How does a propeller "fall off"?

I’ve seen something like that before, presumed due to failure of continuity brushes and cavitation damage to the coating on the stainless rudder. It led to fire hose level stern gland leakage long before anything broke.

As for the general question, most prop losses I’ve been involved with were thought to be due to installation error. That’s in the wonderful world of small craft, with a much higher incidence of unqualified yard hands kludging mission critical systems.

I’ve seen two unexplained deep water shaft failures as pictured above. I was told that the likely culprit was propeller imbalance, so thanks @freighterman1 for widening the picture. The progressive nature of the crack was highly evident due to gunk having established itself in the older part.

Large Azipod units have built-up propellers so there’s also the possibility of throwing a blade rather than losing the whole propeller. That would explain the sound - the propeller as a whole would not be “hurled up” by the shaft rotation.

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I remember dealing with an intermediate shaft that fractured through just aft of the flywheel on a tanker, back in the 90s. It was hush-hush at the time, since it was apparently not an unusual even on this particular class of ship, that had a lube oil pump driven off of the intermediate shaft.

Back to the Norwegian Jewell and the Azipods she is equipped with:
https://new.abb.com/marine/systems-and-solutions/azipod
She has 2 X 19.5 kW nacells driving fixed pitch propellers.

Thanks. Reports from passengers said the ship was reduced from 20 to 16 knots as a result. If the whole propeller fell off I guess she could continue without too much problem on the other one, but if a single blade broke off and the ship was still capable of doing 16 kts that would put a whole lot of stress on the unserviceable azipod and an unbalanced prop if still trailing. Not likely?

Easy. After a week of shrimping in the Gulf, pull in to the fish house pier at Key West. While waiting in line to unload throw the nets over the outboard side to soak.
When the word comes to move up the line start the engine and…oops. Prop’s in the mud.
F/V Mr. Gardner, Key West, 1980.

Well at least it was where you could find it!

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True.

Until I hear something from someone besides a passenger that anything actually fell off, I find it hard to believe. Their plan was to make repairs in Honolulu Harbor and said it could only be done without passengers onboard. Is there a dry dock large enough there, or could this be related to the power side of things?

But 16kts trailing would definitely be stressful. At least with nozzled azi thrusters you can turn them sideways and lock them if you’re not going too fast. I’m sure you can lock the prop there, but trailing with a blade missing would be like driving with the worst unbalanced tire ever. Your bearings would hate you.

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This!

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How the French Navy handled a propeller loss:
On her last sea trial, underway to Norfolk VA, the new (in service 2001) and only nuclear carrier ‘Charles de Gaulle’ lost a blade of the port propeller.

They determined a foundry error with the cooling sequence from liquid to solid of the copper-aluminium alloy. The carrier’s second propeller had the same error, as had the third spare propeller.

After that, unfortunately (?) the French foundry’s archive burned down. All drawings, specifications, calculations and production protocols went up in smoke.
Neither the Navy nor another administration found copies of these documents…

Two spare propellers of the old conventional carriers ‘Foch’ and ‘Clemenceau’ (both disarmed, then) were fitted. As suspected, the carrier’s maximum speed was 25 instead of 27 knots. That did not allow the use of their fighters ‘Raffale’ under all weather conditions.

An American foundry of Rolls Royce Marine made new propellers…

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Here is the unit:

I found it hard to believe too. It hadn’t been mentioned in this site (and that surprised me) and I simply read it in one of the links at my first post. The passenger simply wrote amongst a general litany of bad luck that the final straw was “a propeller fell off” and consequently the ship slowed down, further delaying it and complicating exactly where in the world the passengers would eventually be allowed to disembark.

The company is obviously embarrassed. They’ve said nothing that I can find. I’d love some official confirmation. Photos would be great.

Heres some pics from the Norwegian Star back in the day at a dry-docking, which I believe uses the same units on the Jewel. Don’t bother to tell me I look badass in a muscle shirt, I already know. haha

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Was working on the tug Geronimo back in the late ‘80s when we developed a bad vibration, pulled into Portland and a diver verified that we lost a blade off of our wheel, fixed wheel

I remember the old training ship had a spare prop blade bolted down back aft. I could never figure out the scenario were we’d need just the one blade. I guess that’d be it!

Pretty common on a CPP setup to have one blade have an issue. Certain CPP hubs are relatively simple (strong relatively) to replace a blade in the water on.

Makes sense for CPP. On the 1000 ft lakers we could ballast down the bow and just get the upper half of the wheel and the CPP hub out of the water. Pretty convenient for inspection. That old steamer training ship sure wasn’t CPP though :smile:

I once saw a photograph of a Russian icebreaker that had returned to port with a total seven blades left on its three four-bladed propellers…

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I once “developed a problem” with a cpp blade (backed right into a bump in the harbor sole) so deep in the boonies that it took the better part of a week to find a yard with the capacity to lift us out. It wasn’t exactly a fun time, listening to every loose object on board rattling around while we fought the current.

When I finally got a good look, it turned out that the screw was hand made in some shed in a tiny village, the guy who made it was long dead, and there was zero chance of finding a replacement. I ended up fixing it the crude way:

I figured I was pretty much scrapping the screw, but it was already getting loose, and with no parts available and an immediate need to do something about the vibrations before cracking the hull, I went ahead to much eye rolling from the yard hands. Amazingly, I came out of it no worse than before the ground strike, and later had it reconditioned by a machine shop.