From: Mil-Veh Co. (milveh@sbcglobal.net)
Date: Mon Apr 25 2005 - 00:36:59 PDT
I believe the shafts are considered rebuilt when they
are cleaned, checked for true and for metal fatigue,
then balanced and the bearing surfaces are turned.
Sometimes they are sprayed with molten metal on the
bearing surface and then turned. No small feat on a
1000-2000+ lb. shaft, but its been 30 years since I
had a class in that, so they might do a lot more
now...I dunno.
Ship shafts (say that 10 times real fast) have one
problem area where the shaft passes thru the hull.
This is typically where you might find a thrust block.
The thrust area is usually controlled by some modern
version of an old "Kingsbury" type bearing with
collars holders that are rigid mounted to the hull and
this is what gets rebuilt in port..expensive.
On older vessels this can also be a thrust bearing in
conjunction with an "iron wood" bushing type bearing
which doubles as a seal, cheaper.
In the more modern version there is several composite
seals and a soft metal bushing which is designed to
wear out at the same rate as the thrust bearings,
which is ok because its saving the shaft bearing
surface which is harder and expensive to fix.
If the drive shaft is pretty long, say 1' wide shaft
that is more than 10' long, then that would require an
additional support bearing to handle the vibration,
torque and keep the shaft from warping at rest,
another additional cost too.
Those support bearing points almost never wear out and
long as they are greased...thrust bearings wear out oh
around 6000-10,000 hours on avearge depending on the
type of vessel and power. On the real large ships the
shafts must be rotated even while in port to keep them
from warping.
I'll bet you can get the props and shafts cleaned,
balanced, trued and surfaced for well under 25k...IF
you are at the right ship yard.
So who wants to sign up for the black gang (engine
room for you landlubbers)?
....Bridge to Mr. Scott, we need MORE power, now
Scotty! Aye Capt., I'm given er all she's got and if
I give er any more she'll blow!
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