Bayesian Interim Report

[Mister E]

Yachts are absolutely designed to survive a knockdown, I've been knocked down on a Summer's day in Poole Bay and seen dozens of boats knocked down in normal use. A yacht doesn't care if it's knocked down in a freak downdraft under bare poles or due to crew error with the kite up in a Sunday afternoon race. Either way it doesn't sink fast, and it comes back up. (As we can see in the video posted above.)

...and a yacht is far less prone to wind damage from these extreme events than a building - I've never seen the roof blown off an AWB.

You have never seen a video of a yacht having a direct hit from a tornado.

 

[Mark-1]

Aren’t you trying to compare apples and pears though?

Not in that post, no.

 

[Mark-1]

You have never seen a video of a yacht having a direct hit from a tornado.

There's a video of a yacht being hit by a similar weather event to the one suspected of sinking the Bayesian in this thread, that's the video I'm referring to.

 

[westernman]

You have never seen a video of a yacht having a direct hit from a tornado.

There is a video in post #424.
The yacht (a catamaran) in question is actually flying.

 

[Mister E]

There is a video in post #424.
The yacht (a catamaran) in question is actually flying.

Yes I was wrong about the video.
A tornado is not always just a knock down as the video shows.
Until the boat is raised we don't know what damage was done to hatches windows and the rest due to the forces involved.
I still maintain the no yacht is designed or made to withstand the forces the can break concrete.

 

[ylop]

Anyone anchoring in the Med with thunder cells about ?

Now it might be that anyone anchoring in the med with thunder a possibility SHOULD be preparing for hurricane force gusts and knock down. I’ve never sailed there, but I don’t recall anyone proposing this was normal here, YouTube, in magazine or books I’ve read etc. There may be a learning point here, about just how significant those winds can be, and what the consequences might be.

Why do you say there’s information missing from the stability book? There have been no findings that said as much as far as I can read. There may be stuff missing that people think should have been there, but a stability book is a document that needs to be approved by a certified authority. It must have been approved. And why do you say it is an unusually unstable vessel? It met all the stability requirements

I’d suggest that’s a lawyers answer! “My documents were all compliant and signed off” is different from “My documents provided the owner and captain with the information they need” is not actually the same thing. I would expect we might see recommendations on stability books to contain extra info as a learning from this.

 

[DFL1010]

Are you saying Offshore Supply Boats have unsealable openings that are submerged at 40 degrees? I can't see any. I've never seen one first hand I've googled and they look like massive flat bed trucks and it all looks sealed to me up to the bridge. Looks to me like a giant could grab it, submerge it up to the bridge and it would just bob back up. Which is what you'd expect given their role.

I'd strongly suggest not being onboard if you tried that, because that's completely not what would happen.

 

[Mark-1]

I'd strongly suggest not being onboard if you tried that, because that's completely not what would happen.

Now I'm intrigued. What would happen? Crushed by water pressure? Or are you saying there *are* unsealable openings fairly low down and it would sink fast?

 

[boomerangben]

Are you saying Offshore Supply Boats have unsealable openings that are submerged at 40 degrees? I can't see any. I've never seen one first hand I've googled and they look like massive flat bed trucks and it all looks sealed to me up to the bridge. Looks to me like a giant could grab it, submerge it up to the bridge and it would just bob back up. Which is what you'd expect given their role.

It depends on the definition of angle of downflooding, which according to the MCA includes any opening, sealable or otherwise. Offshore vessels of that nature are not governed by the same rules though. I simply don’t know. All I am saying is that I question your claim that all normal ships will have an angle of downflooding of much greater than 40 degrees. It is clear from what’s available on the internet that commercial motor vessels (ie ships normal or otherwise) can have a angle of downflooding of less than 40 degrees providing the GZ curve meet certain parameters

 

[boomerangben]

I’d suggest that’s a lawyers answer! “My documents were all compliant and signed off” is different from “My documents provided the owner and captain with the information they need” is not actually the same thing. I would expect we might see recommendations on stability books to contain extra info as a learning from this.

Definitely the lawyers answer. But since people died and others are opining that the boat was unsafe, I think it worth sticking to the facts at this stage. I suspect your right though, I too expect there will be recommendations relating stability books

 

[Mark-1]

It depends on the definition of angle of downflooding, which according to the MCA includes any opening, sealable or otherwise. Offshore vessels of that nature are not governed by the same rules though. I simply don’t know.

