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Old 06-12-2018, 09:46 AM   #41
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Sorry if this idea has already been floated by others, or if I have missed some important detail, but for what it's worth....

You mentioned that out of the water, there is no vibration but in the water there is. That would be what you would expect if the force of the water is causing the shaft to whip in response to the differential pressure of water exerted on the prop near the hull or away from it. You might be able to visually observe if this is a valid concept by carefully marking the shaft right at the flange bearing or on the cardan shaft where shown with a very fine scoring at the dock and then seeing if the shaft is pumping under power, as I suspect it may be due to the long unsupported length within the stern tube. The amount of movement may be too small to detect, so this may not work, but it would be free to try.

If this is what is going on, a cort nozzzle would likely solve the problem, but a larger diameter shaft may be the only permanent solution.
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Old 06-12-2018, 11:58 AM   #42
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If the whip is large enough to be visible, a strobe light synchronized to the shaft rpm would show it. If the sync is slightly out or the phase angle adjusted, you would see the shaft appear to move. You may be able to use an ignition strobe triggered by the tach signal from the alternator.

If the shaft is marginally stiff, you may not need to go all the way to 2.5". The 4th moment of 2" is 0.785 in^4, 2.25 is 1.258 in^4, already 60% stiffer. 2.5" is 1.917 in^4, over twice as stiff.
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Old 06-12-2018, 12:03 PM   #43
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Originally Posted by DDW View Post
If the whip is large enough to be visible, a strobe light synchronized to the shaft rpm would show it. If the sync is slightly out or the phase angle adjusted, you would see the shaft appear to move. You may be able to use an ignition strobe triggered by the tach signal from the alternator.

If the shaft is marginally stiff, you may not need to go all the way to 2.5". The 4th moment of 2" is 0.785 in^4, 2.25 is 1.258 in^4, already 60% stiffer. 2.5" is 1.917 in^4, over twice as stiff.
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Old 06-12-2018, 01:34 PM   #44
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So you're going to hire an egghead to do a bunch of analysis. Then what? He's going to tell you you have a vibration and probably give you a bunch of fancy data about your vibration, likely he won't be able to tell you how to fix it.
I think you'd be better off finding a naval architect or someone that knows their stuff, that can look at what you have, determine if the design and materials are correct and one that understands the correct process for aligning your shaft.
The 2 big things that I think are going to cause the most head scratching are, is the shaft a decent alloy and usable or crap and needs to be replaced and if that flange bearing is adequate as your thrust bearing, it is really a cheap set up..
As I've said before the alignment part isn't complicated, you just need to know what you're trying to accomplish and then work through the steps.
After saying all that I realize that this is all the stuff you'd need to do before having your vibrational academic come out and do an analysis. Why bother with an analysis before you know you've done everything possibly to have the mechanical components correct.

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Originally Posted by SeahorseMarineDD54201 View Post
Thanks for all the suggestions. The boat is in Hong Kong and going into a yard alone is extremely expensive. I now have some ideas what I can experiment with on my own, and what should be done in the yard, based on all the suggestions. I hope a vibration measurement/analysis would help, if affordable.

I am talking to an academia who leads in boat vibration research. I understand the following:

1. There are three types of vibration. One usually start with "torsional vibration" measurement, and for a boat small like mine, that's where it usually stop.

2. They start by a theoretical calculation of torsional vibration at various drive train components of the boat, based on characteristics and parameters of drive train equipment and boat structure.

3. Then they place one vibration sensor, drive the boat in a straight line for something like half hour. Based on what is measured, they re-evaluate the model (ie. something like a calibration process), and they can precisely determine/calculate the actual amount of vibration at various point/equipment on the boat.

4. Then they can place the sensor on the suspect location/equipment to confirm.

I need to spend sometime negotiate for a price I can afford. I probably have to start another thread to keep all updated on what happens.

I tried to attach a picture of the Caden Shaft in another reply and failed. Here is another try:
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Old 06-12-2018, 03:49 PM   #45
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If you're docked, you could double up the lines and do a bollard pull rather than running for a half hour in a straight line. In a past project, we did a vibration analysis and they used 3-4 pucks placed around the gear and could triangulate the source of the different vibrations based on frequency.
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Old 06-12-2018, 04:14 PM   #46
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Originally Posted by sean9c View Post
So you're going to hire an egghead to do a bunch of analysis. Then what? He's going to tell you you have a vibration and probably give you a bunch of fancy data about your vibration, likely he won't be able to tell you how to fix it.
I think you'd be better off finding a naval architect or someone that knows their stuff, that can look at what you have, determine if the design and materials are correct and one that understands the correct process for aligning your shaft.
The 2 big things that I think are going to cause the most head scratching are, is the shaft a decent alloy and usable or crap and needs to be replaced and if that flange bearing is adequate as your thrust bearing, it is really a cheap set up..
As I've said before the alignment part isn't complicated, you just need to know what you're trying to accomplish and then work through the steps.
After saying all that I realize that this is all the stuff you'd need to do before having your vibrational academic come out and do an analysis. Why bother with an analysis before you know you've done everything possibly to have the mechanical components correct.
For my info, what makes you think this is cheap setup?

