Reply
 
Thread Tools Search this Thread Display Modes
 
Old 06-26-2018, 04:34 PM   #121
Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 4,562
So do you think the 2" shaft is impacting the 2 5/8" ID FG tube? Shaft would have to be quite a bit out of whack to get 5/16" eccentric motion. We get freaked out with 0.030" runout, way less than 0.312" runout.

Are you seeing visible runout in shaft between gland and transmission?
__________________
Advertisement

Ski in NC is offline   Reply With Quote
Old 06-26-2018, 11:46 PM   #122
Veteran Member
 
City: Zhuhai
Country: China
Join Date: Jun 2018
Posts: 66
Quote:
Originally Posted by Ski in NC View Post
So do you think the 2" shaft is impacting the 2 5/8" ID FG tube? Shaft would have to be quite a bit out of whack to get 5/16" eccentric motion. We get freaked out with 0.030" runout, way less than 0.312" runout.

Are you seeing visible runout in shaft between gland and transmission?
Not being mechanically hands on, I can fill my imagination with very drastic scenarios, and the shaft whirling against the stern tube is conceivable. However I don't think it happened otherwise it would have broken off ?

More interestingly is how you gauge/measure shaft whirling and runout at 0.03" ? Was it measured on boat or in machine shop ? How how to apply load comparable with a propeller ?

The next big plan is a Typhoon Shelter sea trial. With everyone's comments, I have an idea how to check for shaft flex (laser, strobe light, scoring, etc..) Right now I have no evidence of "gland and transmission". But I don't know what you mean by "gland".
__________________

SeahorseMarineDD54201 is offline   Reply With Quote
Old 06-27-2018, 07:40 AM   #123
Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 4,562
You can see a shaft wobble of 0.030" with bare eye. Gland is just a term for shaft packing box or dripless seal. Just watch the exposed part of the shaft visible in engine room and see if it wiggles (tech term is runout). Runout usually more pronounced further aft from shaft coupling to gear.

You can observe this tied to the dock with engine at low power, in gear. How much power you can add while tied depends on how well it is tied and what is around the dock.
Ski in NC is offline   Reply With Quote
Old 08-18-2018, 07:27 PM   #124
Veteran Member
 
City: Zhuhai
Country: China
Join Date: Jun 2018
Posts: 66
Progress Update - Finding the Cause

It has been quite a while since I got all the advices (with gratitude) from the forum (last thread being #123 on 27 June 2018), and as a gesture of appreciation, I will keep all updated on the current status.

This is the first thread, to report on the progress/status of finding the cause of the vibration. A second thread will follow to report on the progress/status of shaft replacement, so all forum members can take a breather in between.

To summarize all previous threads (up to #123), which started off with my initial concern of the shaft quality causing the vibration on my DD542 (while DD462s with almost identical design has none):

1. Whip Bearing equally dividing the shaft can cause harmonics.

2. Shaft may sag between Whip Bearing and Thrust Bearing during alignment, resulting in wrong Thrust Bearing location.

Also mine (and all DD462s) is really a Flange Bearing with no rubber padding. The mounting can amplify the noize, and the bearing cannot be adjusted if incorrectly aligned (therefore Aquadrive suggested).

3. Stern Tube may have a sag during alignment (possibly causing Whip Bearing No. 2 to be stuck).

4. The shaft is supported at three points: Cutless Bearing, Whip Bearing, Thrust Bearing (Whip Bearing No. 2 will be removed). Aligning at three points is tricky.

5. Prop blades exert differential pressure (and imbalance) as each passes under the hull.

6. Carden Shaft may have play.

7. If it is the shaft that vibrates, it can be observed if pronounced, with laser, scoring, strobe light, dial gauge, “wiggling”, etc. A lot more specifics can be confirmed, before going for an expensive trial and error boat lift and shaft change.

