Seahorse Marine Diesel Duck Vibration - Advice needed

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I think you're correct, with most of the shaft in the tube and you don't know if the tube is straight, the best option is only one bearing in the tube, the cutless at the rear. Problem now is that if your going to try and support that shaft with just the cutless and thrust bearing and you want to stay with a 40x unsupported length you're looking at a 3" shaft.
So it sort of looks like your original shaft is way undersize for the unsupported length, putting your whip bearing in the tube likely didn't help, either because the tube isn't straight or the tube and shaft don't have the same centerline and you've caused a misalignment. So maybe you went from a vibration caused be too much span between bearings to one caused by a bent shaft.
I was also thinking that it would be interesting to put dial indicators on the spinning shaft and see if there was any runout. But then figured that there is likely to be some and then you have to figure out how much is acceptable. Not sure how you do that.
Also looking at the pictures again it doesn't appear that there is any provision for moving the thrust bearing on it's plate. With the original set up with just a cutless and this bearing you didn't really need to move it, the bearing in the plate will take up misalignment. Adding a intermediate bearing you would then have 3 points that have to be in alignment, so you will have to have a provision for moving the thrust bearing on the plate. It'd be interesting to know that now that you have the whip bearing in the tube what would happen if you unbolt the thrust bearing from the plate, you'd have to take the carden shaft off first, but I bet the thrust bearing moves when you take the bolts out. Bet you've put a bow in the shaft with the whip bearing.
Another thing to look at is the carden shaft, carden joints can only take misalignment in one plane. Usually these things are used when your shaft angle and engine angle are different. But then was has to happen is that you need to know that your engine centerline lines up with your prop shaft centerline. That's on the vertical axis, basically if you are standing looking down on your engine and shaft they have to be in a straight line
You know, if this was my boat, I'd be looking to see if I could cut that shaft tube off short enough that I could put an intermediate bearing on a separate mount ahead of the tube.
 
SeahorseMarineDD54201 said:
If I understand you correctly, I mentioned this concern as well that the Caden shaft being extended, can also deflect.

But how to measure the deflection if any ? the surface of the Caden shaft is rough so I cannot use a depth gauge nor a laser.
Click to expand...

I understand, assuming the telescoping part is is square or some other shape with a matching center rod. I've seen these take up to 1000 RPM.

If the U joint yokes are in good alignment and there isn't a lot of play in the telescoping part, then probably your vibration is likely in the driveshaft, and that's the most expensive repair location...

The truck that twisted the driveshaft only had about 20 degrees (est) of twist where the drive line tube was welded on the two yoke ends. Here, we used thinwall tubing cut on a lathe and welded it on the two yoke ends. We had to cut the tubing wall square (after it sheared and twisted) and reweld it.

One option to remove the cardan shaft from suspicion is to replace it with a fixed tube unless your engine moves enough to require the telescoping action. Any machine shop should be able to do that without much cost, just measure the distance needed accurately.

Do you have a photo of the cardan shaft?
 
sean9c said:
So your thrust bearing is just a flange bearing bolted to a plate. Weird in that flange bearings aren't usually even rated for axial load only radial but this one is intended to take axial loading. Certainly a bare bones solution, it's about a $100 bearing. By the numbering you can figure that they've turned the shaft down to 1-3/4" at the bearing. That way the thrust is taken by the shoulder of the turned down shaft hitting the bearing. How do you align that thrust bearing? The bearing itself will adjust to the plate being out of square to the shaft but something needs to be adjustable for centerline.
The carden shaft is just standard with a joint at each end, you need the splined slip joint to take up any length changes that might occur. The engine moving on it's mounts is could cause a length change. Only problem with this style shaft is that you can get some chattering from the splined slip joint. It is critical that the 2 carden joints are in phase, you can't just put the 2 pieces together any old way.
It appears in your drawing that there are 2 bearings in the shaft tube. How do you know the tube is straight? Doesn't do any good to check the shaft for straight on the bench and then put it in a tube that you don't know is straight.
Have to say that Seahorse did about the bare minimum in materials and engineering with this set up.
Really no way you're going to resolve this on the internet. You need someone who knows what they're doing at the boat. This stuff isn't complicated you just need to understand whaOt you're doing and work through the steps.
Click to expand...

