Why would a mast, just fall down?

[Sans Bateau]

Friend visiting us this weekend was all fed up. Turns out the mast on their wooden Folkboat fell down. The curious thing is the boat was on it's swinging mooring at the time.

Apparently the Seldon mast has recently been resteped after a refit, the boat was then sailed without any problem twice. When the boat was then revisited after some boisterous weather, the mast was found hanging by its shrouds in the sea! The mast itself was broken about 20 - 30cm from the base, non of the shrouds were broken. The one theory that has been suggested is that the split pins may not have been in the bottom of the bottle screws, allowing them to undo(??). I dont mean the split pins in the clevis pins either, that I could understand. This theory seems a bit strange to me, how could they just unscrew when they are under tension?

I do have a theory oif my own, but any ideas from you guys?

 

[PeteCooper]

Bottle screws can undo on their own when not prevented by a split pin - Ive seen it happen. I would imagine it is vibration that does it but that's only a guess.

 

[sailorman]

[This theory seems a bit strange to me, how could they just unscrew when they are under tension?]

did the wires streach allowing the deck stepped mast foot coming adrift from the mast shoe

 

[Sans Bateau]

Mmm, the rigging was not new, the original rigging just put back, it was only three years old.

The boat, as I said, is kept on a swigging mooring, I suspect that during this period of strong winds the wind against an ebb tide would have kicked up a bit. The boat with its long keel would try to sit to current, but a strong wind on an empty boat (lightish) would swing it around to put the flow of the ebb and the swell beam on. This would have the effect of the boat rolling violently from side to side.

Question is, would that be enough to break the bottom of the mast?

 

[Sans Bateau]

I can't remember, bottle screws have a lock nut as well dont they?

 

[lw395]

Sounds very odd.
Suggest looking at the break. Is it corrosion? Damage while ashore?
At first I took your post to say mast was new, assume not?
Odd place to break, stress is generally more at gooseneck level, unless there is some fitting I'm not aware of.
Am I right in thinking its a deck-stepped mast?
Unless the bottle screws came completely apart, I would expect the mast to stay up. Even the loss of one shroud should not be a problem with no sails up, unless there is a lot of pre-load involved.
I would want to talk to a rigger or the mast manufacturer.
Are ther any signs that someone has collided with the boat/rig?
Commiserations!

 

[Sans Bateau]

Your right in your assumptions.

Deck stepped
Not new

The rig is fractional, aft swept spreaders, upper shrouds and lowers just below the spreaders.

If though the bottle screws did come lose, the violent rolling I suspect, that might be enough. The boat had in a past life been raced, I have not seen the mast yet, but I would not be surprised to see corrosion or cracking that produced the break.

Collision is an interesting thought that did cross my mind, again I still await to see the boat.

 

[Seagreen]

Thats a very odd break. If non of the bottlescrew assemblies came undone, and I think it would have to be a very violent collision to cause that amount of damage, the hull would be seriously damaged. All that remains is corrosion or some flaw in the metal of the mast. I presume its still under warranty?

 

[Sans Bateau]

Its not a new mast, the mast is old.

 

[Pye_End]

[ QUOTE ]
I can't remember, bottle screws have a lock nut as well dont they?

[/ QUOTE ]

The only rigging screws I have had have either been open bodied or have locking nuts (don't like these) - but not both.

 

[Graham66]

My thinking would be that the forestay would have become detached first either by a nut slackening or a split pin falling out caused by vibration or mooring cable interfering with rigging screw when shearing about (I have seen that happen many times on moored vessels) then it wouldnt take a lot for the other rigging to slacken brought about by the whip of the mast.
it only needs to be minimal to allow the mast foot to displace and then the mast will come down.

 

[BAtoo]

I would suspect a rigging screw coming un-done allowing movement etc.

Happened on my Squib's forestay, fortunately with no damage as the mast is keel-stepped. This was following some quite heavy weather and I suspect the screw had worked itself undone - I possibly hadn't tightened the locking nut enough. /forums/images/graemlins/blush.gif /forums/images/graemlins/blush.gif

 

[Salty John]

If the rigging screws have been tightened but not pinned they will tend to unscrew themselves. This is because as you tighten a rigging screw you are tending to twist the shroud - like tightening the rubber band by turning the prop on a model plane. The 'memory' built up in the shroud will cause it to unscrew again; once loose, vibration takes over and completes the job.
I once fitted a new rigging screw, tensioned it but didn't secure it. The next day it had completely unscrewed itself!
I'd guess that's what happened in this case.

 

[MasterofHera]

When was the preebend put in? If it was after tensioning of the rig it may have over stressed the mast at an already weakened point.I always recheck my tension after putting in the prebend on my FB.

 

[peterb]

It's a funny place to break. The break would mean that the mast was under stress; compression, tension or bending. Very unlikely to be tension; compression usually involves buckling, which usually happens in the middle of an unsupported section; most likely to be bending. But bending means that the sections above and below the break are restrained in such a way as to provide a bending moment, and usually a deck-stepped mast is free to move at its deck step; unless, of course, there has been a high sideways loading near the fracture point with the heel restrained from sideways movement.

Were there any holes for fittings at the level of the break? Could it be a fatigue fracture, ending with buckling under compression? Pictures of the break could be interesting..

 

[Sans Bateau]

I have yet to see the mast/boat, but hope to soon. It will no doubt help the explanation

 

[chewi]

My mast did not collapse like that, but in a collision with another boat the lower shroudswere caught and pulled the mast down which buckled the lower section. If there were a collision like that at the mooring the failure might be at mast gate, gooseneck etc , not necessarily halfway, but then the bottlescrews would not be undone.

 

[richardblake]

If the mast was stepped as you say by a yard I am sure they would have wound the bottle screws up evenly and thus not allowing the shroud to twist up. I would guess that the mast was weakend at sometime in the area that fractured and the final cause for breaking was due to a collision of some kind. If it is due to loose shrouds the break should show clear signs of fatigue failure. At the end of the day until you see it we can all keep on guessing.