Reply
 
Thread Tools Search this Thread Display Modes
 
Old 09-13-2018, 10:02 AM   #141
Senior Member
 
Boat's Avatar
 
City: SchoolHouse Branch
Country: USA
Join Date: Jul 2018
Posts: 117
By the same argument the reamer will sag also. Can't support it everywhere, all the time. Tolerances for everything.


Shipyards build boats with acceptable vibration levels on a regular basis. There is at least one boat like yours with acceptable levels. There is someone out there, not too far away, who can make this very simple.


There is someone here who posts a tagline that says something like:
Once you buy the boat you are only the caretaker for the next buyer.


You just get some time with the boat and your time is passing. You never get the time back. If what you want is elaborate theoretical diagnostics then that's good too. I can understand that and be happy for you.
__________________
Advertisement

Boat is offline   Reply With Quote
Old 09-13-2018, 12:11 PM   #142
Guru
 
Join Date: Aug 2011
Posts: 577
How long are your stern tubes? Just to make sure we're talking about the same thing....when you say stern tube, its the section of tube that the packing gland/stuffing box (traditional or dripless) attaches to, correct?
And on your boat does the cutlass bearing go in this tube or does your boat have a strut supporting the distal end of the shaft just ahead of the prop?

I'm just not able to picture in my head having a stern tube (aka Shaft log) so long that it needs a support bearing between the cutlass and stuffing box. How do you keep the water from ruining the support bearing. or are you using two cutlass bearings (one at the end and another farther forward?

Our shafts were never more than 6' long and we'd mark the shaft at 2' and 4', place supports under it at those points, shim those until best alignment of shaft and transmission flanges, f'glass or weld shaft log in place, slip cutlass bearing and surrounding tube onto shaft, fit up strut pieces and tack weld together, remove strut/cutlass assembly, remove cutlass and finish weld strut assy and reinstall. We only had to install a support bearing once on a boat that had a 1.25" shaft. Our 2" shafts never needed a support/whip bearing. The support bearing though was forward of the stuffing box and was a simple pillow block bearing mounted to a stainless crossmember between the stringers.
__________________

__________________
TIME well wasted
1984 34' Mainship III
Arkan'tsaw
twiisted71 is offline   Reply With Quote
Old 09-13-2018, 01:35 PM   #143
Senior Member
 
BIG CAT's Avatar
 
City: Biloxi,MS
Country: USA
Join Date: May 2016
Posts: 286
Quote:
Originally Posted by SeahorseMarineDD54201 View Post
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 ...

I agree that a tube can sag of deflect under its own weight. but with a short section of 4" heavy wall pipe its unlikely you would be able to measure a significant amount of sag. now if the pipe were 40 ft long and had no center support. you would probably able to see with the naked eye. if your tube is truly not straight. it would be my guess it was that way when installed.
BIG CAT is offline   Reply With Quote
Old 09-13-2018, 01:54 PM   #144
Guru
 
Join Date: Aug 2011
Posts: 577
Quote:
Originally Posted by BIG CAT View Post
I agree that a tube can sag of deflect under its own weight. but with a short section of 4" heavy wall pipe its unlikely you would be able to measure a significant amount of sag. now if the pipe were 40 ft long and had no center support. you would probably able to see with the naked eye. if the tube is out truly not straight. it would be my guess it was that way when installed.
That's what I was trying to get my head around. For a tube that diameter used as a stern tube/shaft log to bend it would have to be absurdly long. Or perhaps it was distorted during welding to the hull? But there again the only part that should be of critical alignment would be the last t8-10" where the cutlass bearing fits. The stuffing box alignment is VERY forgiving on the inboard end. The shaft:trans mating flanges not being true or the shaft being bent would be my first suspects, especially on a new build. On the far outside range of percentages it also could be a bad prop. Off center or off true bore or one or more blades not being symmetrical .

