yacht sunk in med

Lynch’s superyacht sank because of ultra-tall mast, says rescue skipper
An experienced boat captain whose ship was anchored close to Mike Lynch’s superyacht when it sank in a violent storm off the coast of Sicily on Monday has said the stricken vessel appeared to capsize because of its extremely high mast.
“In my opinion there is something wrong with the stability,” Dutch skipper Karsten Börner told the FT about the sinking of the 540-tonne Bayesian, which caused the deaths of the UK technology entrepreneur and six others, including Lynch’s daughter.
“The centre of gravity is too high with this extreme mast,” said Börner, referring to the tallest aluminium boat mast in the world.
He rejected an initial assessment by the Italian coastguard that Bayesian was “in the wrong spot at the wrong time”. He said: “I was on the same spot. I have two masts and they are 28 and 29 metres above deck, she has one, 73 metres above deck.”Subscribe to read https://www.ft.com/content/551b0b6d-2121-4d63-9563-dcd67722c1e0

 

(1) 56m luxury sailing yacht sinks off Sicily, 7 missing | Page 69 | Sailing Anarchy Forums

 

"Far from unsinkable, as the builders claim: the Bayesian was a boat that was too 'pushed' and in some way cursed, which did not really have to sail, built to show off endless luxury but made vulnerable by its record-high masts. So much so that the boat next door, with two smaller masts, did not sink." Codacons returns to the story of the shipwreck of the Bayesian to denounce the risks that, in the name of luxury, are assumed when building large ships. According to the consumer association, this is the case of the boat that sank in recent days, "characterized by excesses and solutions to the limit that could - the conditional is a must - have cost the lives of passengers. This is a consideration that, beyond human error, is shared by some of the leading Italian experts on the subject," reads a note. One of whom prepared a technical report for Codacons, which reads, among other things: "The boat was not suitable for navigation except with special attention and precautions that go beyond those usually required. And the designer and owner should have indicated them." Codacons increases the dose: "What was missing was a careful risk analysis". The Association, which in recent days has filed a complaint to shed light on the matter, does not rule out the error on the part of the crew but points out how boats of this type take the proven sailing ideas to extremes. "Such extreme boats can have difficulties in the event of problems," says Carlo Rienzi. "But it will be the investigations that will clarify the causes of the tragedy," he concludes.

 

Bayesian yacht sinking: Families and crew deserve truth, not baseless accusations (nautilusint.org)

 

But they aren't going to be getting the truth. None of us are. All of the investigative effort by all parties is going to be directed towards building a defense against lawsuits. The product of the investigations will not be what caused the accident, it will be a list of alternative scenarios that are difficult and expensive for the opposition to disprove. There isn't anything like an NTSB investigation of a commercial aircraft accident. Lawsuits can only be about what really did happen. Showing that a problem would have come back to bite you sooner or later isn't on point, and you aren't going to reach the level of gross negligence against Perini Navi. Lynch was a risk taker. But here, he wasn't just playing with other peoples money, he was risking lives.

Also, I doubt much of anything new can be learned from the yacht itself that wouldn't be challenged in court since anything could have been tampered with by now. I suppose there are a few things that could be ruled out. Crew depositions are probably the best we can hope for.

A few numbers are being bandied about, supposedly from former crew including a former captain. Angle of vanishing stability was 77 degrees. Down flooding angle was reported as 45 degrees per the stability booklet. The boat had 30 tons more ballast than its sisterships and sat 4 inches lower in the water. The centerboard was supposed to be lowered while sailing; and any time it was 60 miles offshore. The thinking seems to be that all of the compartments were susceptible to flooding through the ventilation systems at around 45 degrees of heel. However that would have allowed people to escape the suites. I suspect 45 degrees is well past the angle of maximum righting moment, so if the wind got her that far, she would keep going.

I think she went over very quickly until her mast stuck in the mud. If she had upset her anchor in a wind shift and pulled it under the hull, it would have done a fine job of rolling the vessel and could have turned her broadside to the wind. It looks like a wind that can put her over 35 degrees would be about enough to send her over the rest of the way. I spit-balled some numbers for wind on the beam and didn't like the answers.