L
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Old 06-12-2018, 07:29 PM   #47
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Originally Posted by Delfin View Post
Sorry if this idea has already been floated by others, or if I have missed some important detail, but for what it's worth....

You mentioned that out of the water, there is no vibration but in the water there is. That would be what you would expect if the force of the water is causing the shaft to whip in response to the differential pressure of water exerted on the prop near the hull or away from it. You might be able to visually observe if this is a valid concept by carefully marking the shaft right at the flange bearing or on the cardan shaft where shown with a very fine scoring at the dock and then seeing if the shaft is pumping under power, as I suspect it may be due to the long unsupported length within the stern tube. The amount of movement may be too small to detect, so this may not work, but it would be free to try.

If this is what is going on, a cort nozzzle would likely solve the problem, but a larger diameter shaft may be the only permanent solution.
Thanks for the suggestions which gave me ideas on what to look for.

I need to do an assessment of the worst case, that I need to replace the shaft with a bigger one.

Here in this part of the world, everyone says a yard would ream the existing fiberglass stern tube, which seem to me to be very precise therefore costly.

I am thinking why not used a pipe, cut some teeth, using the transmission flange to center, then just rough drill the entire stern tube (and surrounding epoxy filling between tube and steel shaft log), and re-epoxy a larger stern tube.

Anyone has seen my "dreamed up" approach in practice by experienced yards in USA ?
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Old 06-12-2018, 07:34 PM   #48
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Quote:
Originally Posted by DDW View Post
If the whip is large enough to be visible, a strobe light synchronized to the shaft rpm would show it. If the sync is slightly out or the phase angle adjusted, you would see the shaft appear to move. You may be able to use an ignition strobe triggered by the tach signal from the alternator.

If the shaft is marginally stiff, you may not need to go all the way to 2.5". The 4th moment of 2" is 0.785 in^4, 2.25 is 1.258 in^4, already 60% stiffer. 2.5" is 1.917 in^4, over twice as stiff.
Thanks for the info and suggestion. I have more to work with.

If indeed 2.25" shaft is enough, I could get away with using the existing stern tube, by precision ream to enlarge the two ends (about 3.3 meters apart). But according to the 40X guideline recommended by shaft manufacturer, the shaft would be under-supported.
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Old 06-12-2018, 07:59 PM   #49
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Originally Posted by sean9c View Post
So you're going to hire an egghead to do a bunch of analysis. Then what? He's going to tell you you have a vibration and probably give you a bunch of fancy data about your vibration, likely he won't be able to tell you how to fix it.
I think you'd be better off finding a naval architect or someone that knows their stuff, that can look at what you have, determine if the design and materials are correct and one that understands the correct process for aligning your shaft.
The 2 big things that I think are going to cause the most head scratching are, is the shaft a decent alloy and usable or crap and needs to be replaced and if that flange bearing is adequate as your thrust bearing, it is really a cheap set up..
As I've said before the alignment part isn't complicated, you just need to know what you're trying to accomplish and then work through the steps.
After saying all that I realize that this is all the stuff you'd need to do before having your vibrational academic come out and do an analysis. Why bother with an analysis before you know you've done everything possibly to have the mechanical components correct.
The academia I talked to does commercial work for boat/ship industry, so there is some credibility. On the other hand His approach is a theoretical one with actual measurement for calibration. It seems more like a design tool to prevent resonance, while mine is a built boat and resonance is one among many possible causes.

In contrary, I imagined such measurement would be more direct (e.g. "triangulation" as mentioned by another feedback post). In another forum there are comments, that done by the right people and equipment, the measurement these days are much more accurate and does not even have to be expensive. So I am still checking around to find the "right people and equipment".

Having said that I agree with you to go ahead and check everything possible, and I am grateful with some many ideas and suggestions on this thread. I am also in contact with a marine architect/trouble-shooter.

