Bayesian Interim Report

[Bouba]

Many (most?) superyachts pay for their keep by being chartered out.....schedules have to be kept because time is valuable to wealthy people....if the craft requires a captain with a commercial ticket...then it’s commercial, surely ?

 

[Mark-1]

Many (most?) superyachts pay for their keep by being chartered out.....schedules have to be kept because time is valuable to wealthy people....if the craft requires a captain with a commercial ticket...then it’s commercial, surely ?

I have a feeling there might be some legal cases around exactly that issue! - But the MAIB say it was a private vessel being privately operated and they do it on line one of the narrative. I can't imagine that's an accident or a mistake, in fact it seems quite pointed to me.

It certainly took me by surprise - so much so that it stuck in my mind which is why I was able to quote it. I'm sure I'm not the only one who raised their eyelids!

 

[lustyd]

From the first line of the MAIB Narrative: "privately owned and operated yacht".

And yet fully crewed and likely chartered between trips.

 

[Chiara’s slave]

I've no idea, my point was that it was not inhibited from sailing passages by its LWL and for that comparison we only need to know what it does on 'normal' passage under engine.

1) Link to it so we can see exactly what he said.

2) 12.5 kts is the only relevant number for comparison since that is the speed it would be doing on passage if it wasn't sailing. So no matter how crap it is downwind it only has to beat 12.5kts to be better off sailing in terms of speed. I assume there will be times it can do that and I am sure there will be times it can't. (For whatever reason.)

3) Yes. Apparent wind is a thing. I don't think you need to explain it to a sailing forum!

Well exactly. Economic cruising under engine is governed by all sorts of factors independent of hull speed. Whereas for a full displacement boat, ie non planing, hull speed is the ‘target’ when sailing. Achieving 90% of it is fairly usual. The times when it can’t would be light, and maybe heavy, winds or unfortunate sea conditions, you’d think.

 

[lustyd]

It doesn't cruise at its hull speed. It cruises (under engine) at 12.5 kts.

Which is irrelevant to the discussion we were having.

 

[Mark-1]

And yet fully crewed and likely chartered between trips.

From memory I'm pretty sure it wasn't charter-able at that point but had been in the past. (Or maybe sister ships had.)

But agree re crew.

Either way, I'm not the MAIB, I just quoted their words.

 

[Mark-1]

Which is irrelevant to the discussion we were having.

I've explained why it's the only relevant number in post 219, and others. I'll duck out of the LWL debate now and leave the last word to you.

EDIT: I wonder if someone with better google fu than me can find polars for her or her sisterships, or perhaps something similar.

 

[lustyd]

post 219

Sorry yes I missed that and you’re kind of right on that count. A flapping sail of that size though would be an expensive proposition, potentially more so than the fuel if it wears quickly due to flogging. I can’t even imagine the cost of a suit of sails for these beasts!

Yes I’d love to see the polars but imagine none of them really sail enough for it to matter. Parsifal 3 does enter regattas though so perhaps the owners are more sail oriented than many assume

 

[ylop]

Whilst you guys bicker about stuff that really will make no difference to survivors/families, and likely do nothing to prevent future disaster the MAIB report was only an interim one, and I note the full investigation is considering aspects beyond those in this report including escape routes and emergency procedures. Better stability information MIGHT help avoid a repeat, but the conclusion seems to be that in freaky enough winds any boat may get knocked down and if those winds are unexpected might have big issues. The obvious questions to my mind are, should a dragging anchor have resulted in a general alarm, did the passengers know what to do once it was in trouble, and presumably the reason they went down with the boat was they were trapped in their cabins - from knockdown to sinking she was afloat on her side for at least 18 minutes on the timeline narrated by the MAIB.

 

[Mark-1]

in freaky enough winds any boat may get knocked down

...but sailing boats typically survive knockdowns. and 70knots (as stated in the MAIB report) isn't unheard of even in the UK. Many of our own boats will already have survived 70knot gust on their moorings. (Probably all of them if they're old enough.) There's a harbour in Porticello which experienced the same squall where no vessels were lost (ICBW), a nearby anchored vessel wasn't sunk.

Yes, I'm sure there are conditions that no vessel can survive, but there doesn't seem much evidence that this was such conditions. The MAIB pre-report isn't talking about 150mph vertical microbursts.

Meanwhile we know this vessel significantly downfloods a little over 40 degrees. That's pretty unusual for a sailing boat.

Personally (based on zero knowledge of ship design), I think it's entirely possible that the compromises that this style of vessel require make them more likely to come to harm than other vessels when sailing and maybe motoring/anchored/berthed as well.

I'm sure there are a million other things to consider as well.

EDIT: Deleted the bits that were wrong!

 

[SaltIre]

I'm sure there are a million other things to consider as well.

MAIB team have a lot of work to do, if you are correct.

 

[boomerangben]

...but sailing boats typically survive knockdowns and 70knots (as stated in the MAIB report) isn't unheard of even in the UK. Many of our own boats will already have survived 70knot gust on their moorings. (Probably all of them if they're old enough.) There's a harbour in Porticello which experienced the same squall where no vessels were lost (ICBW), a nearby anchored vessel wasn't sunk.

Yes, I'm sure there are conditions that no vessel can survive, but there doesn't seem much evidence that this was such conditions. The MAIB pre-report isn't talking about 150mph vertical microbursts.

Meanwhile we know this vessel significantly downfloods a little over 40 degrees. That's pretty unusual for a sailing boat.

