Bayesian Interim Report

[franksingleton]

From the MAIB interim report -
Early Italian weather forecasts ahead of the accident predicted intense and persistent rain, mainly in theform of showers or thunderstorms…[with] storms [being] accompanied by strong wind gusts3. At 2100 UTCon 18 August, Italian forecasters issued a gale warning of northwesterly gale force 8 winds for Sardinia and Corsica with associated isolated thunderstorms with local gusts for Sicily. This was updated and reiteratedat 0000 UTC on 19 August 2024.

These sound like typical conditions for a super cell. But, as far as I know, there is no way in which a specific warning could have been given. I doubt that any forecaster would even put the risk of a super cell into a forecast. For much of the ares that would be covered, it would be a gross over forecast. Attempts to warn of a super cell a few hours ahead would be counter productive. These individual storms develop and die very quickly. Even when first seen on radar would be too late for a warning to be given.


The questions really boil down to the yacht design and seamanship. We will have to await the final MQIB report and, perhaps, any court case either by the Italians or civil litigation.

 

[billskip]

The MAIB report that started this thread is a good place to look for an analysis of the weather on the night in question. I would suggest it supports lustyd's observations. The indications are that the wind speed and direction were such that the boat heeled to an angle greater than its calculated AVS for its configuration (board up).

One of the unanswered questions is if the crew had known about the reduced stability could they have taken action to avoid the wind that knocked the boat down - or minimised the the water ingress that sank the boat? The builder claims they could, but the MAIB interim report suggests not

What on earth has all that got to do with lustyds statement ?

 

[Tranona]

What on earth has all that got to do with lustyds statement ?

See post #381. while the conditions on the night could lead to the development of "super cells" they are impossible to predict accurately. The boat anchored close by did not seem to have been affected in the same way - it will be interesting to hear more about their experience.

As I understand it the point that lustyd was making is that while the conditions for extreme weather can be identified, the specific phenomenon that it is believed to have occurred is not predictable in such a way that warnings might be given.

 

[billskip]

See post #381. while the conditions on the night could lead to the development of "super cells" they are impossible to predict accurately. The boat anchored close by did not seem to have been affected in the same way - it will be interesting to hear more about their experience.

As I understand it the point that lustyd was making is that while the conditions for extreme weather can be identified, the specific phenomenon that it is believed to have occurred is not predictable in such a way that warnings might be given.

Again what has all that got to do with me and my post # 377 ?
Do you not understand my post #377? it's only one word!!

 

[Tranona]

Again what has all that got to do with me and my post # 377 ?
Do you not understand my post #377? it's only one word!!

You asked for a link - that is a source for the statement. In fact it was not a specific quote that was made so I suggested a source to support.

Of course I could have misunderstood as just posting one word leaves it open to interpretation - "Link" could have referred to part of the chain that connected the anchor to the boat for example. If you want more accurate information perhaps best to ask precisely what you want rather than a cryptic single word.

 

[franksingleton]

Bill, your eloquent one word was in response to

It wasn’t an average night, how can’t you understand that? It wasn’t predicted in any way whatsoever, that’s a matter of public record.
As you rightly say, there was a professional skipper who recorded all actions and observations so none of this is under contention.

Your aversion to the facts is likely to get the thread shut down for pointless speculation like the last one.

My emboldening.
I suggest that lustyd is wrong here as my #381 makes clear. I am sure that the forecaster who wrote the text quoted by MAIB would claim that his warning of thunderstorms with strong gusts was good guidance. I note that lustyd “likes” #363. The supercell was not forecast and I see no prospect of us being able to predict individual ones. The conditions for supercells were well predicted.

 

[westernman]

Bill, your eloquent one word was in response to


My emboldening.
I suggest that lustyd is wrong here as my #381 makes clear. I am sure that the forecaster who wrote the text quoted by MAIB would claim that his warning of thunderstorms with strong gusts was good guidance. I note that lustyd “likes” #363. The supercell was not forecast and I see no prospect of us being able to predict individual ones. The conditions for supercells were well predicted.

I will also add that F8 for a well found large yacht is nothing special and does not pose any difficulties

 

[lustyd]

Bill, your eloquent one word was in response to


My emboldening.
I suggest that lustyd is wrong here as my #381 makes clear. I am sure that the forecaster who wrote the text quoted by MAIB would claim that his warning of thunderstorms with strong gusts was good guidance. I note that lustyd “likes” #363. The supercell was not forecast and I see no prospect of us being able to predict individual ones. The conditions for supercells were well predicted.

The yacht would cope just fine at anchor in a F8 with gusts, and I’m sure has in the past on many occasions.
Your own post said that forecasters would not include those (and in this case didn’t, so it’s moot), and our ability to predict the few hundred metres affected is essentially zero, which is what really matters to the skipper.
Would any of us cancel a charter based on the information provided? I’d suggest that’s a very strong no.

 

[lustyd]

Again what has all that got to do with me and my post # 377 ?
Do you not understand my post #377? it's only one word!!

Perhaps let’s put it another way, can you provide a link to a prediction for the conditions in that location for that date showing that a waterspout would hit?
As I said, the reports and other sources all agree it wasn’t predicted and our resident expert said forecasters don’t include that information regardless.

 

[Bouba]

Perhaps let’s put it another way, can you provide a link to a prediction for the conditions in that location for that date showing that a waterspout would hit?
As I said, the reports and other sources all agree it wasn’t predicted and our resident expert said forecasters don’t include that information regardless.