In the worst case I may have to replace the shaft (which was initially my immediate plan), and that would be an expensive task for me. That is the situation where I want a decent vibration measurement done at a fraction of the shaft cost, before I commit the money.
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Old 06-13-2018, 11:37 AM   #50
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Before you spend any money on vibration analysis, unbolt your flange bearing, account for your shaft sag by pulling up with 80-90 lbs force and then remount the flange bearing with rubber isolation (see how Aquadrive does it to get some ideas). You cannot mount the flange/thrust bearing directly to the hull/cross member. Your hull will amplify any prop and shaft noise like a bell.
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Old 06-13-2018, 03:42 PM   #51
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Did a little looking trying to figure out what your bearing is. Not much luck, I did find that the Emerson Morse devision that sells bearings is Sealmaster. I looked through their catalog trying to get a sense of their part numbering, couldn't find anything with your part number. Here is their catalog, maybe contact them if you want more info on your bearing.
http://takamolbearing.ir/old/pdf/Sea...ll_Bearing.pdf

Quote:
Originally Posted by SeahorseMarineDD54201 View Post




Thank you for making me aware of radial/axial thrust bearing.

Based on the marking (photo attached) on my thrust bearing and the parts list of a DD462 (mine does not have the detail), my thrust bearing is an Emerson Morse SFA-RFB-112C-1 3/4". I cannot find this part number from Googling yet to understand how it works. Will keep trying.

The attached pictures help to answer your questions:

1. The thrust bearing is mounted on a purpose built thick reinforced mounting plate (the big white wall between the thrust bearing and the Caden Shaft.

2. Near the end but not at the end, the Prop Shaft passes through the Thrust Bearing.

3. At the end of the Prop Shaft is a custom flange, that connects the Prop Shaft to the Caden Shaft.

4. By "Intermediate" Bearing I assume you mean the water lubricated whip bearing (the shaft was designed with only three bearings, the Cutlass Bearing and Prop End, the Thrust Bearing at the Caden Shaft/Transmission End, and the Whip Bearing right in the middle, though another Whip Bearing was inserted for trouble shooting purpose later). The "Intermediate" whip bearing is inside the stern tube about 1.8m from the Thrust Bearing.

5. The Shaft, Thrust Bearing, Cutlass Bearing, Whip Bearing are all standard Seahorse practice proven in the DD462s. The only difference from DD462 is the the longer length, requiring moving the Whip Bearing (DD462 has it right at the entrance of the stern tube). Though all these need to be re-checked, they are likely to be ok (except Whip Bearing location/qty). Seahorse is also aware of the trickiness of Caden Shaft (>3 deg offset and <.5 deg mis-alignment).

6. The engine and prop were run with the boat out of water (bearings lubrication maintained), and the prop rotated smoothly. The shaft was pulled and checked to be straight. Therefore I think the centerline is ok. Of course under load it may be a different story.


Thanks again for the tips and suggestions !
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Old 06-13-2018, 04:27 PM   #52
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I am thinking why not used a pipe, cut some teeth, using the transmission flange to center, then just rough drill the entire stern tube (and surrounding epoxy filling between tube and steel shaft log), and re-epoxy a larger stern tube.

Anyone has seen my "dreamed up" approach in practice by experienced yards in USA ?
If you have a steel shaft log, what purpose does the fiberglass tube serve?

I've done something similar to what you propose. Buy a hole saw of the appropriate diameter, remove the middle part and weld a pipe through it. This acts as the guide and the drive. A good quality hole saw will be "bi-metal", that is have high speed steel hardened teeth welded to a mild steel shell. The trickiest part is filling epoxy around the new tube without numerous gaps. The way to do that is to seal the low end (I used a turned piece with orings) and pump the epoxy in from the low end with a grease gun or similar tool. This will force it along the tube all the way to the other end, pushing the air ahead. Two strategies: use a thin epoxy so that it will run around the diameter as it goes, or fairly thick so that the pump pressure pushes it along which should also fill around the tube if the gap is relatively small. Do it on a cold day

But you have a steel boat. If a tube is needed, why not weld in a stainless steel one?
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Old 06-13-2018, 04:48 PM   #53
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Simple to weld in a new tube if all you're going to do is weld the ends. Probably you'll have to cut the hull open and make room, then weld the tube in, and weld the wound closed.

The problem is welding causes distortion due to the heat. How to not distort the tube while welding it??? Oversize the tube a bit and count on some distortion? Or just weld the tube on both ends, and don't heat the middle of the tube and risk distortion?
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Old 06-13-2018, 05:26 PM   #54
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Simple to weld in a new tube if all you're going to do is weld the ends. Probably you'll have to cut the hull open and make room, then weld the tube in, and weld the wound closed.

The problem is welding causes distortion due to the heat. How to not distort the tube while welding it??? Oversize the tube a bit and count on some distortion? Or just weld the tube on both ends, and don't heat the middle of the tube and risk distortion?