8. Hull “panting” is unlikely. Rudder can also cause vibration.

9. Vibration measurement and data analysis if done professionally, can locate the source of vibration.

10. I would do a sea trial and attempt to cover all advices given to me.

11. Bill Kimley at Seahorse asked me to find an vibration analyst, and said he would replace the shaft with a name brand in Hong Kong.

Here is the summary of progress and status on finding the cause of vibration:

12. Shaft sag during factory alignment is unlikely. Seahorse puts a temporary Whip Bearing at the end of the Stern Tube to support shaft weight. The bolting location of the Thrust Bearing is then decided. On the other hand, Stern Tube sag remains at least a theoretical concern for my longer DD542 (no problem for the shorter DD462).

13. Seahorse seems to be experienced with 3 point alignment (Cutless Bearing, Whip Bearing, Thrust Bearing, and the temporary Whip Bearing) for DD462s, and DD542 is done the same way.

Strictly speaking Seahorse aligns Cutless Bearing and Whip Bearing. The location of Thrust Bearing is then decided according to the line defined by Cutless Bearing and Whip Bearing, and the weight of the shaft is supported by the temporary Whip Bearing to preclude sagging.

14. Carden Shaft removed and re-checked for phasing and play. All checked out.

15. My 6 cylinder engine, 3:1 Gear Box, and 3 blade propeller theoretically re-inforce each other at multiples of 3 (pointed out by a professional vibration consultant). However with the Carden Shaft disconnected, no vibration was felt with the engine running in gear (therefore Gear Box resonance is unlikely). Also as already noted, changing the prop to 4 blade did not eliminate vibration.

16. Here is the big one: The shaft equally divided by the Whip Bearing would create a frequency pair, the frequencies are nearly equal yet different. This would result in the acoustic phenomenon “Beat”, which accounts for the cycling of vibration intensity felt at high loading (see Thread #1).

In other words, unless the frequency pair comes from another source, we could say with high confidence, the shaft is vibrating. However the cause and the most effective remedy of the shaft vibrating remain to be decided. It may well be the shaft material too weak, or it may be excessive load, or it may be alignment, etc..

17. Jeff Fritges (a professional vibration analyst recommended by JustBob at MV Mahalo, Thank you !) recognized the “Beat” phenomenon above. To determine the exact component/cause, he suggested to do measurement and data analysis. Bill Kimley at Seahorse decided no, because he will replace the shaft and re-align the entire drivetrain anyway. Bill also wants a thicker shaft. The next thread will report on the progress and status of shaft replacement.

18. Bill Kimely took the advice of a fellow DD owner, to take a ride on my boat (about an hour), along with a friend who is a professional mechanic on ocean liners. We did that on 23 July.

Again with the smaller fixed 4 blade prop yielding 50% power, we all observed the vibration is not bad at low power, but very bad at medium power (50%), with no “beat” phenomenon (either because power is not high enough, or because Whip Bearing No. 2 now broke up the original frequency pair created by Whip Bearing No. 1 at the middle of the shaft, or both). Also the mechanic friend noted the vibration to be concentrated at the aft of the Aft State Room (Master State Room). I also took the opportunity to check the salon and Forward State Room. There was none .

19. I took the boat out immediately after Bill Kimley left, for a one week cruise, hoping to do a sea trial in an empty typhoon shelter, using suggestions given in the forum.

The one hour ride with Bill, and this cruise is the very first time the boat is taken out after the last yard visit in March 2017, where Whip Bearing No. 2 was inserted and the prop changed to a smaller one.

For the first couple of days we were anchoring for some fun, but we lost the Gear Box control, then the Engine Display. The causes are now determined and problems fixed, but at the time I was spooked enough that I returned to port without going to the empty typhoon shelter.

20. After the cruise with the engine running for no more than 24 hours, I dived to clean some hull side barnacles I missed before. By habit I turned the prop by hand. Each turn is something like 90 degrees before the blade is rotated out of its lever.