And what can you do even if all hands are on deck and somebody spots a waterspout while at anchor ?
It’s really now a case of hoping that the designers, builders and regulators have done their jobs

 

[lustyd]

And what can you do even if all hands are on deck and somebody spots a waterspout while at anchor ?
It’s really now a case of hoping that the designers, builders and regulators have done their jobs

Exactly. Sometimes it just comes down to bad luck.

The designers, builders and regulators all did their job here and the boat performed within specification. It's not a popular view on these forums but not every boat is an expedition yacht built for the Arctic, and neither are all accidents reasonably avoidable

 

[Bouba]

Exactly. Sometimes it just comes down to bad luck.

The designers, builders and regulators all did their job here and the boat performed within specification. It's not a popular view on these forums but not every boat is an expedition yacht built for the Arctic, and neither are all accidents reasonably avoidable

I would normally agree on those points....but was the mast height the result of good design...or....an arms race with the attitude of we can build it so we shall ?.....and the retractable keel....with such a huge weight to ballast it, why was it necessary to have it retractable....surely raising the CoG can’t be good ?

 

[billskip]

I would normally agree on those points....but was the mast height the result of good design...or....an arms race with the attitude of we can build it so we shall ?.....and the retractable keel....with such a huge weight to ballast it, why was it necessary to have it retractable....surely raising the CoG can’t be good ?

When goal posts are moved to justify what is said, ...anything goes...

 

[Mark-1]

And what can you do even if all hands are on deck and somebody spots a waterspout while at anchor ?
It’s really now a case of hoping that the designers, builders and regulators have done their jobs

Moreover I think I'd rather be in an anchored yacht than onshore if such an event was forecast. A yacht is designed to be violently put on its side in (pretty much) normal use and it's under bare poles. The roof of a house falling in would be a far greater fear.

 

[Mark-1]

I would normally agree on those points....but was the mast height the result of good design...or....an arms race with the attitude of we can build it so we shall ?.....and the retractable keel....with such a huge weight to ballast it, why was it necessary to have it retractable....surely raising the CoG can’t be good ?

Well yeah, but we can't blame the designers, they designed what they were asked for. The fundamental problem is the requirements that these craft are built to inherently lead to vessels with all these flaws.

Also, in general, I'm not sure we know for a fact this vessel was hit by a downdraft. It's certainly possible but we don't know and I doubt we ever will. It's entirely possible it was tipped over past 45 degrees by a "normal" but incredibly strong squall and quickly turned over as its COG changed as it flooded at 15% of its weight per minute. (I haven't checked the MAIB report to see how fast it turned over, whether it was 10 seconds or 2 minutes, so could be wrong on that last point.)

 

[billskip]

Well yeah, but we can't blame the designers, they designed what they were asked for. The fundamental problem is the requirements that these craft are built to inherently lead to vessels with all these flaws.

Also, in general, I'm not sure we know for a fact this vessel was hit by a downdraft. It's certainly possible but we don't know and I doubt we ever will. It's entirely possible it was tipped over past 45 degrees by a "normal" but incredibly strong squall and quickly turned over as its COG changed as it flooded at 15% of its weight per minute. (I haven't checked the MAIB report to see how fast it turned over, whether it was 10 seconds or 2 minutes, so could be wrong on that last point.)

I could be mistaken...but...I'm sure I've seen (video ) the sister ship being knocked over in a severe storm and righting itself, I believe it was in port somewhere, so would possibly have keel up...but my point is it righted itself...how far over it went of course is difficult to tell but looked to be extreme...so if the identical hull (if identical) can possibly sustain a knock down, but not necessarily a prolonged duration being held down by, as you say, downdraft...I can't seem to find any detail the incident now.

 

[lustyd]

I'm not sure we know for a fact this vessel was hit by a downdraft. It's certainly possible but we don't know and I doubt we ever will.

There’s a video of it so I think it’s pretty well accepted.

 

[lustyd]

I would normally agree on those points....but was the mast height the result of good design...or....an arms race with the attitude of we can build it so we shall ?.....and the retractable keel....with such a huge weight to ballast it, why was it necessary to have it retractable....surely raising the CoG can’t be good ?

Does it matter? The mast didn’t affect the boat in normal expected conditions for 17 years. It was only rare, unexpected weather that led to a problem and while some people design for literally every eventuality, most don’t.
The UK has hundreds of thousands of flat roofs despite them failing in relatively benign conditions. Caravans rarely survive storms. Design parameters are a fact of life and I doubt anyone involved would change much on this design even in hindsight.
The keel was for sailing and although the numbers are bigger it’s an extremely common configuration.

 

[Mark-1]

There’s a video of it so I think it’s pretty well accepted.

The MAIB report doesn't say it was a downdraft, merely that the conditions were right for it, and I am skeptical you can video wind at sea at night.

 

[franksingleton]

The yacht would cope just fine at anchor in a F8 with gusts, and I’m sure has in the past on many occasions.
Your own post said that forecasters would not include those (and in this case didn’t, so it’s moot), and our ability to predict the few hundred metres affected is essentially zero, which is what really matters to the skipper.
Would any of us cancel a charter based on the information provided? I’d suggest that’s a very strong no.

I will also add that F8 for a well found large yacht is nothing special and does not pose any difficulties

You omit the reference to thunderstorms and strong gusts. In August, storms in that area can be vicious. The problem, meteorologically is that it is too easy to over-warn of such storms. There must be many occasions when the forecaster might like to mention the risk of supercells but sailors would become blase about them. All they can do is warn of thunderstorms on the assumption that any sensible, experienced sailor will think about squalls and consider what would happen to them.