I think heat and distortion is exactly why he needs an arrangement with only two bearings, not three. And that leads to a properly sized shaft.
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Old 06-13-2018, 05:58 PM   #55
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Before you spend any money on vibration analysis, unbolt your flange bearing, account for your shaft sag by pulling up with 80-90 lbs force and then remount the flange bearing with rubber isolation (see how Aquadrive does it to get some ideas). You cannot mount the flange/thrust bearing directly to the hull/cross member. Your hull will amplify any prop and shaft noise like a bell.
All the suggestions about loosening flange bearing, lifting the shaft to account for sag, scoring and strobe light to check shaft whip, etc. are now coming together in my mind.

Also I need to re-check the Cardan Shaft as there may be some play.

Thanks to everyone for all the suggestions !

Actually I have one more piece of clue which I now realize could be very important. I will post it later.
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Old 06-13-2018, 06:03 PM   #56
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Did a little looking trying to figure out what your bearing is. Not much luck, I did find that the Emerson Morse devision that sells bearings is Sealmaster. I looked through their catalog trying to get a sense of their part numbering, couldn't find anything with your part number. Here is their catalog, maybe contact them if you want more info on your bearing.
http://takamolbearing.ir/old/pdf/Sea...ll_Bearing.pdf
Thanks for taking the time. I'll find out from Seahorse, and Emerson if necessary.

By sheer coincidence, yesterday I managed to move the Engine and Genset Batteries which sit on top of the floor board with better access to the flange bearing. Here is a close up picture (took me long time to load until I found a good network), and I don't think there is any rubber padding.
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Old 06-13-2018, 06:14 PM   #57
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If you're docked, you could double up the lines and do a bollard pull rather than running for a half hour in a straight line. In a past project, we did a vibration analysis and they used 3-4 pucks placed around the gear and could triangulate the source of the different vibrations based on frequency.
I have done some measurement with my Android Vibration Apps. I am no expert and could not really interprete the data.

Could you elaborate a bit on how you triangulated the source of vibration ?

Thanks in advance.
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Old 06-13-2018, 06:28 PM   #58
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If you have a steel shaft log, what purpose does the fiberglass tube serve?

I've done something similar to what you propose. Buy a hole saw of the appropriate diameter, remove the middle part and weld a pipe through it. This acts as the guide and the drive. A good quality hole saw will be "bi-metal", that is have high speed steel hardened teeth welded to a mild steel shell. The trickiest part is filling epoxy around the new tube without numerous gaps. The way to do that is to seal the low end (I used a turned piece with orings) and pump the epoxy in from the low end with a grease gun or similar tool. This will force it along the tube all the way to the other end, pushing the air ahead. Two strategies: use a thin epoxy so that it will run around the diameter as it goes, or fairly thick so that the pump pressure pushes it along which should also fill around the tube if the gap is relatively small. Do it on a cold day

But you have a steel boat. If a tube is needed, why not weld in a stainless steel one?
Another DD542 being built uses 2.5" shaft. Bill Kimley said it is only because the owner wants a Gardner engine which has a higher torque (Bill Kimley is adamant 2" is ok for my DD542, and from simply a torsion strength point of view, that is confirmed by a reputable shaft manufacturer).

The steel shaft log at about 5" diameter made it simple for different boats with different stern tube sizes. The entire shaft log is buried within the long keel. I think I came across an article on George Buehler's web, this is what the shaft log is used for. The stern tube is molded by Seahorse (I believe wrapping fiberglass around a pipe) probably just so that it can accommodate a 2" shaft. Otherwise how would they hold a 2" shaft in a 5" shaft log ?

Thanks for sharing the tricks on epoxy and hole saw. Very important for planning.

I am not sure what you mean by welding a SS tube. It sounds very difficult with the boat already built, to weld a SS tube within the shaft log, with left over epoxy lining the shaft log. The gap between the SS tube and steel shaft log also needs to be filled by epoxy ?
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Old 06-13-2018, 06:32 PM   #59
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Simple to weld in a new tube if all you're going to do is weld the ends. Probably you'll have to cut the hull open and make room, then weld the tube in, and weld the wound closed.

The problem is welding causes distortion due to the heat. How to not distort the tube while welding it??? Oversize the tube a bit and count on some distortion? Or just weld the tube on both ends, and don't heat the middle of the tube and risk distortion?
The entire shaft log is buried in the long keel filled with concerte/metal ballast. I cannot imagine any welding work done now.
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Old 06-13-2018, 08:29 PM   #60
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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.
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