PDA

View Full Version : Bent propeller shaft!



PRB
June 7th, 2009, 14:07
Fliger (‘747’) Tom’s story about the “pounding decks” experienced when his destroyers were moving through the water at high speed reminded me of this experience.

When I first went to sea on USS Enterprise (CVN-65), the ship would shake when we were going “fast”. The shaking sensation was quite startling for a “noobie” like me. After all, the ship is 90,000 tons! I was amazed at how much the ship shook at high speed. What could be causing the severe shaking? Well, I was told that the ship had a “bent propeller shaft” and this was what was causing all the shaking. I didn’t quite buy that explanation, but I let it go. After all, what the heck do I know about propeller shafts and marine engineering? Over the next couple years and two deployments on the “Big-E”, the shaking at high speeds never went away. I guess they just never got around to straightening out that bent propeller shaft!

In a bar in some foreign port, I spoke with a sailor from the USS Independence (CV-62). We were taking about how fast these ships went, and he told me that the “Indy” had a bent propeller shaft, and that the ship shook like hell when they went fast! Amazing!

A few years later I’m on USS Nimitz (CVN-68) and guess what … the ship shook like hell when we were going fast! You guessed it – It seems Nimitz has a bent propeller shaft too!

Of course none of these ships ever went to sea with a bent propeller shaft. Hundreds of thousands of shaft horsepower will do amazing things to any man-made object, no matter how big, and it’s impressive to experience! And it gets more impressive the deeper you go in the ship. The CPO mess on Nimitz was on the 3rd deck, pretty far down for us “brown-shoes”! Down there the deck heaved up and down like a small earthquake. Awesome power.

Collin
June 8th, 2009, 03:04
Hi Paul,

it can happen on some big ships from launch day.

The shaft is not one piece but has a coupling and if this is off centre by a couple of millimetres then the shakes appear at high speed.

Engineers hate running shafts like this at high speed as it will have an effect on the shaft glands and bearings which get badly worn and have to be replaced, which can mean a lovely swim in the bilges and a lot of "swabbing up".

regards Collin:ernae:

fliger747
June 10th, 2009, 21:08
Apparently it has to do with interference between the propeller disturbances. Several of the late USN Battleships had very serious issues, somewhat ameliorated by having (I could have this backwards) 5 blade screws outboard and 4 blade screws inboard. It was also an issue on some two shafted ships, causing severe issues with gunnery sighting at certain speed ranges. I don't recall this issue on the diesel powered DE, but then we only topped out at 21 knots....