To my surprise at the END of EACH turn, I felt the shaft or something in there vibrating. I pushed the prop up-down and sideways, but there was no play. I got back on deck, started the engine, and the whole boat shook violently when I put it in gear at lowest rpm. I immediately put it back in neutral, then in gear again, and the vibration was gone. Next day I dived and hand rotated the prop again, there was no vibration. Another day passed and I started the engine, put in gear, and the boat shook violently. Then as I did before, putting gear in neutral then back in gear, the vibration is again gone. I did not do a follow up dive.

In fact this violent shaking happened occasionally before and would disappear by itself once geared out then in. I was told at the time a garbage bag caught on the prop can do this. This is the first time I confirmed nothing was caught on the prop, it shakes, then shakes itself off.

However something must have gotten loose during the <24 hr cruise, that this shaking happened three times over 4 occasions of engine start within 2 weeks. My gut feel is it takes some time with the drivetrain inactive, for something to “settle”, in order to build up the mechanism of shaking. I wonder if it is caused by Whip Bearing No. 2 stuck axially, yet not fastened in place radially. Someone suggested it could be the Gear Box rubbing plates. I will experiment with engine start at varying frequency (say once a day vs once a week), to see how long it takes for the build up.

21. Anyway I hope Bill Kimley’s promise to replace the shaft with a thicker one, and re-align the entire drivetrain (in Hong Kong) would fix all. That’s another update in the next thread to come in a couple of days, some of it more frustrating than others. Take a breather for now and thank you all for reading.
SeahorseMarineDD54201 is offline   Reply With Quote
Old 09-06-2018, 05:23 AM   #125
Veteran Member
 
City: Zhuhai
Country: China
Join Date: Jun 2018
Posts: 66
Progress Update - Approach to Fixing the Vibration

In Post #124 I gave an update on finding the cause of vibration. This (belated) post is meant to give an update on the progress of fixing the vibration.

However as I have a very specific question on the approach to fixing the vibration, hopefully to bring some suggestions back, I will make another post after, to summarize the progress of the work.

Seahorse wants to replace the 2” shaft with a 2-”. In order to accommodate the thicker shaft, Seahorse built a reaming tool to enlarge the Stern Tube. It consists of:
1. a 10” long pipe diametrically (2.5”) precision fitted into the as is Stern Tube
2. a 2.75” diameter reaming knife at the tail of the pipe
3. a 2.5” diameter reaming knife at the head of the pipe.

The precision fitting between the pipe and the Stern Tube means the tool is self-aligning (see below for details). IN ADDITION there are other critical features and components to further enhance alignment (but these are not needed for discussion here). The process:

1. The Reamer would be pushed in from the Prop end of the Stern Tube, head first.

2. The Head Reaming Knife at exactly the diameter of the as is Stern Tube, will clean off any imperfection. After all something must be in the tube when Whip Bearing No. 2 was pushed in from the Prop end, with the Shaft in place (checked to be straight back in 2016).

3. The 10” precision fitted pipe will align itself with the cleaned up Stern Tube, so by the time the Tail Reaming Knife reaches the Stern Tube, it would enlarge the tube precisely aligned.

4. For the Prop end, only the very first 10+” inches need to be precisely reamed. That is the location of the Cutlass Bearing (8" long). But the Reamer will continue on until it gets near the location of the Whip Bearing.

5. The Reamer would then be pushed in from the Gear end of the Stern Tube, head first. The same process (2,3) above would happen. However precision reaming must be maintained for (my estimate) about 2 ft, to reach the planned location of the Whip Bearing (which is a bit forward of the current location, as the current location dividing the shaft into equal halves, will cause harmonics and “beat”).

The reaming tool was built and tried over a short section of a dummy Stern Tube, and the angular error over that short section (presumably the length of the Cutlass Bearing or about 8”) was less than 5 thousands of an inch. The Seahorse engineer is very satisfied with the trial results, and is adding an intermediate reaming knife to ease the load off the Tail Reaming Knife.

