Bayesian Interim Report

[ylop]

Whilst the hight of the mast was in part responsible for the low ( relatively speaking) righting moment it was the very low downflooding angle which was more a consequence of accommodation design that seems more problematic.

Oddly then the MAIB report doesn’t highlight the downflooding angle - but did highlight the AVS issue! The two are obviously interlinked - boat the flips but doesn’t flood is embarrassing, uncomfortable and potentially painful but not automatically life threatening whilst a boat that floods early but is so stable that it is almost impossible to reach that angle is probably OK. It strikes me that the fundamental job of the designer is to get that balance right, make sure the builder and operator understand what that means to actual use.

I very much doubt that the owner ever expected that the yacht would heel to any significant degree hence its use largely under engine and not being sailed in any winds much above 12knts as has been reported.

Yeah so it was the designers job to know when that might happen eg, by running simulations like the MAIB did so they could mitigate the risks.

All in all a very unsatisfactory design as a sailing yacht but one perfectly capable of performing within a narrow set of parameters which were obviously exceeded on the night it sank.

And those were parameters which I suspect the owner would have said they wanted it to cope with.

 

[bedouin]

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.

I don't think there is a sister ship per se - I think the other boats with the same hull are ketch rigged. Bayesian had more ballast (30 tonnes more) to compensate and so was said to sit a few inches lower in the water. And most of the others did not have the swing keel (IIRC)

 

[E39mad]

The video that has been used since this disaster to show a yacht being knocked flat under bare poles was in New Zealand. It was not a sister ship to Bayesian but approx 100 foot monohull knocked to 90 degrees on its berth in a marina at night. A catamaran was flipped in the same micro burst.

 

[RunAgroundHard]

 

[DreadShips]

Oddly then the MAIB report doesn’t highlight the downflooding angle - but did highlight the AVS issue!

Remember that what the MAIB doesn't say might be relevant to the Italian criminal investigation...

 

[ylop]

Remember that what the MAIB doesn't say might be relevant to the Italian criminal investigation...

I’m not sure I follow. The MAIB generally don’t care about what they do/don’t say being relevant to criminal or civil proceedings. They don’t seem to edit their reports to omit detail to protect the accused or ensure prosecutors have an easy task. They might face issues with people exercising their right to silence but the Downflooding Angle is a matter of physics not memory so seems no reason that they don’t know it (or potential the various possibly values depending on the state of hatches). It is only an interim report - I’m sure it will be mentioned in the full report, but they chose to publish an interim report (which is not that common for them) presumably because they thought the “world” should know about their AVS findings sooner than a final report.

 

[WindyWindyWindy]

First point. Indulge my dit please?
I was once ...a long long time ago...a UK DTp (Dept of Transport) Engineer and Ship Surveyor...the "good old days" before yacht codes and the MCA were even a thing.
I walked off several large superyachts, then under survey as Ships under UK Merchant Shipping legislation. This was because some crews/owners /managers refused to comply as they saw themselves as "special". They refused to comply with standards set for the little people.

Interesting, but presumably if the surveyor walks off then the certificate doesn't get issued and probably the insurance isn't valid. The skipper would refuse to sail it putting their own licence at risk if they did so. Finally charter licences wouldn't be issued as the paperwork wouldn't be complete.

I've been asked for all sorts of weird stickers on things by one surveyor and the next saying it doesn't matter. There's never been an option not to comply though.

 

[RunAgroundHard]

Interesting, but presumably if the surveyor walks off then the certificate doesn't get issued and probably the insurance isn't valid. The skipper would refuse to sail it putting their own licence at risk if they did so. Finally charter licences wouldn't be issued as the paperwork wouldn't be complete.

I've been asked for all sorts of weird stickers on things by one surveyor and the next saying it doesn't matter. There's never been an option not to comply though.

For an item like that, a sticker on a crane, it would not be material to refusing to class, re-class the vessel to the CA standard. Instead, it would be on a list of items to be addressed within a time frame, all of which can be challenged by the vessel owner, manager. It might not even end up on a list, but be noted as a recommendation, not mandatory.

