Carbon Mast Down -Poor Build.

[Llafurio]

Last weekend, in a Drascombe Rally, in brisk but not unusual conditions, I saw a BR20 carbon mast fall. I attach a photo (Credit: Paul M.). Have a guess what likely caused it.

Or, better, what would have prevented it.

[mark1]

I'm not sure! Is the mast UV damaged?

[Llafurio]

...Is the mast UV damaged?

Nope. The apparent lighter colour of the destroyed mast top is an effect of the destruction, not of a UV degradation. The breaking of an anthracite colour carbon mast leads to micro - delamination of matrix and fibres which shows up as greyish.
Guess on!
C.

[mark1]

oh ok, well is it the shape of the wood bung then?

[Ape Ears]

Compression from shroud / forestay / main halyard tension driving wooden bung down beyond rim like a wedge to cause top of mast to split catastrophically ?

More resistant design of top mast fitting could be engineered ?

Possible common alternative : failure to secure shroud shackle with cable tie or wire so it comes undone when you least expect it ?

[PYoung]

I had an unbelievable experience today. My BC23 was almost dismasted!

I was sailing in a lovely groove on a beam reach and all of a sudden my leeward shroud popped off the chain plate. Thankfully I wasn’t alone and it was the leeward shroud, or it could have been catastrophic!

I managed to run a bit of spare rope through the eye of the shroud and tension it enough to drop the main and motor on. As I was motoring I then discovered the pin in the other shackle of the windward shroud was free and had almost worked itself out.

I had been meaning to mouse all of the shackles, but I never got round to it. This has been a real wake up call for me and will be definitely looking into making my rigging more secure.

Scary stuff!

[Llafurio]

Compression from shroud / forestay / main halyard tension driving wooden bung down beyond rim like a wedge to cause top of mast to split catastrophically ?

: That is exactly what happened in the final moments. But there is craftmanship fail and fault development that led up to it.

More resistant design of top mast fitting could be engineered ?

: Yes. But wasn't. I suspect more boats have this faulty design of top mast fitting, and will suffer the same fate.
C.

[Graham W]

I had an unbelievable experience today. My BC23 was almost dismasted!

I was sailing in a lovely groove on a beam reach and all of a sudden my leeward shroud popped off the chain plate. Thankfully I wasn’t alone and it was the leeward shroud, or it could have been catastrophic!

I managed to run a bit of spare rope through the eye of the shroud and tension it enough to drop the main and motor on. As I was motoring I then discovered the pin in the other shackle of the windward shroud was free and had almost worked itself out.

I had been meaning to mouse all of the shackles, but I never got round to it. This has been a real wake up call for me and will be definitely looking into making my rigging more secure.

Scary stuff!

And this is what happens when the windward shroud shackle comes undone (warning - contains graphic content) https://www.swallowyachtsassociation.org/smf/index.php/topic,391.0.html

[Llafurio]

I have modified the title of this thread so not to mix up very different reasons for losing a mast, poor craftmanship by the yard, or poor seamanship by the owner. The two have nothing in common. C.

[Matthew P]

How much pre-tension was there on the shrouds?                                       

Was the downwind shroud slack when the mast failed?

Matthew
BR17 Tarika

[Llafurio]

C'mon, Matthew. What has the pre-tension got to do with a mast catastrophically failing in moderate conditions?
-You know how hard I pre-tension my own masts, I showed you once.
And btw, all BR lee shrouds go slack when the mainsheet is hauled hard.
C. 

[Nicky R]

I have modified the title of this thread so not to mix up very different reasons for losing a mast, poor craftmanship by the yard, or poor seamanship by the owner. The two have nothing in common. C.

We can add a third reason for losing a mast: equipment failure. We lost our mast a few years ago when the shackle on one of the shrouds failed. It failed by the round (unthreaded) eye and straightened the shackle. (The pin was still screwed firmly into the threaded end.) The nominal breaking strain of the shackle was twice that of the wire, so it wasn’t a break that could be anticipated or prevented. The mast was fine, but we needed a new tabernacle as the old one bent when the mast went over the side.

[Llafurio]

We can add a third reason for losing a mast: equipment failure. We lost our mast a few years ago when the shackle on one of the shrouds failed. It failed by the round (unthreaded) eye and straightened the shackle. (The pin was still screwed firmly into the threaded end.) The nominal breaking strain of the shackle was twice that of the wire, so it wasn’t a break that could be anticipated or prevented. ...

Not surprising. By what you write it was a stamped shackle, not recommended for high loads, and very likely the load on it was one-sidedly distributed, on the leg of the unthreaded boring, which already diminishes the theoretical official
breaking load.
Plus, there are really awful stamped shackles on the market, where the wholes are visibly not punched centric to the side lashes.

And, yet again, it comes down to the one question, was this a shackle of your own choosing, or did it come with the boat?

-To come back to the original mast failure, what do you think the yard did wrong there?

[Nicky R]

I’m not going to guess the cause of the failure. As an education researcher it's not exactly my area of knowledge.

According to my engineer husband, the failed shackle wasn’t a stamped one. He kept it because it was interesting! I don't know whether it was yard supplied or not as we bought the boat second hand.

[Graham W]

To come back to the original mast failure, what do you think the yard did wrong there?

Given the potential safety implications, I suggest that instead of playing guessing games you tell us what you know about the dismasting.  I’d rather hear an account directly from the poor BR20 owner but in his/her absence we’ll take your version.  I’ve also alerted the yard to this thread so that they can respond.