Well, google says the definition is this:

The downflooding angle is the angle at which a vessel heels (leans) where an opening that is not weathertight will be submerged, allowing water to enter. This angle is a crucial factor in assessing a vessel's stability and ability to withstand heeling.

The MCA must be bloody mental if they count sealable openings as points of downflooding. By their definition submarines and RoRo ferries both downflood bolt upright in normal use!

You brought "Offshore Supply Boats" up, not me.

 

[Fr J Hackett]

The biggest "sealable opening" and I will guess for whatever reason it was open when the yacht went past its AVS and DFA were the large glass doors leading to the aft saloon. Such doors have a habit of overriding their latches in even moderately bouncy seas.

 

[franksingleton]

Now it might be that anyone anchoring in the med with thunder a possibility SHOULD be preparing for hurricane force gusts and knock down. I’ve never sailed there, but I don’t recall anyone proposing this was normal here, YouTube, in magazine or books I’ve read etc. There may be a learning point here, about just how significant those winds can be, and what the consequences might be.

We had 10 years in the Med, 2000 to 2009. We saw some pretty vigorous storms. On one day in the Balearics we saw 3 waterspouts.We were uncomfortably near one crossing the Ebro delta. We had some fairly hairy nights. There was little out of the ordinary in the forecasts. A forecast of isolated thunderstorms (temporale isolate) used not to worry us until on hazy day with poor visibility, one came out of the blue, gave one lightning strike so near that we heard the crackling due to ionisation. A very close call but we saw and heard no others on that day.
The combination of warm water, hot land and topographical effects can conspire to give dangerous, unpredictable weather. A scale or two up, there are Medicanes. These are becoming more frequent and more severe due to global warming.
No doubt, there are many more microbursts, supercells or whatever you call them, than are ever reported because of their small size and limited duration.

 

[penberth3]

....The MCA must be bloody mental if they count sealable openings as points of downflooding....

An unsealed or leaking "sealable opening" will obviously allow water ingress. It's a potential route for downflooding that shouldn't be ignored.

 

[RunAgroundHard]

An unsealed or leaking "sealable opening" will obviously allow water ingress. It's a potential route for downflooding that shouldn't be ignored.

The reason it is not considered, like pilot doors on the side of the ship, or space ventilation grills covered with weather tight hatches, is that the sealing arrangements and maintenance, inspection of the seals and dogs, including the standing orders are all in place and checked at time of class inspection, periodic inspection. That is why they are not included in the calculation, because the sealing ability has been designed in and is assumed to be maintained and ready for operation when the designated conditions are expected, or shut when at sea. This latter point is not always possible, hence the marine manual will state the conditions they have to be dogged down. The classification society expects surveyors to check maintenance and inspection of such items at periodic inspections. At time of design, stability requirements do not assume that the hatch fails and that the seals are not maintained, dogs are incapable of locking down, and that the hatch hinges have seized up. Water tight doors are designed with failure in mind and are a totally different set of rules and operational procedures i.e. always closed at sea.

 

[Mark-1]

.

 

[Mark-1]

The reason it is not considered, like pilot doors on the side of the ship, or space ventilation grills covered with weather tight hatches, is that the sealing arrangements and maintenance, inspection of the seals and dogs, including the standing orders are all in place and checked at time of class inspection, periodic inspection. That is why they are not included in the calculation, because the sealing ability has been designed in and is assumed to be maintained and ready for operation when the designated conditions are expected, or shut when at sea. This latter point is not always possible, hence the marine manual will state the conditions they have to be dogged down. The classification society expects surveyors to check maintenance and inspection of such items at periodic inspections. At time of design, stability requirements do not assume that the hatch fails and that the seals are not maintained, dogs are incapable of locking down, and that the hatch hinges have seized up. Water tight doors are designed with failure in mind and are a totally different set of rules and operational procedures i.e. always closed at sea.

And if you count sealed openings as openings for the calculation of downflood angles then you end up with perverse and meaningless numbers. Any vessel (like the Bayesian) with an opening at the waterline has a downflood angle of 1°.

Personally, I don't believe the MCA do it that way but I can't be bothered to check.

 

[penberth3]

So what?

So the MAIB is not "bloody mental" (your words) to include these openings.

 

[Mark-1]

So the MAIB is not "bloody mental" (your words) to include these openings.

The poster said MCA, not MAIB.

....and no, I'm pretty sure the MCA are not.

EDIT: As you know, the MAIB used a calculation consistent with the "sane" one, because they came up with just over 40° which looks correct to me.

 

[Graham376]

Update