From: Fred Martin (mung@in-touch.net)
Date: Mon Apr 25 2005 - 11:54:15 PDT
As a former tender sailor....machinery repairman (machinist) I've had
some experience machining the thrust bearing surfaces...on a tincan
about 3' diameter....pretty good sized lathe required and a horizontal
boring mill to bore and cheek and oil groove the spring bearings that
support the shaft as it goes back thru the shaft alley. The thrust
bearings were segmented and there were several of them fitted around the
thrust surface of the shaft. Also the bearings had to be hand scraped to
fit the shaft with Prussian bluing and hand scrapers. Would also need
molders and pattern makers to make up the molds for the bearings and
pouring them and plenty of high speed babbit. If you can picture a
destroyer with it's wake behind it pushing the ship forward...it puts a
lot of push against the propellor shaft and it requires a lot of bearing
surface to handle it....and you can't forget to cut in the lube oil to
it as in one case I'm referring to. They court martialed the black gang
that forgot. Had to cut hatches and doorways just to get it out and over
on the tender. Took pictures of it after every move....even me as I
machined it and afterward when it was done. Fred Martin USS Arcadia
and USS Shenandoah....tenders.
Mil-Veh Co. wrote:
>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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