Personally (based on zero knowledge of ship design), I think it's entirely possible that the compromises that this style of vessel require make them more likely to come to harm than other vessels when sailing and maybe motoring/anchored/berthed as well.

I'm sure there are a million other things to consider as well.

From the report, Met Office concluded at the bottom of page 5, top of page six, there was evidence of a significant supercell within the mesocyclonic front, possible winds in excess of 100mph and possible tornadic winds.

 

[Mark-1]

From the report, Met Office concluded at the bottom of page 5, top of page six, there was evidence of a significant supercell within the mesocyclonic front, possible winds in excess of 100mph and possible tornadic winds.

Thanks for the correction, here's the text if anyone else is interested:

The Met Office study of satellite imagery indicated that the mesocyclonic storm front was demonstrating
the properties of a significant supercell with associated downdrafts and possible near-surface winds in
excess of 100 miles per hour (87kts). The study concluded that a mesocyclonic storm was highly likely with an associated supercell being probable. It also concluded that tornadic waterspouts and downdrafts were
possible where local winds could reach extreme hurricane force well in excess of 64kts. Such tornadic
waterspout features could be of very limited horizontal extent (50m to 100m wide)

 

[zoidberg]

May I 'toss hat into ring'...? Add a tuppence worth?

"Yes, the force of the wind increases EXPONENTIALLY with the square of its speed. This means that if the wind speed doubles, the force exerted on an object increases fourfold. For example, a 40 mph wind is not twice as strong as a 20 mph wind; it's four times stronger."

I'm confident some have hoisted this in. I similarly suspect that some others haven't yet managed to imagine a 'wind-over-deck' with horizontal spray at over 87 knots. Can one even SEE in that, never mind work on a 90 degree heeled deck?

One could manoeuvre, take-off and land a Canberra bomber - even a lightly-fueled Vulcan - at that speed.

I'm now concerned about what we can learn from this that has practical relevance to some of us..... which is the declared aim of the MAIB Safety Digests.
To that end, I'll raise sew a fresh thread so as not to deflect this important one.

 

[dunedin]

Many (most?) superyachts pay for their keep by being chartered out.....schedules have to be kept because time is valuable to wealthy people....if the craft requires a captain with a commercial ticket...then it’s commercial, surely ?

Over 24m is into different regulations, skipper certification and manning rules - even if a "private" vessel.
Some on the mobo forum are experts in this, and why 23.99m is a very popular size for big private vessels

 

[Tranona]

Whilst you guys bicker about stuff that really will make no difference to survivors/families, and likely do nothing to prevent future disaster the MAIB report was only an interim one, and I note the full investigation is considering aspects beyond those in this report including escape routes and emergency procedures. Better stability information MIGHT help avoid a repeat, but the conclusion seems to be that in freaky enough winds any boat may get knocked down and if those winds are unexpected might have big issues. The obvious questions to my mind are, should a dragging anchor have resulted in a general alarm, did the passengers know what to do once it was in trouble, and presumably the reason they went down with the boat was they were trapped in their cabins - from knockdown to sinking she was afloat on her side for at least 18 minutes on the timeline narrated by the MAIB.

I suspect that publishing this interim report is putting down a marker to say that the stability figures were much lower than those implied by the builder, whose boss has been very vocal in his claim that the boat was "unsinkable". He also claimed that the fault was firmly with the crew, whereas the MAIB is saying there is no evidence that the crew did not act inappropriately. If I recall rightly when the rig of the design was changed from a ketch to the lofty sloop 40 tonnes of extra ballast were added. The Wolfson work on the effect of wind on the boat, particularly the mast is new and probably was never considered at the design stage, or at least recognised but not fully considered because of lack of firm data.

 

[boomerangben]

May I 'toss hat into ring'...? Add a tuppence worth?

"Yes, the force of the wind increases EXPONENTIALLY with the square of its speed. This means that if the wind speed doubles, the force exerted on an object increases fourfold. For example, a 40 mph wind is not twice as strong as a 20 mph wind; it's four times stronger."

I'm confident some have hoisted this in. I similarly suspect that some others haven't yet managed to imagine a 'wind-over-deck' with horizontal spray at over 87 knots. Can one even SEE in that, never mind work on a 90 degree heeled deck?

One could manoeuvre, take-off and land a Canberra bomber - even a lightly-fueled Vulcan - at that speed.

I'm now concerned about what we can learn from this that has practical relevance to some of us..... which is the declared aim of the MAIB Safety Digests.
To that end, I'll raise sew a fresh thread so as not to deflect this important one.

Keep an eye on the weather forecast and run away (either by boat itself if fast enough or get safely on land if tender is fast enough) if such an intense squall line builds. Or trust in God.

The importance of keeping proper watch, I suppose, making use of radar to watch for weather, but if you are in the lee of land, the radar is of limited use

 

[Mark-1]

I suspect that publishing this interim report is putting down a marker to say that the stability figures were much lower than those implied by the builder,

Of course, there are no stability figures for keel up configuration. Then there are grand pianos and loose marble busts falling down to the leeward side to consider.

 

[ylop]

Of course, there are no stability figures for keel up configuration. Then there are grand pianos and lose marble busts falling down to the leeward side to consider.

that's why I don't have such things on board ;-)

 

[Tranona]

Of course, there are no stability figures for keel up configuration. Then there are grand pianos and lose marble busts falling down to the leeward side to consider.

It is not just the keel up stability figures that were missing but the keel down according to Wolfson may well be lower than the builder thought. Keel up stability curves are not unusual - pretty sure it is a requirement of the RCD. southerly for example published them for their boat over 20 years ago.