Bruce Farr Design ruins Beneteau First reputation

[lw395]

I am no engineer.

But I guess the internal liner is there to distribute keel loads into the hull and add rigidity. If it becomes detached or damaged it no longer does it's job and the loads go elsewhere. I assume this would be into the keel area which is not designed for the job, the subsequent lack of rigidity allows the structure to move, a bit. Once the compressive strength of the fibre is is exceeded it can move a little more and leak. Once the keel can move freely, at sea, all bets are off. The only question is: will the bolts or the structure fail first? In this case it seems to be a little of both.

Is that daft? Or what.

How do you mean 'is that daft?'

Things break when you crash them into hard things.
Broken things sometimes don't work.
Broken things that have not been repaired right sometimes break again when given a hard time.
Some broken things are hard to repair and very hard indeed to check whether the repair is good enough.

An atlantic storm requires a yacht to be properly strong.

 

[doug748]

How do you mean 'is that daft?'

What I mean is:

As an account of how the failure occurred, by a non engineer, is it a plausible alternative to the suggestion by Yara (who is an engineer) that:

"It is clear that the initial failure was precipitated by failure of some of the bolts themselves, rather than the structure"


Is that daft? - Is an invitation for others to agree, pick holes in the theory or maybe support Yara.

 

[Yara]

I suspect the above analysis may be deeply flawed.
A reduction in the strength of the hull laminate would cause the loads not to be distributed properly, overloading each keel bolt in turn.

Analysis by analogy to fish cans and a disdain for computers sounds OK in the bar, but probably misses the point.

The keel bolts hold the matrix to the hull, so the shear strength, not the adhesion is what counts. Failure of the matrix bond would cause hull flexure and damage away from the keel area, and none was visible.

 

[Yara]

The central point of his post:
""It is clear that the initial failure was precipitated by failure of some of the bolts themselves, rather than the structure.""

That's not actually clear at all is it?
Failure of the bolts would probably be a quick process, not involving a day of leaking.

Crevice corrosion can be slow, and failure of the outer central bolts could indeed cause slow leaks if they have failed. As built, the design is strong enough, so something would have had to fail first to start the process. The corrosion stains point to bolt failure.

 

[lw395]

Crevice corrosion can be slow, and failure of the outer central bolts could indeed cause slow leaks if they have failed. As built, the design is strong enough, so something would have had to fail first to start the process. The corrosion stains point to bolt failure.

We know the boat was grounded previously.
There is only serious staining around one bolt, the aft one.

You agree it was built strong enough?

 

[lw395]

The keel bolts hold the matrix to the hull, so the shear strength, not the adhesion is what counts. Failure of the matrix bond would cause hull flexure and damage away from the keel area, and none was visible.

There were bits of laminate missing outside the area of the keel chord, that is flexure and damage in my book.

 

[LittleWings]

The central point of his post:
""It is clear that the initial failure was precipitated by failure of some of the bolts themselves, rather than the structure.""

...actually i do agree: once the structure is torn it is unlikely for the studs to snap.

 

[30boat]

...actually i do agree: once the structure is torn it is unlikely for the studs to snap.

And it apears the studs were doing their job as they took some laminate with them.

 

[LittleWings]

iirc there was a pica of snapped ones

 

[Sailfree]

The central point of his post:
""It is clear that the initial failure was precipitated by failure of some of the bolts themselves, rather than the structure.""

That's not actually clear at all is it?
Failure of the bolts would probably be a quick process, not involving a day of leaking.

Comes down to semantics. The keel bolts failed most likely initially one at a time then progressively. Whether it was the bolt material or the matrix it was securing it still amounts to a failure of a bolted keel attachment method.

I could envisage a possible mode of failure of an intitial bolt causing extra stress on the others causing a slow leak that would get worse if the keel was "working".

As such no one can be sure of the failure mode and all contributions give rise to consideration and many add to others knowledge.

 

[grumpy_o_g]

Without knowing what force was applied and when and where any attempt at analysis is pretty pointless. What CR has done is bought to our attention the fact that we don;t really check very thoroughly for any warning signs of earlier damage and that, even if we wanted to, we aren't sure how to. That's the lesson to be learnt and worked on going forwards.