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Anonymous Poster #1

Shaft Alignment with Extensive Structure Work

05/26/2012 4:55 AM

I have a friend who is working on a naval vessel of 58 Meters length & beam 8 meters. Shaft length is 62 Ft overall, there are three intermediate shafts of 13 Ft, 13 Ft & tail shaft is 36 Ft. The dia of the two 13 Ft shafts is 4.7 in & 5 in respectively. Extensive rebuild structural work for re-lifing has been done including renewal of struts or "P" Brackets as they are called locally. Four shafts, two inner & two outer. The problem is is with the two outer shafts which have 3 "P" Brackets each.

Now the problem is that alignment was done using the piano wire. They started from the stern & proceeded inwards. When they reached the starboard gear box coupling they discovered that the wedge with the intermediate was .0056 in at the top & the gear box flange is .079in higher then the intermediate shaft. Similarly, when the same process was done on the port shaft they discovered that the wedge with the gear box coupling & intermediate shaft was 0.0154in at the top & the flange was 0.013in higher then the intermediate shaft. Engine length is 9.2 Ft mounted on rubber clad resilient mount

The question to all those experienced marine experts is:

a. Can they adjust these by shimming of the gear box & similar adjustment of the propulsion engine, which is on resilient mounts.

b. Will these adjustments have any effect on the performance of the engine & the vessel.

c. How much of correction is allowable

An early response will be appreciated. Thanks

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#1

Re: Shaft Alignment with Extensive Structure Work

05/26/2012 9:54 AM

Does your friend (I presume an engineer) know your asking a group of strangers how to put a naval vessel back together?

I think the navy would like to know of this question, they and their government are paying.

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#2

Re: Shaft Alignment with Extensive Structure Work

05/26/2012 11:53 AM

That's a long shaft. Vessels tend to move about, alignments change with every wave and swell. I would imagine flexibility would be necessary. Are there no rubber mounts or spacers in this setup besides the motor mounts? If you don't give this drive train some freedom, you risk snapping shafts at couplings, IMHO.

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#3

Re: Shaft Alignment with Extensive Structure Work

05/26/2012 4:50 PM

Does your friend not have a computer?

.0056 inch is not very much. (Don't know what that is in meters) Just hit it with a hammer.

Please tell us this is NOT a United States Navy vessel. Since we have no way of knowing where you are, how can we render an opinion? Based on the lack of detail given, I'd say go ahead and shim things or cut and re-weld the shaft supports.

You should really just scuttle the thing right now if you are going to ask strangers how to fix it.

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#4
In reply to #3

Re: Shaft Alignment with Extensive Structure Work

05/26/2012 7:29 PM

Definitely not Canadian. Our navy consist a few guys in canoes and a beaver!...it's so sad.

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#5

Re: Shaft Alignment with Extensive Structure Work

05/26/2012 8:13 PM

That is close enough to get the tail shafts in place and re-float the vessel. Very important to know that your vessel sitting on a dry-dock is not at rest. Final alignment from the tail shaft to the gearbox must (should) be accomplished while the vessel is afloat in sheltered water. This is in fact accomplished by moving the gear and engine... Typically on the vessels shaft or bearing drawings you will find min and max for alignment values. Once the vessel is afloat, you may find the intermediate bearings need no re-alignment, however it is not unheard of to need full re-alignment after a major dry-docking period.

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#6
In reply to #5

Re: Shaft Alignment with Extensive Structure Work

05/26/2012 8:29 PM

Sorry I forgot to mention the vessel should be carefully ballasted to its normal draft as well.

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