Thank you for your observations, I am getting a lesson here.

DD462s which do not vibrate, use the same configuration as my DD542, only that DD542 is longer.

I believe Seahorse use the Prop end Cutlass Bearing and the Whip Bearing to define the center line of the shaft. Once shaft is installed, they probably would fasten the thrust bearing accordingly (which I realize now is a flange bearing). In other words the thrust bearing probably does not defined the center line, and does not constrain the shaft radially. I will ask Seahorse worker to confirm.

This arrangement works for DD462, I believe partly because the shaft is shorter (by 30cm approx), that Cutlass/Whip bearings are at opposing ENDS of the stern tube is sufficient to radially support the shaft.

I worry this does not work for DD542. Different from DD462, the shaft being longer requires the Whip Bearing to be placed near the middle of the Stern Tube, and now the thrust bearing acts as a support against radial force. Therefore we have three bearings to constrain the shaft. I mentioned somewhere in another reply that an additional whip bearing was inserted and got stuck, suggesting the stern tube may not be straight.

Though DD542 shaft may be over-constrained by 3 bearings, the fact is that the shaft is straight ! The engine/shaft/prop were run with the boat out of water (lubrication to bearings maintained), the prop turned very smoothly. Would it be any different with the boat in the water and drive train stressed with load ?

Another feedback below suggests that I should remove the whip bearing (s), and it begins to make sense to me. But I have some concerns as well to be elaborated in reply to that comment.
 
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D.Duck44 said:
Have you checked that the flanges at each end of the carden shaft are absolutely parallel and have no run-out?
Click to expand...

Bill Kimley made a jig, a cylinder with two flanges on each end approximately the length of the Caden Shaft. The Caden Shaft was removed, one end of the jig was fastened to the prop shaft, and the other flange face was checked with feeler gauge for alignment with the transmission flange.

I have not mentioned this before, that this means the Caden shaft does not have the 3 deg off set required for lubrication. But all DD462s are built the same way, Seahorse workers said this should not be the source of vibration (though it can introduce other issues), and Bill Kimley says lubrication would happen when the engine and shaft move around. I suspect this offset needs to be re-done, but for investigating vibration, I am prepared to focus on other potential causes.
 
sean9c said:
I think you're correct, with most of the shaft in the tube and you don't know if the tube is straight, the best option is only one bearing in the tube, the cutless at the rear. Problem now is that if your going to try and support that shaft with just the cutless and thrust bearing and you want to stay with a 40x unsupported length you're looking at a 3" shaft.
So it sort of looks like your original shaft is way undersize for the unsupported length, putting your whip bearing in the tube likely didn't help, either because the tube isn't straight or the tube and shaft don't have the same centerline and you've caused a misalignment. So maybe you went from a vibration caused be too much span between bearings to one caused by a bent shaft.
I was also thinking that it would be interesting to put dial indicators on the spinning shaft and see if there was any runout. But then figured that there is likely to be some and then you have to figure out how much is acceptable. Not sure how you do that.
Also looking at the pictures again it doesn't appear that there is any provision for moving the thrust bearing on it's plate. With the original set up with just a cutless and this bearing you didn't really need to move it, the bearing in the plate will take up misalignment. Adding a intermediate bearing you would then have 3 points that have to be in alignment, so you will have to have a provision for moving the thrust bearing on the plate. It'd be interesting to know that now that you have the whip bearing in the tube what would happen if you unbolt the thrust bearing from the plate, you'd have to take the carden shaft off first, but I bet the thrust bearing moves when you take the bolts out. Bet you've put a bow in the shaft with the whip bearing.
Another thing to look at is the carden shaft, carden joints can only take misalignment in one plane. Usually these things are used when your shaft angle and engine angle are different. But then was has to happen is that you need to know that your engine centerline lines up with your prop shaft centerline. That's on the vertical axis, basically if you are standing looking down on your engine and shaft they have to be in a straight line
You know, if this was my boat, I'd be looking to see if I could cut that shaft tube off short enough that I could put an intermediate bearing on a separate mount ahead of the tube.
Click to expand...