My concern is at least theoretically, the sag of the Stern Tube. If there is already a sag, no matter how precise the Reamer is aligned with the bent Stern Tube, the most critical sections of the reamed tube (ie. at the location of the Cutlass Bearing and the Whip Bearing) would still have an axial angular error, which may be significant to have caused the vibration in the first place. Of course a stronger shaft could withstand the stress better, nonetheless unnecessarily.

The sag obviously cannot be observed by the naked eyes, otherwise Seahorse workers would have stopped work back in the yard. So I am wondering if there is another way to check for the sag before we start reaming. For example we could stick a long straight 2.5” pipe through, or we could use a surveyor’s scope, or something. I would very much appreciate some suggestions from the community.
SeahorseMarineDD54201 is offline   Reply With Quote
Old 09-06-2018, 07:55 AM   #126
Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 4,562
Reaming out the tube would not be first on my list. That is a technical challenge with many potential pitfalls.

Have you tried a name-brand shaft as discussed many times way back?

Can you post a sketch of exactly what bearings, shaft pieces, etc are in the shaft line? What is this about a Cardan joint?
Ski in NC is offline   Reply With Quote
Old 09-06-2018, 09:00 AM   #127
Veteran Member
 
City: Zhuhai
Country: China
Join Date: Jun 2018
Posts: 66
Quote:
Originally Posted by Ski in NC View Post
Reaming out the tube would not be first on my list. That is a technical challenge with many potential pitfalls.

Have you tried a name-brand shaft as discussed many times way back?

Can you post a sketch of exactly what bearings, shaft pieces, etc are in the shaft line? What is this about a Cardan joint?
This thread started as a my request for advice on replacing the shaft with a name brand. Seahorse then decided to do so, but while at it, also wants to increase the shaft diameter.

The diagram showing various drive train components is again attached below, showing in sequence:

Prop (now a smaller powered down 4 blade fixed prop for trial purpose)
Cutlass Bearing
Whip Bearing No. 2 (inserted from Prop end for trail purpose, to be removed)
Whip Bearing (will be relocated forward for concern on harmonics and "beat")
Shaft Seal
Thrust Bearing
Cardan Shaft
(Gear Box/Engine not shown)
Attached Thumbnails
Click image for larger version

Name:	Shaft.jpg
Views:	38
Size:	64.0 KB
ID:	80614  
SeahorseMarineDD54201 is offline   Reply With Quote
Old 09-06-2018, 09:30 AM   #128
Guru
 
City: Melbourne, FL
Country: USA
Join Date: Dec 2014
Posts: 1,264
I would be leery of a hand built reamer, especially if there is only a single fly cutter, since the torque will deflect the shaft and not give you a straight cut. There should be at least two or maybe three cutter bits on the reamer, and the alignment should be carefully controlled.

I noticed there was a Diesel Duck 54 in Alaska on Yachtworld. Have they had any of the problems you've had with yours? If not, what's different with their boat than yours?
stubones99 is offline   Reply With Quote
Old 09-06-2018, 12:04 PM   #129
Senior Member
 
City: Anacortes
Country: United States
Join Date: Mar 2016
Posts: 183
If your stern tube is not straight now and the reaming gadget just indexes off the existing tube won't you just end up with a larger tube that is also not straight? But maybe the ability to then fit a larger shaft fixes the issue.
I've always found that understanding what the problem is before attempting a repair works best. This sounds more like a shotgun approach to the issue.
sean9c is offline   Reply With Quote
Old 09-06-2018, 04:48 PM   #130
Veteran Member
 
City: Zhuhai
Country: China
Join Date: Jun 2018
Posts: 66
Quote:
Originally Posted by stubones99 View Post
I would be leery of a hand built reamer, especially if there is only a single fly cutter, since the torque will deflect the shaft and not give you a straight cut. There should be at least two or maybe three cutter bits on the reamer, and the alignment should be carefully controlled.