 

56m luxury sailing yacht sinks off Sicily, 7 missing | Page 133 | Sailing Anarchy Forums

 

@Tad has done an excellent job of assessing the stability of Bayesian on his Facebook page, simply by using the information that is freely available online, and then applying his 30+ years of knowledge and design experience of large sailing vessels. .
Here is a link to his page.
Tad Roberts https://www.facebook.com/profile.php?id=100009398593049

 

FWIW, I see a different issue here.
All the working crew were saved, most of the passengers (and the chef, an 'idler') were not. Occum's Razor says that the crew were up and about, the passengers were not. This would be typical in an "all hands on deck; batten down the hatches" reaction to an intense storm event.
You can debate all you want about the stability and downflooding, but in this incident like that of the SEWOL, perhaps everyone should have been awake and on deck.

 

This is the Stability curve from Tad's Facebook page. He also got about 35 degrees as the point of Maximum Righting Moment.



The displacement used to generate the curve wasn't listed. What is needed now is a set of overlays of what the heeling moment is for a range of wind speeds from about 50 knots to 100 knots on the beam. It varies considerably with heel angle once you get passed 30 degrees or so, but we don't need data for much more than 45 degrees. Consider three cases - anchor resisting load under normal conditions, vessel adrift, and anchor chain wrapped under hull.

A second matter is the roll momentum of the ship. Video of a similarly sized yacht getting rolled on beam ends shows just how fast they can get tossed. Roll rates of 1 rad/sec seem possible even for boats of this size. I'd like to compare the kinetic energy of the yacht rolling at 1 rad/sec with the area under the righting moment curve, which is a potential energy term. But the inertia about the roll axis isn't a commonly published term. It's fine if you add ballast and the area under the RM curve rises in proportion to axial inertia term. But if it doesn't - if you add a taller mast and ballast - and the area under the curve doesn't rise in proportion to axial moment, you haven't gained all you thought you gained. It seems like a gust that would heel Bayesian to 30 degrees could get her over the hump with roll momentum. So there is very little reduction of aerodynamic drag from heeling. It's much like getting blown over on a catamaran or motor yacht.

 

Displacement 1,132,200 lbs and GM = 7.63'. Limit of positive stability is 73 degrees. This is a centreboard up, half-load condition.

 

HMS Captain

HMS Captain (1869) - Wikipedia https://en.m.wikipedia.org/wiki/HMS_Captain_(1869)

1.2 Million Newtons-meters at 14 degrees Heel

---

Bayesian held out at just under 5 million Newtons-meters at 30 degrees Heel

And a 50-meter-per-second wind produced perhaps 10 million Newtons-meters.

It would be necessary to calculate the drag of each element (including the hull and antennas) and its lever arm; but by rough estimation, from a photograph there is perhaps maybe something like 160 (!?) square meters (furled sails, mast and cables) and let's suppose, simplifying, a drag coefficient of 1

Dynamic pressure = 1 (Cd) x 50 x 50 (Wind speed squared) x 0.5 x 1.2 kg (Air density)

Dynamic pressure x 160 = 240,000 Newtons

Let's assume a lever arm of 40 meters between the force of the wind and the lateral force of the water

240,000 x 40 = 9,600,000 Newtons-meters

But

(A) liter of air weighs 1.2 grams; but a liter of water weighs 1 kg, and a "downburst" is wind ... and water

Downburst - Wikipedia https://en.m.wikipedia.org/wiki/Downburst




(B) and on the other hand, it must be taken into account that this is a static calculation and the momentum must be taken into account.

 

prof. Tetsuya Fujita



On professor Fujita's scale it was perhaps 'only' F1-F2 (?)

 

If the megayacht can withstand 4.5 million Newtons metres in a static calculation, we can only count on about perhaps only 3 million in a dynamic calculation

so capsizing even if we assume a wind speed of 40 metres per second, fewer square metres and somewhat less lever arm (but we would have to add the hull and not forget the water that was blowing in)

 

I forgot the boom

We can play with adjusting the numbers and make a more precise estimate, but the conclusion is the same.

For the hull we can choose a drag coefficient of 0.8, for the cables 1.1 ... each element with its coefficient and its lever arm and add it all up

and wind speed according to height

Well, we can refine the question, but it won't change substantially

What I don't know is how to add the water, which we must not forget is about 800 times denser than air

The torrential water was flying

 

I understand the details of the static calculation, for example, you would have to take into account the hull of the yacht that is heeled over, which increases the wind shield, and the height of the centre of pressure.

The dynamic question is what I don't know how to address.

And what really intrigues me is whether there is any way to take into account the force of a torrential rain.