As I replied to another comment, I see the point that for the longer DD542, the Whip Bearing and thrust bearing together may over constrain the shaft (as opposed to DD462 with a shorter shaft, the thrust bearing PROBABLY does not).

Having said that if under no load, the shaft is straight: The engine and shaft were fire up while the boat is on dry dock (bearing lubrication maintained), and the prop turned very smoothly. However in the water with load, I wonder what would happen. Perhaps the aft section of the shaft would still be straight, but the forward section may deflect if the thrust bearing does not constrain the shaft ... yet according to Bill Kimley the thrust bearing does act against radial forces ...

At this point I plan to proceed with a vibration measurement/analysis.

I also need to plan for increasing the diameter of the shaft subject to vibration analysis results. The fiberglass stern tube inner diameter is 2-5/8" for a 2" shaft. So if I change shaft to 2.5":

1. The Duramax Whip/Cutlass bearings are already the thin wall model. Can't change that.

2. I can bore out the two ends of the stern tube, and have Cutlass/Whip bearings located at opposing ends (same as DD462). But the stern tube at 2-5/8" is still very tight, especially if it has a sag. Also the bearings would be about 3.3m apart which does not conform to the 40x diameter guideline.

3. I can go for a much thicker shaft, may be 3" and get rid of the whip bearing. That means I need to use a stern tube with 3-5/8" inner diameter. I can ream the existing stern tube for 3.3 meters, or I can drill it out (along with epoxy filling between the tube and the steel shaft log) and put in a new tube. Any opinion if either approach is practically and have been tried ? Any opinion which is better ?


** Still thinking about your suggestion related to Caden Shaft
 
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If you are going to have 2 bearings in the shaft tube you are going to have to have a way to adjust the position of the flange bearing on it's plate. You have 3 points of contact with your shaft they all have to be in alignment.
Now if you do indeed find that the position of the flange bearing needs to be adjusted that will also throw off the alignment of the carden shaft. So you might then have to shift the engine to compensate.
Seahorse is doing the exact right thing in giving you a solid flanged shaft to replace the carden shaft to check its alignment.
Checking your shaft for straight by spinning the shaft with the engine in the yard tells you nothing. Maybe decouple the shaft from the carden shaft and spin the prop by hand might tell you a little but still the boat on stands and the boat floating might be 2 different alignments.
Still think the first thing I'd do is take the carden shaft off and unbolt the flange bearing for it's plate and see if it shifts. What you're trying to see is where the shaft is pointing given it's held by the 2 bearings in the tube. So the end of the shaft needs to be free to move. To do it right you also want to try and take any sag out of the shaft. What I've done is take 1/2 the weight of the length of shaft from it's last support + the weight of the flange and all the stuff on the end of the shaft, get a spring scale attached to the shaft and lift up that amount. Now the shaft should, sort of, be straight, see where it points, turn it by hand and see what moves. All this is easy to do and won't cost anything, it's an easy test to possibly eliminate a variable or likely indicate the problem.
I'd be curious where you find someone to do a vibration analysis and what they tell you. Will they tell you what to change? Have usually found these things are worked out by thinking about it and working through the basics
 
I agree with Sean9c's plan of attack. Make sure the flange bearing is fully aligned including accounting for the shaft sag. With 1.8m distance to the whip bearing, your unsupported shaft weight is about 63 lbs plus whatever your flange bearing weighs.

