That suggests there is a dynamic under load that is setting up some sort of vibration or harmonic. A dial gauge of the shaft would tell a lot, but can't be done given construction. A dial gauge on the thrust bearing could be interesting to see if it's pulsing fore and aft.

 

[Lou_tribal]

The frequency of the vibration can tell you quite a bit about the source. Does it match engine firing frequency (engine vibration)? Shaft speed (shaft whip or other misalignment)? Blades passing the hull? Blades passing through the keel shadow?


Also, if the vibration is along the shaft axis, that suggests the Cardan shaft or perhaps strength of the thrust bearing mount point. If it's radial to the shaft, then it's a balance, alignment, or other shaft flex/whip.


Because of the enclose shaft, there is very little ability to diagnose what's going on. Yes, experienced techs can identify frequently occurring problems/sources of vibration, but in the absence of any way to diagnose, they will just be guessing about the problem and fix.


The OP has already been through all the normal remedial steps; Prop balance, shaft straightness, cutlass bearings, U joints, etc. so it's a more complex problem, and he's now facing very expensive and complex fixes, none of which he has any reason to believe will fix the problem other than hope and prayer. I just think it's time for a little science since the usual guess and replace/fix hasn't solved the problem.


At this point I think the best clue is that everything runs smooth out of the water (no load), but not in the water (under load). That suggests there is a dynamic under load that is setting up some sort of vibration or harmonic. A dial gauge of the shaft would tell a lot, but can't be done given construction. A dial gauge on the thrust bearing could be interesting to see if it's pulsing fore and aft.

And may I risk the comment that and android app running on a phone is very far from a real analysis of the problem...

L

 

[D.Duck44]

Looking at the mounting of the thrust bearing. If I was setting that up, there would be substantial reinforcing members welded perpendicular to the plate which is supporting the bearing. Maybe there are some on the other side of the plate.
If not, you could bolt some heavy angle on to minimize any movement in that plate.

 

[Delfin]

I know it's not my vibration problem, and I know the OP feels the same way, but every forumite on this thread should be honored for your contribution to helping the OP's pretty significant problem get solved. Proud to be part of such a great community of folks who take other's problems as if they were their own.

 

[SeahorseMarineDD54201]

I am neither knowledgeable in boat nor a DIY type, but found myself in a situation I need to be one. Thanks to all the knowledge and experience shared with me. For continued help and as my way of appreciating all the help, I will share with the forum what I went through, and what I am going to do with very limited financial means.

The vibration measurement I did, is an example of having to do something when nothing could be done.

Back around late 2016, after two attempts at finding the problem (Whip Bearing found burnt, replaced, relocated towards aft, then Cardan Shaft/Engine/Shaft checked to be aligned under no load condition), Bill Kimley said he suspected the 3 blade Max Prop maybe the source vibration. He also said if it turns out not true, he would not know what to look for (though he was committed to fix the problem, even if he had to rebuild the whole drive train).

Therefore our next move was to replace the Max Prop, though Bill did not sound promising. Even though Seahorse had to pay the outrageous expense (yet normal and fair) at any Hong Kong yard, I wanted to do what I could to make it a productive yard visit. I was always courteous with Seahorse up to that time, trying to work with the yard to solve the problem.

Therefore I dreamed up the vibration measurement exercise which I could do on my own. I knew nothing about vibration measurement, except there are Android vibration analysis apps. Bill Kimley was very interested and supportive in the process (taught me how to tie the boat, etc.) and the results. However in the end neither of us knew enough on how to interpret the data. It probably was not collected properly in the first place by me anyway, and as pointed out in Post #67, the whole concept of vibration measurement may be questionable. If the boat could go back to Seahorse yard or a sub-contractor yard with minimal expense, I am sure that would have been the choice for both Seahorse and me, instead of me spending two days alone in a typhoon shelter.

Anyway here are some observations just for experience sharing, and feel free to ignore and not waste time:

1. Vibration was obvious without instrument measurement. However I thought the source of vibration power was ultimately the engine and transmission at 650-2500 rpm and 3:1 reduction. These are not the frequency human could feel (I believe), and I was hoping I could locate where else this RPM Correlated Frequency could be detected other than engine and transmission.

