Was the Bayesian Design a deathtrap?

Bayesian death trap

Many years ago we built an ocean going catamaran. Thanks to Derek Kelsall an amazing boat designer.

At the time people would tell us that catamarans unlike mono-hulls were inherently unsafe. The theory being that if a catamaran capsizes, unlike monos, it will not self-right. In fact there was plenty of literature on the subject and it was always argued that a well designed mono-hull would right itself due to the weight of the keel which no matter what, even when the boat was full of water, would exert a downward force which would turn the boat upright again.

The Bayesian builder has issued a statement that she is stable up to 73° with the keel raised and 87.6° with the keel fully down.

Meaning if she lies on her side she should still not sink.

But that is as we now see a terrible risk. An ocean going boat must always be designed to go past 90°. For one it should never be assumed that if the boat is ever tipped over by an enormous wind that she will be sitting on perfectly level water. In fact when one puts a little thought into it, it is very unlikely.

How often have we been reminded that boats of any size can, through a combination of strong wind and enormous seas with huge waves be turned upside down.

Almost more shocking than the terrible stability mis-design is the fact that this boat sank so quickly. Most mono-hulls in the same situation could well turn upside.down and hopefully self-right. Even if this doesn't happen they should normally not sink.

One might remember the dreadful Fastnet race where the boat being sailed by Simon le Bon (Frontman with the group Duran Duran) ended up upside down with the crew inside. In that case the keel had broken off and so the boat could not self-right.

But even so, his boat did not sink. So one has to consider why this £14 million monster could fill with water within a few minutes and why it had no inherent buoyancy to keep it on the surface.

Looking back at the Fastnet race most of the boats that were severely damaged did not end up on the bottom of the sea.

But Andrea Ratti, a nautical design professor at Polytechnic University of Milan, said a boat the size of the Bayesian could only sink so rapidly by taking in a huge amount of water.

A rubbish statement: Tom Sharpe, a retired Royal Navy commander and defence commentator, told CBC News that a mast the size of the Bayesian's is designed for a massive sail, and without that sail raised and catching the wind, the gusts likely would've had a negligible impact on the aluminum pole.

The hull is aluminium and has therefore no inherent buoyancy. Probably most normal sized yachts nowadays are built with glass fibre and in many cases are double walled with a type of sandwich construction. This means that even if the boat fills completely with water it will still float.

Looking at photos from the interior it seems fairly apparent that a very open plan design was used. Again this means there are no spaces which would retain enough air to provide buoyancy.

The Bayesian superyacht was "virtually unsinkable", the chief executive of the firm that built it has claimed. Titanic et al? Or pride comes before the fall?

Dimensions

Aluminium Hull, Mast 72m, in some reports 75 meters or 72.3 as the total height above the waterline.

Length 56meters

Cruising speed 12 Knots but also 14.7 quoted

Draft max 10meters with keel down and minimum 4meters when raised

Displacement 543 Tons

Reports

The chief executive of the firm that built the Bayesian superyacht has claimed the crew would have had time to avert disaster.

Giovanni Costantino, who leads the Italian Sea Group, suggested the doors of the vessel may have been left open during the freak tornado that hit the yacht on Monday morning.

Costantino said that the vessel was "like a pendulum" and designed to return upright even when tilted at an angle of 87.6 degrees, almost horizontal. "That's if there is no water inside the yacht, but I suspect there was" Costantino said.

"I have studied the tracking data which shows that at 3.50am on Monday, when it was at anchor, it moved 400 metres in four minutes, probably dragging the anchor and likely taking on water".

Commenting on speculation the crew raised the yacht's keel, rendering it less stable, he said: "I don't see that as a factor since even when it's up, the yacht can lean over at 73 degrees and still right itself". He also suggested the crew should have gathered the passengers at an assembly point.

One last completely different thought. Once when I was talking to Derek Kelsall about the problems of capsizing he told me that in his experience cats often do not tip over sideways as one might assume, but they bury one hull under a wave and do a sort of diagonal cartwheel.

With Bayesian and her huge mast it is actually quite easy to imagine that using the mast as a gigantic lever she could have buried her bows into the sea and then shot down into the depths. If, but again, this is pure speculation she was gyrating around on or rather over her anchor chain, as the data from AIS suggests, imagine she has run over the anchor and it now starts pulling her bows down, add the fulcrum of the mast and it seems quite possible.

-pw- London