In addition, it seems your flange bearing is hard mounted. This will transmit any propeller and shaft noise to the hull. Take a look at how Aqua Drive mounts their thrust bearings. Support structure and thrust bearing are isolated via rubber bushings.
 
stubones99 said:
I understand, assuming the telescoping part is is square or some other shape with a matching center rod. I've seen these take up to 1000 RPM.

If the U joint yokes are in good alignment and there isn't a lot of play in the telescoping part, then probably your vibration is likely in the driveshaft, and that's the most expensive repair location...

The truck that twisted the driveshaft only had about 20 degrees (est) of twist where the drive line tube was welded on the two yoke ends. Here, we used thinwall tubing cut on a lathe and welded it on the two yoke ends. We had to cut the tubing wall square (after it sheared and twisted) and reweld it.

One option to remove the cardan shaft from suspicion is to replace it with a fixed tube unless your engine moves enough to require the telescoping action. Any machine shop should be able to do that without much cost, just measure the distance needed accurately.

Do you have a photo of the cardan shaft?
Click to expand...

Here are photos of Caden Shaft:

https://drive.google.com/open?id=1scdA2ujXuNztCiz6TFkWDNBre6IFbZGo

open
 
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sean9c said:
If you are going to have 2 bearings in the shaft tube you are going to have to have a way to adjust the position of the flange bearing on it's plate. You have 3 points of contact with your shaft they all have to be in alignment.
Now if you do indeed find that the position of the flange bearing needs to be adjusted that will also throw off the alignment of the carden shaft. So you might then have to shift the engine to compensate.
Seahorse is doing the exact right thing in giving you a solid flanged shaft to replace the carden shaft to check its alignment.
Checking your shaft for straight by spinning the shaft with the engine in the yard tells you nothing. Maybe decouple the shaft from the carden shaft and spin the prop by hand might tell you a little but still the boat on stands and the boat floating might be 2 different alignments.
Still think the first thing I'd do is take the carden shaft off and unbolt the flange bearing for it's plate and see if it shifts. What you're trying to see is where the shaft is pointing given it's held by the 2 bearings in the tube. So the end of the shaft needs to be free to move. To do it right you also want to try and take any sag out of the shaft. What I've done is take 1/2 the weight of the length of shaft from it's last support + the weight of the flange and all the stuff on the end of the shaft, get a spring scale attached to the shaft and lift up that amount. Now the shaft should, sort of, be straight, see where it points, turn it by hand and see what moves. All this is easy to do and won't cost anything, it's an easy test to possibly eliminate a variable or likely indicate the problem.
I'd be curious where you find someone to do a vibration analysis and what they tell you. Will they tell you what to change? Have usually found these things are worked out by thinking about it and working through the basics
Click to expand...


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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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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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.
 
DDW said:
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.
Click to expand...

:thumb:
 
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.

SeahorseMarineDD54201 said:
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:
Click to expand...
 
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.
 
sean9c said:
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.
Click to expand...
For my info, what makes you think this is cheap setup?

L
 
Delfin said:
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.
Click to expand...

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 ?
 
DDW said:
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.
Click to expand...

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.
 
sean9c said:
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.
Click to expand...

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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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.
 
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/Sealmaster_Ball_Bearing.pdf

SeahorseMarineDD54201 said:
open


open


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 !
Click to expand...
 
SeahorseMarineDD54201 said:
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 ?
Click to expand...

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?
 
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?
 
stubones99 said:
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?
Click to expand...



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.
 
gsholz said:
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.
Click to expand...

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.
 
sean9c said:
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/Sealmaster_Ball_Bearing.pdf
Click to expand...

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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stubones99 said:
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.
Click to expand...

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.
 
DDW said:
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?
Click to expand...

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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stubones99 said:
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?
Click to expand...

The entire shaft log is buried in the long keel filled with concerte/metal ballast. I cannot imagine any welding work done now.
 
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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