2. I placed the Android phone on Fly Bridge floor, forward and aft engine mounts, Gear Box, hull near Cardan Shaft (could not reach Thrust Bearing at the time), hull near Whip Bearing, hull near Propeller. I recorded the peak amplitude and corresponding frequency, cycling the rpm from 650 to 2500. I also did this with Transmission in neutral.

3. I quickly confirmed with transmission in neutral, there was no RPM Correlated Frequency detectable. It was point less to do more measurements in neutral (I was running up and down between Pilot House and Engine Room).

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.

As pointed out in #67 reply, ultimately something has to be done by fundamental engineering principles for the vibration to go away. Guessing the cause or measuring the vibration is all I can do when nothing else is done. However I am so grateful with so many comments, suggestions, and all knowledge shared. Especially some of the stuff can be done now (eg. checking shaft deflection near thrust bearing by scoring, strobe light, counter-pull) before returning to yard (but still need Seahorse' help).

 

[dannc]

I think we met SeahorseMarine54201 in China a few years ago and we saw his boat being built. It is a very nice boat and really frustrating/horrifying to have a problem like this.

I am busy busy busy with work and I am sleep and time deprived. I only mention this as an apology for not posting some thoughts sooner.

Earlier there was a post where Bill said that may the hull was panting. Possible I suppose, but the boat structure would be one of the last things I would spend much time checking.

Years ago I looked at Buehler's scantlings and ran Gerr's equations from "Elements of Boat Strength" against George's designs. I did not check everything but I looked at various hull structures and George's scantlings exceeded Gerr's equations from 25-35%. I did not check the engine bed structure though but I would be surprised if structure is the problem.

I have some of George's study planes for a variety of boats, including two 55 footers, and one around 50. The scantlings are the same on all three boats so if the 542 follows the other designs, it should be, as George would say, stout. Me thinks the problem is in the drive line...

Back to Professional Boat builder. Their website is not the best in the world but they have been very responsive to me by email and phone when I had a problem with the website and subscription issues. I would hope they still sell the zip file of back issues but I could not find it. All of the back issues seem to be online for free download though.

Later,
Dan

 

[SeahorseMarineDD54201]

I think we met SeahorseMarine54201 in China a few years ago and we saw his boat being built. It is a very nice boat and really frustrating/horrifying to have a problem like this.

I am busy busy busy with work and I am sleep and time deprived. I only mention this as an apology for not posting some thoughts sooner.

Earlier there was a post where Bill said that may the hull was panting. Possible I suppose, but the boat structure would be one of the last things I would spend much time checking.

Years ago I looked at Buehler's scantlings and ran Gerr's equations from "Elements of Boat Strength" against George's designs. I did not check everything but I looked at various hull structures and George's scantlings exceeded Gerr's equations from 25-35%. I did not check the engine bed structure though but I would be surprised if structure is the problem.

I have some of George's study planes for a variety of boats, including two 55 footers, and one around 50. The scantlings are the same on all three boats so if the 542 follows the other designs, it should be, as George would say, stout. Me thinks the problem is in the drive line...

Back to Professional Boat builder. Their website is not the best in the world but they have been very responsive to me by email and phone when I had a problem with the website and subscription issues. I would hope they still sell the zip file of back issues but I could not find it. All of the back issues seem to be online for free download though.

Later,
Dan

Good to hear from you Dan ! Yes I did meet you and your other half. I saw I believe, a thread started by you on this forum, talking about a visit of the yard, with some picture of DD54201. Those were good days for me.

Hope you have found the boat you want. George did tell me there is nothing on the hull to vibrate, in his opinion.

 

[SeahorseMarineDD54201]

At this point I think the best clue is that everything runs smooth out of the water (no load), but not in the water (under load).

Thanks for your kind comments and suggestions. Dial gauge was on my mind. I am also thinking about a laser or strobe light etc as suggested at various replies.

I need to correct your quote slightly as it has appeared twice.

The boat does not vibrate if there is no load, IN OR OUT OF WATER.

It does not vibrate in the water if left in neutral even at 2500rpm.

It did not vibrate in forward/reverse gear (at about 1200 rpm as far as I remember) when out of water (no load), and the prop turned very smoothly (as observed by a fellow DD462 Owner who is very knowledgeable)

 

[twistedtree]

Thanks for your kind comments and suggestions. Dial gauge was on my mind. I am also thinking about a laser or strobe light etc as suggested at various replies.

I need to correct your quote slightly as it has appeared twice.

The boat does not vibrate if there is no load, IN OR OUT OF WATER.