O.P. Have you pulled the prop off and spun the shaft up to see if it still vibrates/whips?
__________________
TIME well wasted
1984 34' Mainship III
Arkan'tsaw
twiisted71 is offline   Reply With Quote
Old 09-13-2018, 03:40 PM   #145
Guru
 
psneeld's Avatar
 
City: Avalon, NJ
Country: USA
Vessel Name: Freedom
Vessel Model: Albin 40
Join Date: Oct 2011
Posts: 17,862
This is a low speed boat.

The amount of sag in over engineered components should be minimal....certainly less than any close tolerances someone wants to force into the mix.

I am in the get a real good vibrational analysis done.,... to see where the true problem lies....

Then get someone that can coreect the problem with tolerances that no one can screw up in refit.
psneeld is online now   Reply With Quote
Old 09-17-2018, 08:00 AM   #146
Veteran Member
 
City: Zhuhai
Country: China
Join Date: Jun 2018
Posts: 66
Quote:
Originally Posted by twiisted71 View Post
How long are your stern tubes? Just to make sure we're talking about the same thing....when you say stern tube, its the section of tube that the packing gland/stuffing box (traditional or dripless) attaches to, correct?
And on your boat does the cutlass bearing go in this tube or does your boat have a strut supporting the distal end of the shaft just ahead of the prop?

I'm just not able to picture in my head having a stern tube (aka Shaft log) so long that it needs a support bearing between the cutlass and stuffing box. How do you keep the water from ruining the support bearing. or are you using two cutlass bearings (one at the end and another farther forward?

Our shafts were never more than 6' long and we'd mark the shaft at 2' and 4', place supports under it at those points, shim those until best alignment of shaft and transmission flanges, f'glass or weld shaft log in place, slip cutlass bearing and surrounding tube onto shaft, fit up strut pieces and tack weld together, remove strut/cutlass assembly, remove cutlass and finish weld strut assy and reinstall. We only had to install a support bearing once on a boat that had a 1.25" shaft. Our 2" shafts never needed a support/whip bearing. The support bearing though was forward of the stuffing box and was a simple pillow block bearing mounted to a stainless crossmember between the stringers.
Sorry for the late reply. Prepared for then survived the worst recorded typhoon in Hong Kong.

Post #127 has a diagram of the assembly. The Fiberglass Stern Tube is 3.34 meter (about 11 ft). The boat has a long keel so the entire Shaft Log/Stern Tube/Shaft is within the keel, except the two ends. The Stern Tube is epoxied within (and is not the same as) the steel Shaft log (Seahorse does not want the steel shaft log to be exposed to salt water), the Cutlass Bearing and Whip Bearing are placed inside the Stern Tube, then the Shaft rotates within the bearings. Yes, the Shaft Seal (PYI make, I believe) is fastened to the Stern Tube at engine end. As the boat has a long keel, there is no strut.

There is a water injection point on the Shaft Seal, to push water through the (forward) Whip Bearing, then the (prop end) Cutlass Bearing.

Not sure I fully understand your assembling procedure. It sounds like you align the shaft, then build in the surrounding structure. Seahorse aligns the Stern Tube, epoxy in place, then insert the shaft.
SeahorseMarineDD54201 is offline   Reply With Quote
Old 09-17-2018, 08:03 AM   #147
Veteran Member
 
City: Zhuhai
Country: China
Join Date: Jun 2018
Posts: 66
Quote:
Originally Posted by BIG CAT View Post
I agree that a tube can sag of deflect under its own weight. but with a short section of 4" heavy wall pipe its unlikely you would be able to measure a significant amount of sag. now if the pipe were 40 ft long and had no center support. you would probably able to see with the naked eye. if your tube is truly not straight. it would be my guess it was that way when installed.
Thanks for the comment. Very much appreciate the judgement by experience of what's likely or not, as I am not hands on and have no feel of what is theoretically possible vs practically probable. Your comment will help me look into the right area.
SeahorseMarineDD54201 is offline   Reply With Quote
Old 09-17-2018, 08:18 AM   #148
Veteran Member
 
City: Zhuhai
Country: China
Join Date: Jun 2018
Posts: 66
Quote:
Originally Posted by twiisted71 View Post
That's what I was trying to get my head around. For a tube that diameter used as a stern tube/shaft log to bend it would have to be absurdly long. Or perhaps it was distorted during welding to the hull? But there again the only part that should be of critical alignment would be the last t8-10" where the cutlass bearing fits. The stuffing box alignment is VERY forgiving on the inboard end. The shaft:trans mating flanges not being true or the shaft being bent would be my first suspects, especially on a new build. On the far outside range of percentages it also could be a bad prop. Off center or off true bore or one or more blades not being symmetrical .