I noticed there was a Diesel Duck 54 in Alaska on Yachtworld. Have they had any of the problems you've had with yours? If not, what's different with their boat than yours?
Thanks for the advice of more cutter bits.

As far as I know (and I did my homework), there is only one 55' (or thereabout) DD built by Seahorse before my DD542-01. This is a full sized 55' much bulkier, while DD542-01 is merely a stretched/lengthened version of DD462s.

George Buehler said (see Post #1 Item 5 and Item 6) the first DD55 (presumably the same 55' and the one you saw) vibrated so bad that the coupling came off (probably no Cardan Shaft). George said the problem was completely fixed by replacing the shaft with a name brand, and re-aligning the drive train, all done in a USA yard. Bill Kimley told me last week George was wrong, that the vibration had nothing to do with the shaft, but Bill did not explain what in his opinion was wrong (before he told me to leave his office, another story ..).

Indeed this whole thread I put out asking for advices on changing the DD542-01 shaft to a name brand, started with George's suggestion (again see Post #1).
SeahorseMarineDD54201 is offline   Reply With Quote
Old 09-06-2018, 04:54 PM   #131
Veteran Member
 
City: Zhuhai
Country: China
Join Date: Jun 2018
Posts: 66
Quote:
Originally Posted by sean9c View Post
If your stern tube is not straight now and the reaming gadget just indexes off the existing tube won't you just end up with a larger tube that is also not straight? But maybe the ability to then fit a larger shaft fixes the issue.
I've always found that understanding what the problem is before attempting a repair works best. This sounds more like a shotgun approach to the issue.
Agree with you that IF the Stern Tube is not straight, the reamed Stern Tube would still not be straight.

This is why I am asking for suggestions, on how to check the straightness of the Stern Tube, and most importantly, how to determine the acceptable amount of sag (theoretically every Stern Tube has a bit of sag, I believe).

Bill Kimley initially agreed to replace the Stern Tube with a name brand. Then he decided to increase the diameter while at it. So I would say this is a stretched solution, and did not start with a shot gun. Bill was adamant the shaft was not too thin; perhaps he changed his mind.
SeahorseMarineDD54201 is offline   Reply With Quote
Old 09-06-2018, 08:20 PM   #132
Senior Member
 
BIG CAT's Avatar
 
City: Kiln,MS
Country: USA
Join Date: May 2016
Posts: 312
I'm no machinist but a few thing that come to mind.
First thing is how thick is the tube and how much strength will be lost when they ream it out to a larger dia. Also I'm not a fan of the tool you're describing. The straightness of the existing tube and maintaining a straight cut with the tool described seems like a daunting task. A few things that come to mind about the tool. With the reamer on the tail end there's nothing to stop the end of the cutter from deflecting. doing a single cutting pass while removing that much material seems very ambitious and the more material you remove in a single pass the greater the chance it drifts/deflects. imo i would put the a tail piece after the cutter to help keep it straight and make a small cut first then check the tube for size/straightness then step up the size of cutters till you reach the desired size.
BIG CAT is offline   Reply With Quote
Old 09-06-2018, 08:44 PM   #133
Veteran Member
 
City: Zhuhai
Country: China
Join Date: Jun 2018
Posts: 66
Quote:
Originally Posted by BIG CAT View Post
I'm no machinist but a few thing that come to mind.
First thing is how thick is the tube and how much strength will be lost when they ream it out to a larger dia. Also I'm not a fan of the tool you're describing. The straightness of the existing tube and maintaining a straight cut with the tool described seems like a daunting task. A few things that come to mind about the tool. With the reamer on the tail end there's nothing to stop the end of the cutter from deflecting. doing a single cutting pass while removing that much material seems very ambitious and the more material you remove in a single pass the greater the chance it drifts/deflects. imo i would put the a tail piece after the cutter to help keep it straight and make a small cut first then check the tube for size/straightness then step up the size of cutters till you reach the desired size.
Thanks for the comment.

