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Posted by Tug Boat Lonnie on Wednesday, January 22, 2003 at 9:24PM :

In Reply to: Lonnie, I am Wondering..... posted by Paul (in NY) on Wednesday, January 22, 2003 at 6:52PM :

The tail shaft of a ship is actually tapered. The propeller has a matching tapered bore. The propeller and tailshaft have a keyway machined into them. The propeller is put on the tailshaft and the keyway aligned. The key is then inserted.

The end of the tailshaft is threaded to accept one very large nut. This is a fine thread which makes it critical to get it on right the first time and avoid cross threading the nut. The nut can weigh up to 600 lbs. It is held up by crane supporting a sling attached to a roller. This allows the nut to turn while the weight remains supported by the crane. The nut is carefully turned until the threads catch. The crane gradually releases weight as the nut is threaded on by hand. Once the nut is too tight to roll by hand, the crane comes back with a wrench. The wrench is a hand-made box end that can weigh several hundred pounds. The wrench is fitted on the nut and the crane pulls on a shackle fitted on the end of the wrench. The wing-wall crane we used was rated at 45 tons. When the wrench can no longer be pulled by the crane, the crane holds a strain on the wrench while we beat on it with a 20 lbs hammer. If the nut was tight, the wrench it would “sing” when we hit it.

Now a bullet shaped cone (usually made of fiberglass) was bolted on to the propeller. This encased the nut. A fill hole at the top of the cone was opened up and heated tallow was poured into the cone. When the cone was full (30 - 50 gallons) the fill plug was put back in. This bullet shaped cone is what most people see when the propellor is exposed on a ship. They don’t realize that one nut inside it is holding the whole shebang together.

Yes, you will occasionally hear of a ship whose propeller has fallen off. It happens but it is quite rare.

I have seen one cross threaded tail shaft. The ship spent an extra month in dry dock while the mess was sorted out.

Hope this answers you question. Sorry for the mispellings and band-width

Best Wishes
Lonnie



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