O.P. Have you pulled the prop off and spun the shaft up to see if it still vibrates/whips?
Again thanks for the words of experience (see Post #147). Based on several comments, it sounds like sag in Stern Tube is unlikely to be the cause of vibration. Seahorse workers did check during alignment and would not have proceeded if there was any observable issue with Stern Tube alignment. The shaft was pulled and checked to be straight. The Gear Box flange and the Cardan Shaft alignment was checked.

At this point I believe replacing the shaft with a name brand and re-aligning the whole drive train (as planned by Seahorse) is the way to go. Preferably there should be a vibration analysis which Seahorse has decided against.
Since Seahorse undertakes to pay for all this work done in Hong Kong now (as Seahorse does not have the money to bring the boat back to China), I will follow their decision.

Now, lets see whether Seahorse fulfills its promise, and how well Seahorse can ream the Stern Tube, without worsening the alignment due to possibly the original sag.
SeahorseMarineDD54201 is offline   Reply With Quote
Old 09-17-2018, 08:20 AM   #149
Veteran Member
 
City: Zhuhai
Country: China
Join Date: Jun 2018
Posts: 66
Quote:
Originally Posted by psneeld View Post
This is a low speed boat.

The amount of sag in over engineered components should be minimal....certainly less than any close tolerances someone wants to force into the mix.

I am in the get a real good vibrational analysis done.,... to see where the true problem lies....

Then get someone that can coreect the problem with tolerances that no one can screw up in refit.
Thanks for the comment. Please see Post #148 for reply.
SeahorseMarineDD54201 is offline   Reply With Quote
Old 09-17-2018, 08:22 AM   #150
Guru
 
Join Date: Aug 2011
Posts: 577
Quote:
Originally Posted by SeahorseMarineDD54201 View Post
.

Not sure I fully understand your assembling procedure. It sounds like you align the shaft, then build in the surrounding structure.
That is exactly what I was getting at.

How do you keep the whip bearing (assuming a roller/ball type) bearing from being ruined by the salt water its running in? As most anyone can tell you, a worn "planetary" type bearing will cause/allow deflection due to its rolling components causing chatter as they momentarily bind against their housing, keepers, and each other.

How far ahead of the shaft seal is the transmission? or next support bearing if there is one?

As crummy as it sounds, it seems like a significantly larger diameter shaft is in your future. IF your shaft is true and your prop isn't the cause. Has anyone ever suggested inserting a cutlass bearing at the inboard end of the shaft log? If you have a water injection between it and the seal it will prevent premature wear.
__________________
TIME well wasted
1984 34' Mainship III
Arkan'tsaw
twiisted71 is offline   Reply With Quote
Old 09-17-2018, 08:27 AM   #151
Veteran Member
 
City: Zhuhai
Country: China
Join Date: Jun 2018
Posts: 66
Quote:
Originally Posted by Boat View Post
By the same argument the reamer will sag also. Can't support it everywhere, all the time. Tolerances for everything.


Shipyards build boats with acceptable vibration levels on a regular basis. There is at least one boat like yours with acceptable levels. There is someone out there, not too far away, who can make this very simple.


There is someone here who posts a tagline that says something like:
Once you buy the boat you are only the caretaker for the next buyer.


You just get some time with the boat and your time is passing. You never get the time back. If what you want is elaborate theoretical diagnostics then that's good too. I can understand that and be happy for you.