According to Bill Kimley, there is plenty of material on the Stern Tube. I tend to agree just by looking at the percentage. We are reaming about 1/8" wall thickness from approximately 1" total wall thickness. DD542-02 (still being built) follows the same approach (but done on a machine shop instead of on the boat). I will re-confirm the wall thickness.

As I said in Post #125, there are also other components and features to help alignment. Once the Reamer fully moves into the Stern Tube, there is an centering device fixed at the end of the tube, so the tail of the Reamer would always remain centered and aligned, while the head of the Reamer is indexed to the as is Stern Tube bore.

Anyway the whole process needs to be rehearsed in the yard to prove the concept and tool. The only thing I think difficult to rehearse is a Stern Tube with a sag.
SeahorseMarineDD54201 is offline   Reply With Quote
Old 09-07-2018, 11:48 AM   #134
Senior Member
 
City: Anacortes
Country: United States
Join Date: Mar 2016
Posts: 183
There are all sorts of line boring machines out there. Portable line boring machines are a standard in the heavy equipment industry. I know they're some that'll go 96", likely some that'll go longer. At least that way you aren't just following the old tube.
Also in my little town we have a shipyard, Dakota Creek, I've seen them do line boring on stern tubes and rudder posts on boats on their ways. This has got to be standard stuff in shipbuilding and maintenance, at least in this part of the world. Also guessing that they have inspection methods and techniques to determine what action is required.
I'm thinking a little googling and asking questions could go a long way it figuring out the best plan.
Also wondered if you could bore your stern tube oversize, put the cutless bearings on the shaft slide the whole thing in the tube then pot the OD's of the bearings in epoxy. I've done this in fiberglass boats, easy way to get near perfect alignment.
sean9c is offline   Reply With Quote
Old 09-08-2018, 12:42 AM   #135
Veteran Member
 
City: Zhuhai
Country: China
Join Date: Jun 2018
Posts: 66
Quote:
Originally Posted by SeahorseMarineDD54201 View Post
Thanks for the comment.

According to Bill Kimley, there is plenty of material on the Stern Tube. I tend to agree just by looking at the percentage. We are reaming about 1/8" wall thickness from approximately 1" total wall thickness. DD542-02 (still being built) follows the same approach (but done on a machine shop instead of on the boat). I will re-confirm the wall thickness.

As I said in Post #125, there are also other components and features to help alignment. Once the Reamer fully moves into the Stern Tube, there is an centering device fixed at the end of the tube, so the tail of the Reamer would always remain centered and aligned, while the head of the Reamer is indexed to the as is Stern Tube bore.

Anyway the whole process needs to be rehearsed in the yard to prove the concept and tool. The only thing I think difficult to rehearse is a Stern Tube with a sag.

Correction on the wall thickness of the Stern Tube as is: It is about 0.65". Inner diameter is 2.625" and outer is about 4".

Again Bill Kimley said there is plenty of material to work with. I know DD542-02 (still being built) uses a 2.5" shaft (as compared with 2.25" being planned for my DD542-01) also uses the same Stern Tube and Shaft Log, with the Stern Tube reamed for the larger 2.5" shaft (though done in a machine shop instead of on a boat).
SeahorseMarineDD54201 is offline   Reply With Quote
Old 09-08-2018, 12:49 AM   #136
Veteran Member
 
City: Zhuhai
Country: China
Join Date: Jun 2018
Posts: 66
Quote:
Originally Posted by sean9c View Post
There are all sorts of line boring machines out there. Portable line boring machines are a standard in the heavy equipment industry. I know they're some that'll go 96", likely some that'll go longer. At least that way you aren't just following the old tube.
Also in my little town we have a shipyard, Dakota Creek, I've seen them do line boring on stern tubes and rudder posts on boats on their ways. This has got to be standard stuff in shipbuilding and maintenance, at least in this part of the world. Also guessing that they have inspection methods and techniques to determine what action is required.
I'm thinking a little googling and asking questions could go a long way it figuring out the best plan.
Also wondered if you could bore your stern tube oversize, put the cutless bearings on the shaft slide the whole thing in the tube then pot the OD's of the bearings in epoxy. I've done this in fiberglass boats, easy way to get near perfect alignment.
Not sure what's available in China or in Hong Kong. Anything could be made available for a price, and I believe Bill Kimley had taken that into account.

