42 searay broken shaft

Maybe rephrase to "He was not aware of hitting anything."

Confusing..



Old shaft, previous un-known repairs, un-detected D bend, Blem since new, moon phase, unknown collision or a combination of the above.
A world of possibilities.

Sure would like some pictures of the fracture. We may be still guessing but pictures could help.

Hi,

Could be any number of reasons including a change in alignment that may be as a result of deterioration of mounts, worn bearings etc.

If it has failed in an area where they was a machining induced stress raiser ( sharp edge) there has been something that caused the stress to suddenly raise to failure in an 18yr old shaft that has not been previously damaged or over stressed.

I haven't seen a shaft break for no reason either. He could've hit something, had line wrapped around it, or the propellor could've been loose banging on the keyway (which would be my guess), or he hit something.

I think a propeller shaft must be the most abused and un-appreciated component of a ships drive line. And still continues to operate with minimum failures.
Can you imagine the environment, twisting/torque it delivers in both directions, electrolysis and fine vibrations they take?
Then damage, repairs, adjustments and they go some more.

It's rare, but It happens, on big & little boats, sometimes they go.

If it was a quality shaft to start with (most are), then age should not be a concern by itself. 18 years of electrolysis and vibrations can ad to its age and contribute to a failure.

If there was a manufacturing defect I'd expect it to show a lot earlier than 18 years. Electrolisis could be a culprit, but that will be readily apparent. More likely bad allignment took its toll or he hit something. This time of year, and especially after a storm there's a lot of stuff floating in the Delaware and Chesapeake Bays, and the rivers. I've been through the C&D when at either end you could walk for miles atop the floatsom. Many times I've felt that nasty bang, waited with my breath held for a few minutes feeling for vibration, and conitued on my way forgetting about it when everything felt fine. That doesn't mean there couldn't have been damage within the shaft that's even invisible from the outside. Just part of boating. However I'd take this opportunity to take a close look at the cutlass bearing, struts and the entire drive chain, as well as rechecking my allignment.

Hi,

While searching for a news article about a bulk carrier that cracked its Prop shaft when sailing with a full load off the W Coast of NZ in 2009 , I found this by Pascoe.

Marine Engines : Drive System Alignment by David Pascoe, Marine Surveyor

Very good article K1W1.

When a shaft fails (cracks, breaks) between the prop and the strut, I've seen where it's because the prop is not fully seated in the taper - over time the shaft end (including prop) could snap off completely - and you won't necessarily get any warning such as vibration. It's why I don't like to have divers change props in the water.

That brings up an interesting question and that is how often to have haul-outs. My Captains feel that one should do it more frequently than most do, just as a preventive measure in examining everything closely. Obviously the dockyard agrees with that, so can't use their opinion too much since they have a financial incentive. I'd be curious to hear others opinions and practices in that regard.

On a wood, aluminum, or steel yacht, I'd recommend annually.

On Fiberglass many do it annually, I stretch it to 18 months on a lot of them. Depends on how the current bottom paint is holding up, how much usage and how things were on the last haulout (cutlass bearings etc.), and if the boat is about to take a very long trip.....such as FL to NY etc. This is for South Florida.

What is the conversion between this figure and ft/lb or Nm?

I would imagine that en isn't the only thing being lightened with this little escapade.