It does not vibrate in the water if left in neutral even at 2500rpm.

It did not vibrate in forward/reverse gear (at about 1200 rpm as far as I remember) when out of water (no load), and the prop turned very smoothly (as observed by a fellow DD462 Owner who is very knowledgeable)

Loading of the prop, which in turn loads the shaft, thrust bearing, engine, etc., is what I'm talking about. The dynamics will be totally and fundamentally different when the prop is pushing against water vs when the any of the drive line is spinning unloaded. What you have demonstrated is that the problem is loading related.


Under load, the prop blades will pound water against the hull with each pass. That will happen at engine RPM/60 divided by 3 (gear ratio) times 4 (number of blades). The shaft will be whipping at the shaft speed/frequency. And two opposing prop blades will pass through the keel shadow at the same frequency as the blades pounding water against the hull, but will cause and axial pounding on the shaft.

 

[SeahorseMarineDD54201]

Positive Development

I said in Post/Reply #6 that I was requesting Seahorse for funding a vibration measurement/analysis. In fact I thought in a later post I said the request went unanswered (but I cannot locate the text anymore). Regardless I am very happy Bill and Stella Kimley just replied today.

Bill and Stella Kimley asked me if I know any vibration analysis expert. Well ... I have to continue trying. As I said in post/reply #39 and #49, I talked to an academia who leads a practice in calibrated theoretical analysis, and I am having doubt whether that would apply in my case (I will discuss with Bill and let him decide). Recommended by a fellow boater in another boating forum with actual experience, I also asked a professional vibration analyst in USA, whether he would be interested in work in Hong Kong. That has not been answered. I am not sure when this path (vibration measurement) would lead to results, but I will keep trying.

Bill and Stella Kimley also said they could have the shaft replaced with a higher quality in Hong Kong. Bill cautioned me this may or may not solve the problem.

In that regard I believe Seahorse needs to set aside a huge budget for trial and error exercises in a Hong Kong yard (the shaft material is just an appetizer). I actually have no expectation (therefore need not be cautioned against) after 4 Seahorse attempts, that the problem would be solved with one single sub-contractor yard visit. It would eliminate some guesses though.

In replacing the shaft I will again work with Seahorse, to make the next yard visit productive. Seahorse can learn from the pool of knowledge and good will of the community. I will refer Bill Kimley to all the suggestions and tips offered from the boating community (especially Trawler Forum) that so much more can be confirmed before the very expensive yard visit. In addition I will do my utmost to support any investigation activities in Hong Kong (spending days in typhoon shelter, looking after Seahorse workers etc.), before the boat goes to the yard.

I look forward to this. I will keep all updated on the progress, especially how well those troubleshooting tips work, with Seahorse' help.

Bill also stated under the current government policy (towage and bond), Seahorse cannot afford the expense to bring my boat back into the Seahorse yard.

 

[SeahorseMarineDD54201]

Loading of the prop, which in turn loads the shaft, thrust bearing, engine, etc., is what I'm talking about. The dynamics will be totally and fundamentally different when the prop is pushing against water vs when the any of the drive line is spinning unloaded. What you have demonstrated is that the problem is loading related.


Under load, the prop blades will pound water against the hull with each pass. That will happen at engine RPM/60 divided by 3 (gear ratio) times 4 (number of blades). The shaft will be whipping at the shaft speed/frequency. And two opposing prop blades will pass through the keel shadow at the same frequency as the blades pounding water against the hull, but will cause and axial pounding on the shaft.

I think we both understand the vibration is loading related. I just want to point out the boat does not vibrate in water either, if gear in neutral.

First time I get some insight on prop blade/hull interaction. Thanks, and I will spend some time to think about it.

 

[D.Duck44]

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.

 

[Steve DAntonio]

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-content/uploads/2014/03/Shaft-Alignment-159-02.pdf

 

[ctsbillc]

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.

 

[SeahorseMarineDD54201]

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.

 

[SeahorseMarineDD54201]

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-content/uploads/2014/03/Shaft-Alignment-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.

 

[diver dave]

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.

 

[D.Duck44]

Our Duck has an Aquadrive but have not yet given it a run to check on vibration. Will report back when we do.

 

[psneeld]

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. "!

 

[healhustler]

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.

 

[Destiny]

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.

 

[Kit_L]

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).

 

[Steve DAntonio]

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?