Will continue googling. However I am curious about the over-size boring idea. Are you saying to deliberately bore the Stern Tube larger than the planned Whip Bearing/Cutlass Bearing ? How much larger to bore ? The Whip Bearing has to be about 3 ft into the tube, and how would you apply epoxy ? Would the epoxy be strong enough ? What happens when we need to replace the bearings in the future ?
SeahorseMarineDD54201 is offline   Reply With Quote
Old 09-08-2018, 09:44 AM   #137
Senior Member
 
Boat's Avatar
 
City: SchoolHouse Branch
Country: USA
Join Date: Jul 2018
Posts: 141
This is not meant to offend and I apologize if it sounds bad.


This problem has been ongoing for years?


Some things you make happen and some things you let happen.


Find the best shipyard you can find and the best vibration analysts you can find. Then everyone else involved needs to step aside and let them do their work.


On the other hand, that boat could make me happy sitting at the dock, without running.
Boat is offline   Reply With Quote
Old 09-12-2018, 09:22 AM   #138
Veteran Member
 
City: Zhuhai
Country: China
Join Date: Jun 2018
Posts: 66
Quote:
Originally Posted by Boat View Post
This is not meant to offend and I apologize if it sounds bad.


This problem has been ongoing for years?


Some things you make happen and some things you let happen.


Find the best shipyard you can find and the best vibration analysts you can find. Then everyone else involved needs to step aside and let them do their work.


On the other hand, that boat could make me happy sitting at the dock, without running.

Sorry for the late reply. All points of view welcome.
SeahorseMarineDD54201 is offline   Reply With Quote
Old 09-12-2018, 09:55 AM   #139
Guru
 
Join Date: Aug 2011
Posts: 577
I don't understand when you say all stern tubes have a built-in sag. That sounds like it would force a whip action between cutlass and support bearing(s).
__________________
TIME well wasted
1984 34' Mainship III
Arkan'tsaw
twiisted71 is offline   Reply With Quote
Old 09-13-2018, 08:25 AM   #140
Veteran Member
 
City: Zhuhai
Country: China
Join Date: Jun 2018
Posts: 66
Quote:
Originally Posted by twiisted71 View Post
I don't understand when you say all stern tubes have a built-in sag. That sounds like it would force a whip action between cutlass and support bearing(s).
I am saying this purely from a theoretical physics point of view.

As long as there is gravity, and the two ends of any Stern Tube are held up in the air, there will be a sag. Fiberglass Stern Tubes on long keels are typically aligned by centering the two ends of the Stern Tube, with the theoretical sag. Epoxy is then injected into the Shaft Log to fill the void between the Stern Tube and the Steel Shaft Log.

After the Stern Tube is aligned, the Whip Bearing is inserted about 1 meter into the Stern Tube where there is a sag. So even though the two ends of the Stern Tube may appear aligned, the section of 1 meter into the Stern Tube may not be, due to a sag.

One may argue if the two ends are axially aligned within a tolerance, the axial alignment at the middle section of the original molded Stern Tube cannot be worse. But if we ream the Stern Tube, the Reamer indexed to the sagged tube can make the misalignment worse. That's just my suspicion ...
__________________

SeahorseMarineDD54201 is offline   Reply With Quote
Reply

Tags
bill kimley, diesel duck, seahorse

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





All times are GMT -5. The time now is 03:09 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012