 

[boomerangben]

I don’t get this fascination with downflooding. The vessel was approved with whatever downflooding angle it had. It was knocked down beyond its (legal) AVS in less than 15 seconds. It was going to downflood as a result of that knock down, just like any other large vessel would. I am pretty certain the passenger ferry I get every two weeks has a downflooding angle of far less than 90 degrees and possible less than 40 deg

Surveyors, Inspectors and Naval Architects are bound by rules and regulations, not opinions. If the rules said it could be built and operated that way, then the owner and crew could safely operate that vessel. The rules and regulations don’t guarantee safety in the same way, your safety is not guaranteed in your own boat, a passenger vessel or any other vessel or indeed any mode of transport or leisure activity bound by regulations born out of safety concerns.

Perhaps the Bayesian was a bit extreme, perhaps the regulations might be altered as a result, but this wasn’t an unsafe vessel. Like any vessel, it wasn’t without hazards. Like other vessels it experienced a weather event that might have contained an unsurvivable (in terms of the vessel) phenomenon. It is not the first vessel to succumb to weather, it won’t be the last. To design out weather, you need a submarine. And the view from a submarine is, I gather pretty limited and the sun beds invariably damp

 

[Mark-1]

I am pretty certain the passenger ferry I get every two weeks has a downflooding angle of far less than 90 degrees and possible less than 40 deg

I'd be amazed if normal commercial ships of any kind have a downflooding angle below 40° or even anywhere near 40°. They typically have massive freeboard and infinate scope to route vents upwards miles away from the water right at the top on the centre line the way funnels are situated. I'm sure they have their own flaws but downflooding isn't one of them.

If you're talking about a ferry used exclusively in sheltered waters then maybe, but I'm sure they have operational limits on weather. They aren't crossing oceans in normal use the way this vessel did.

In fact maybe the reason the regs don't seem to have considered the downflooding angle in this vessel is that downflooding simply isn't a concern on a normal ship, it would turn over long before it flooded. The low freeboard of quasi-sailing vessels like Bayesian combined with a keel (no matter how light) meant the opposite to the normal problem, AVS was less important and down flooding was more important. Ironic given her ending.

 

[dunedin]

I don’t get this fascination with downflooding. The vessel was approved with whatever downflooding angle it had. It was knocked down beyond its (legal) AVS in less than 15 seconds. It was going to downflood as a result of that knock down, just like any other large vessel would. I am pretty certain the passenger ferry I get every two weeks has a downflooding angle of far less than 90 degrees and possible less than 40 deg

……

I guess there is perhaps a bit of the “chicken and the egg” here. Did it heel over beyond its AVS before it started flooding, or did the down flooding reduce stability such that it then heeled over beyond its AVS?
Either way an early downflooding angle IS important, as once get water inside then whatever was it’s original dry ship stability curve suddenly becomes irrelevant.

 

[flaming]

I guess there is perhaps a bit of the “chicken and the egg” here. Did it heel over beyond its AVS before it started flooding, or did the down flooding reduce stability such that it then heeled over beyond its AVS?
Either way an early downflooding angle IS important, as once get water inside whatever was it’s original dry ship stability curve is suddenly becomes irrelevant.

I definitely read the report as saying it went over beyond its AVS well before significant downflooding would have occurred.

 

[Mark-1]

I definitely read the report as saying it went over beyond its AVS well before significant downflooding would have occurred.

I think that is most likely but I'm not sure the report said that, and people were escaping from below and I don't recall it being stated that they were escaping from a nearly turtled vessel.

I didn't close read the report, though maybe I missed the critical bit.

So AFAICT the jury is still out. (Although we can agree a quick inversion is most likely.)

....but even if it turns out downflooding angle is irrelevant in this incident, a low downflooding angle is still really bad news in a vessel that has any pretentions to sail at all. ....and frankly in any vessel. It's certainly worth a mention when discussing these vessels.

