Another Keel Failure

[flaming]

Ker 40 Showtime lost her keel on the delivery back from Hobart after the Sydney Hobart.

Designer clarifies cause of keel failure >> Scuttlebutt Sailing News

Jason Ker has not be backward about coming forward with his take on the incident, and clarifying that the keel fitted to Showtime was not his original design, or built to a method he regards as appropriate.

This one is going to run I think....

 

[[2068]]

Welding the lower section to a horizontal T-Piece attached to the bottom of the boat looks like a very poor aftermarket design.

 

[bbg]

Ker 40 Showtime lost her keel on the delivery back from Hobart after the Sydney Hobart.

Designer clarifies cause of keel failure >> Scuttlebutt Sailing News

Jason Ker has not be backward about coming forward with his take on the incident, and clarifying that the keel fitted to Showtime was not his original design, or built to a method he regards as appropriate.

This one is going to run I think....

Lucky there was no loss of life. The keel design sounds pretty sketchy.

 

[lw395]

Lots of things are built by welding parts together in quite similar ways.
Welding is established engineering.
The question is, why did it fail?
Quality of weld?
Design? I,e, stresses not sufficiently understood and a perfect weld would not have been strong enough?
Stresses beyond the design envelope? e.g. impact from hitting the seabed, a whale, flotsam etc?

 

[anoccasionalyachtsman]

Lots of things are built by welding parts together in quite similar ways.
Welding is established engineering.
The question is, why did it fail?
Quality of weld?
Design? I,e, stresses not sufficiently understood and a perfect weld would not have been strong enough?
Stresses beyond the design envelope? e.g. impact from hitting the seabed, a whale, flotsam etc?

It sounds horribly like the welds were the hinge around which the keel wanted to swing, and that's never a great idea.

 

[Birdseye]

Lots of things are built by welding parts together in quite similar ways.
Welding is established engineering.
The question is, why did it fail?
Quality of weld?
Design? I,e, stresses not sufficiently understood and a perfect weld would not have been strong enough?
Stresses beyond the design envelope? e.g. impact from hitting the seabed, a whale, flotsam etc?

Quite right. Bridges, ships, cars are all built with welds. Its a design issue or maybe a quality issue - nothing wrong with the idea of welding the keel

 

[flaming]

Quite right. Bridges, ships, cars are all built with welds. Its a design issue or maybe a quality issue - nothing wrong with the idea of welding the keel

It always seems to me to be generally bad engineering to design something so crucial as a keel and then to rely on a welded joint at exactly the point in the structure that is under the most load.

Putting a type of join that it is very difficult to be entirely sure about in such a highly loaded and safety critical part of the structure simply looks like poor design.

 

[Motor_Sailor]

It always seems to me to be generally bad engineering to design something so crucial as a keel and then to rely on a welded joint at exactly the point in the structure that is under the most load.

Well that's how every metal boat has it's keel attached, whereas the vast majority of 'other boats' have their keels attached in pretty much the same area, by a row of bolts.

Whilst there are ways of attaching a high aspect fabricated keel with greater redundancy, it is possible with the arrangement as used in this case. But just as with so many other keel failures, there has to be more to it. Sadly, not every part of the boatbuilding world has adjusted to the rigorous methodology needed in the production of these keels, irrespective of their design.

 

[anoccasionalyachtsman]

Well that's how every metal boat has it's keel attached,

The difference is the relative thickness of the fins. When the boat's heeled - if it's thin then the weld is effectively a hinge, not good practice. If it's thick, the weld on one side weld is in compression, the other in tension, and that's fine.

 

[flaming]

Well that's how every metal boat has it's keel attached, whereas the vast majority of 'other boats' have their keels attached in pretty much the same area, by a row of bolts.

Whilst there are ways of attaching a high aspect fabricated keel with greater redundancy, it is possible with the arrangement as used in this case. But just as with so many other keel failures, there has to be more to it. Sadly, not every part of the boatbuilding world has adjusted to the rigorous methodology needed in the production of these keels, irrespective of their design.