I'd like to be a Diesel Duck lifer until my time is up. Fixing this vibration has become my obsession, though that may not be shared by Seahorse.
SeahorseMarineDD54201 is offline   Reply With Quote
Old 09-17-2018, 09:12 AM   #152
Veteran Member
 
City: Zhuhai
Country: China
Join Date: Jun 2018
Posts: 66
Quote:
Originally Posted by twiisted71 View Post
That is exactly what I was getting at.

How do you keep the whip bearing (assuming a roller/ball type) bearing from being ruined by the salt water its running in? As most anyone can tell you, a worn "planetary" type bearing will cause/allow deflection due to its rolling components causing chatter as they momentarily bind against their housing, keepers, and each other.

How far ahead of the shaft seal is the transmission? or next support bearing if there is one?

As crummy as it sounds, it seems like a significantly larger diameter shaft is in your future. IF your shaft is true and your prop isn't the cause. Has anyone ever suggested inserting a cutlass bearing at the inboard end of the shaft log? If you have a water injection between it and the seal it will prevent premature wear.
You need to look at the diagram in Post #127.

The Whip Bearing is physically identical to the Cutlass Bearing, a Duramax water lubricated bearing, no balls. The shaft is supported by the Cutlass Bearing at Prop end, the Whip Bearing in the middle, and the Thrust Bearing (some would say it's a flange bearing) at the Gear Box end. The Thrust Bearing is a oil lubricated ball bearing. Presently the Whip Bearing is right in the middle between Cutlass Bearing and Thrust Bearing (1.8m from each), though in the past it was about 2' forward.
SeahorseMarineDD54201 is offline   Reply With Quote
Old 09-17-2018, 10:10 AM   #153
DDW
Senior Member
 
City: San Francisco
Country: USA
Join Date: Apr 2018
Posts: 318
An 11' fiberglass tube would definitely sag under it's own weight. Whether enough to be a concern I don't know. There is another possibility though: if it was supported at the ends and then epoxy injected into the void, it will be buoyant and will float, deflecting upwards. Which wins depends on the size, weight, epoxy density, etc.

As a machinist I can assure you that EVERYTHING sags or defects. Even heavy solid steel castings. Think of everything as being made of rubber - some of it stiffer rubber than others.
DDW is offline   Reply With Quote
Old 09-17-2018, 01:08 PM   #154
Guru
 
Join Date: Aug 2011
Posts: 577
Does it vibrate in reverse as well as forward?
__________________
TIME well wasted
1984 34' Mainship III
Arkan'tsaw
twiisted71 is offline   Reply With Quote
Old 09-18-2018, 07:45 PM   #155
Guru
 
City: NC
Country: US
Join Date: Jan 2014
Posts: 669
SeahorseMarineDD54201,

Did your boat do ok in the typhoon?

You might be also interested in the Dirona blog posts about their prop shaft vibration. They mentioned some information that might be helpful,https://mvdirona.com/2018/09/trondheim-projects/ and see the section on "Shaft Runout" There is a link in that discussion about their shaft vibration problems that started back in the UK.

Later,
Dan
dannc is offline   Reply With Quote
Old 09-30-2018, 05:40 AM   #156
Senior Member
 
Boat's Avatar
 
City: SchoolHouse Branch
Country: USA
Join Date: Jul 2018
Posts: 117
Hi. I did some more reading about your situation and for several reasons am now even more convinced that you need highly competent vibration analysis.

I looked at the sequence of pictures showing 55' Diesel Duck construction on the Diesel Duck website. I would not rule out the possibility that you have issues with the whole back end of the boat. The analysis needs to include the rudder, keel, prop, shaft and hull.

I also question the motivation for not returning your boat to the factory. There may be a question of leverage with legal jurisdictions, statute of limitations and other issues beside government policy with taxes or bonds or whatever. … Bad press, public scrutiny, conflicts with promoters, etc. Out of sight, out of mind.

Does an electronic model of your boat exist? The plans should be digitized on a computer somewhere and can be analyzed for strain and harmonic issues.

Somewhere, reasonably close to you, exists a team of naval architects, engineers and vibration analysts who can conclusively troubleshoot this.

Wishing you the best as another year quickly passes.
__________________

Boat 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 08:38 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