 

[flaming]

....but even if it turns out downflooding angle is irrelevant in this incident, a low downflooding angle is still really bad news in a vessel that has any pretentions to sail at all. ....and frankly in any vessel. It's certainly worth a mention when discussing these vessels.

Oh for sure,

 

[boomerangben]

I guess there is perhaps a bit of the “chicken and the egg” here. Did it heel over beyond its AVS before it started flooding, or did the down flooding reduce stability such that it then heeled over beyond its AVS?
Either way an early downflooding angle IS important, as once get water inside then whatever was it’s original dry ship stability curve suddenly becomes irrelevant.

Given the fact the vessel reached its AVS in less than 15 seconds and the minimum angle of downflooding required by the LY3 code of the MCA is 40 degrees, I would suggest that whilst downflooding will probably have occurred at some point in the “less than 15s” it’s contribution to stability would be small compared with the over turning moment caused by the wind

 

[boomerangben]

I'd be amazed if normal commercial ships of any kind have a downflooding angle below 40° or even anywhere near 40°. They typically have massive freeboard and infinate scope to route vents upwards miles away from the water right at the top on the centre line the way funnels are situated. I'm sure they have their own flaws but downflooding isn't one of them.

If you're talking about a ferry used exclusively in sheltered waters then maybe, but I'm sure they have operational limits on weather. They aren't crossing oceans in normal use the way this vessel did.

In fact maybe the reason the regs don't seem to have considered the downflooding angle in this vessel is that downflooding simply isn't a concern on a normal ship, it would turn over long before it flooded. The low freeboard of quasi-sailing vessels like Bayesian combined with a keel (no matter how light) meant the opposite to the normal problem, AVS was less important and down flooding was more important. Ironic given her ending.

I don’t know what a typical angle of downflooding of a ship is. I did once calculate the AoDF for an offshore drilling rig to be 18 degrees but memory fade might have made a fool of me. Regulations cite minimum criteria for the GZ curve parameters relating to 40 degrees and different criteria for when the angle of downflooding is less than 40 degrees. So I suspect but may be wrong that 40 degrees is a reasonable AoDF and might in some cases be less.

The MCA require a minimum ApfDF of 40 degrees. That includes any opening that would lead to progressive flooding. As far as the regs re concerned (notwithstanding ABS might have other criteria) Bayesian’s AoDF was reasonable and met requirements.

 

[dunedin]

I don’t know what a typical angle of downflooding of a ship is. I did once calculate the AoDF for an offshore drilling rig to be 18 degrees but memory fade might have made a fool of me. Regulations cite minimum criteria for the GZ curve parameters relating to 40 degrees and different criteria for when the angle of downflooding is less than 40 degrees. So I suspect but may be wrong that 40 degrees is a reasonable AoDF and might in some cases be less.

The MCA require a minimum ApfDF of 40 degrees. That includes any opening that would lead to progressive flooding. As far as the regs re concerned (notwithstanding ABS might have other criteria) Bayesian’s AoDF was reasonable and met requirements.

One would expect differnt design requirements for a sailing vessel designed to heel, compared to a conventional ship designed to be level, in normal working conditions.

 

[boomerangben]

One would expect differnt design requirements for a sailing vessel designed to heel, compared to a conventional ship designed to be level, in normal working conditions.

The MCA do. They require a minimum for sailing vessels of 40 degrees. For motor vessels it can be less than 40 degrees providing the GZ curve maintains a suitable reserve of stability.

I suppose we expect small sailing boats to heel to 40 degrees and beyond before down flooding. A broach can easily result in far greater angles. But to retain that expectation for much larger vessels is unrealistic in the real world.

 

[Mark-1]

I don’t know what a typical angle of downflooding of a ship is.

Nor me and Google was unhelpful but you only have to look at a ship to determine roughly which permanently open openings would be submerged at 40 degrees and the answer for the 'normal' ships we see around the UK coast the answer is none.

 

[Mark-1]

The MAIB report says 15 seconds, so if that turns out to be correct, then, as suspected, downflooding didn't likely cause this :

What happened to the Bayesian? First official report reveals events on night of fatal sinking - Yachting World