There is a very big difference between the keel on a typical steel build, and a very high aspect keel dangling several tonnes of lead on a 3.5m long arm. Not only are the loads massively increased, but the area of the weld is a lot smaller.

 

[Motor_Sailor]

Show me a keel section that is so thin it would act as a hinge, apart from some cheap 1960's triple keel cobbled together job. Reductio ad absurdum.

All keels have to have sufficient cross section to be stiff enough and to function hydrodynamically. There will always be elements in compression and some in tension.

 

[Motor_Sailor]

There is a very big difference between the keel on a typical steel build,

Steel built? I said metal. We've done plenty of high aspect welded keels on aluminium raceboats and super yachts over the last 40 years. None fell off.
Also done plenty of welded steel foil sections for both bolted fins and canting keels.

 

[flaming]

Steel built? I said metal. We've done plenty of high aspect welded keels on aluminium raceboats and super yachts over the last 40 years. None fell off.
Also done plenty of welded steel foil sections for both bolted fins and canting keels.

Fair enough.
It's certainly not a method of construction that I would be comfortable having underneath me on a fin that high aspect though.

 

[Motor_Sailor]

It's certainly not a method of construction that I would be comfortable having underneath me on a fin that high aspect though.

As lots of structural components on boats move from being empirical designs that evolved over time, you better hope that they were designed properly, built competently and well maintained.

Of these, I've seen poor build standards and inadequate maintenance being more commonly the problem rather than poor engineering design. As lots of MAIB reports show, it's very hard for sailors to really know how well critical components will perform. This keel in question didn't fail because of the position of that weld. It was either underspecified, poorly built or loaded way beyond it's design parameters. A keel attachment design like Havoc V might have avoided all the so called short comings of this design, but its own litergy of manufacturing problems resulted in it being no more reliable.

 

[lw395]

In the limit, deep, high aspect keels are prone to getting broken.
The only question becomes how much hull will go with the keel.
It's a racing boat, something got broken, the hull stayed intact, nobody died.

The question is perhaps, was the weld strong enough, did it fail through abuse?
If the weld was not strong enough, it's a QA problem.
Not only is it impossible to make everything indestructible, it's not always a good thing.
Had the keel been strong enough to rip the hull open without falling off, it might have sunk in seconds with all hands.

 

[flaming]

As lots of structural components on boats move from being empirical designs that evolved over time, you better hope that they were designed properly, built competently and well maintained.

Indeed. There probably isn't a single part quite a critical as the join of keel to hull though.

Of these, I've seen poor build standards and inadequate maintenance being more commonly the problem rather than poor engineering design. As lots of MAIB reports show, it's very hard for sailors to really know how well critical components will perform. This keel in question didn't fail because of the position of that weld. It was either underspecified, poorly built or loaded way beyond it's design parameters. A keel attachment design like Havoc V might have avoided all the so called short comings of this design, but its own litergy of manufacturing problems resulted in it being no more reliable.

My point is more that putting a weld in that position puts the whole security of the keel to hull join onto a type of fixing that it is possible to get wrong without it necessarily being obvious that you have done so.

Unless the boat is ever recovered I don't suppose we'll ever know if the issue here was one of design or weld integrity. Don't accept that loading beyond design parameters is a possibility here, it was sailing, that's what it's supposed to do....

Haven't heard of Havoc V... Do you mean Hooligan V?

 

[Motor_Sailor]

Haven't heard of Havoc V... Do you mean Hooligan V?

Yes, brain fading.

I think you need to buy a J/125, purely for your peace of mind.

 

[flaming]

Yes, brain fading.

I think you need to buy a J/125, purely for your peace of mind.

Fabulous boats... Somewhat out of my price range though....

 

[lw395]

..... Don't accept that loading beyond design parameters is a possibility here, it was sailing, that's what it's supposed to do....
..

Cheeki Rafiki was sailing when it broke.
This boat may have hit something (other than water).

 

[flaming]

Cheeki Rafiki was sailing when it broke.
This boat may have hit something (other than water).

It might have done, but it's being reported that it hadn't.