Bayesian Interim Report

[ylop]

I haven't read many MAIB reports but the ones I have, have been interesting in that they deal with facts.

I think the key thing is they try not to assign blame, and often look beyond the basic cause (it was too windy!) to get to the underlying things which need to change to stop it happening again.

How many do?

Well I believe all superyacht captains will have sat an exam that considered GZ curves at some point (as I understand it), but clearly that doesn’t prove understanding - and MAIB had to pay a university to model it so it’s not like working out the right scope.

Are you aware of the traction limitations of your tyres at every stage of ware

No, I am aware that they get worse (in the wet) as they wear. I am aware there’s a legal minimum and that even before they hit that min they are not as good as new. I know that the way I drive with tyres in the condition I typically have I don’t get traction issues. If I was a racing driver I would be more focussed on that. If roads didn’t have speed limits and sharp bend warning signs I might be much more focussed on the limits. I think that was essentially my point - if you dont think you are operating close to the limit you don’t need to worry about the exact boundary.

It's how lessons are learnt, isn't it?

Yes, but we seemed to be moving away from “what can we learn to avoid this” to “I would never have made that mistake”.

 

[Chiara’s slave]

Interestingly the MAIB refer to a “motoring condition” with the keel up - so presumably that is considered fairly normal on such boats? I expect the reduced drag has a significant difference of fuel cost on something that bunkers by the ton rather than the litre. I guess none of us have much experience of actually sailing a superyacht but that it spends most of its life motoring except when conditions make for fun comfortable sailing? The keel in the “ready to sail” position would therefore be part of getting ready to said rather than just going to sea unless the captain understood the stability information that the designed and builder had never provided and the regulator hadn’t asked for.

Without wanting to start a spat your argument that you are “well aware” of your numbers would have been more convincing if you had actually stated the windspeed where beam on you were at risk of flipping (without looking it up). Knowing the data is there and being well aware of it, are slightly different. The data is also in the “as supplied” form - stick a liferaft on deck, a sprayhood up, or a big radar reflector 2/3rds of the way up the mast and things will be different. Our foam luff Genoa doesn’t pack as neatly as the original so we will have more windage high up than the Builder ever imagined.

And yet if a newbie asked here for pros and cons of lift keel I think many would say access to shallower anchorages was an advantage of lifting keels. Perhaps I’ve missed it, I don’t read every thread, but I don’t recall anyone saying: you might end up beam on at anchor and being knocked down. That feels like being smart after the event - I assume many sailing super yachts are reviewing their SOP right now. I wonder how many already had a rule that the keel should be down at anchor in forecast F4-5 conditions, never mind the F1 it was when they anchored.

I’m sure that, had the designers given the limitations of keel up, crew would take it into consideration. Whether they would have considered a precaution like that necessary in this case, well, they will from now on.
Our actual numbers, yes I do lnow what it says in our handbook, I have read it and remembered it. I just didn’t think it was relevant, we are a 30ft B classification trimaran, not a competing superyacht. The principle is the same, of course.

 

[Fr J Hackett]

Something that occurred to me as a question, do yachts (12M plus) with lifting keels and centreboards publish AVS for both keel up and down and what's the difference if they do. Considering the large numbers out there from some old US Aldens to the more modern Southerlies and now Boreals and Garcias if they don't will the manufacturers and designers be issuing new information.

 

[billskip]

Yes, but we seemed to be moving away from “what can we learn to avoid this” to “I would never have made that mistake”.

If life were that simple there wouldn't be any mistakes.....
Whenever the human factor is involved there is risk...
You are not making allowance for "rules are made to be broken/ignored " .."it'll be ok dont worry about it" ... "this boat is unsinkable "

"Lessons only need to be learnt by those othe than me"

 

[DreadShips]

To defend the skipper, it's a commercial vessel (although on reflection I'm not sure of the exact legal position, but it's certainly being run like one) Whether the keel is up or down is going to be whatever the SOPs say, not whether he has a funny hunch based on numbers he doesn't have.

 

[billskip]

Something that occurred to me as a question, do yachts (12M plus) with lifting keels and centreboards publish AVS for both keel up and down and what's the difference if they do. Considering the large numbers out there from some old US Aldens to the more modern Southerlies and now Boreals and Garcias if they don't will the manufacturers and designers be issuing new information.

I seem to recall it being said (officially or not?) That the boat was capable in both up and down configuration.
However I've not read anything with reference to a tornado crossing its decks.

 

[Fr J Hackett]

I seem to recall it being said (officially or not?) That the boat was capable in both up and down configuration.
However I've not read anything with reference to a tornado crossing its decks.

Which is nothing at all to do with the question I posed

 

[billskip]

To defend the skipper

Afraid the skipper will always be found liable in some way, it's self preservation by those above and insurance companies.

 

[billskip]

Which is nothing at all to do with the question I posed

Only because your being selective with the answer you want.
In this instance I believe (I could be wrong) that the maib report stated that certain information, that I believe you are referring to, was not available.

 

[Fr J Hackett]

Only because your being selective with the answer you want.
In this instance I believe (I could be wrong) that the maib report stated that certain information, that I believe you are referring to, was not available.

If you read, I know it might be something of a challenge for you but my question was about the large number of small ie 12M plus lifting keel / centreboard yachts from a variety of manufacturers and how if they report AVS it is nothing to do with Bayesian or the MAIB report except that it is what prompted the question.

 

[flaming]

Something that occurred to me as a question, do yachts (12M plus) with lifting keels and centreboards publish AVS for both keel up and down and what's the difference if they do. Considering the large numbers out there from some old US Aldens to the more modern Southerlies and now Boreals and Garcias if they don't will the manufacturers and designers be issuing new information.

I know that on an old “AWB vs MAB” thread I posted some stability curves for a pogo that had both. I have no idea if that’s the norm or just because the Pogo’s were good and they wanted to publicise them though.

 

[DreadShips]

A further question, having never had cause to think about it before, is there anything anywhere to tell most yacht owners what windspeed will lay their boat over under bare poles? Stability curves are great and all, but odd stuff happens as the forces go up (witness Bayesian, where the mast was generating significant amounts of lift - about 20% of the total force iirc)

 

[flaming]

Possibly being the magic word, there are some designs that retain main mast hight with or without a mizzen.

I might be misremembering but doesn’t the Baysean have sisterships that are ketches, and don’t they have smaller rigs?

The fact that some other designs might do that, probably doesn’t have all that much relevance to a design that was pretty extreme in its dimensions.

 

[ImpImp]

Why has this thread degenerated into a bitchfest worthy of a group of Lower 5th girls? Come on chaps, grow up, it is quite a serious subject after all. Otherwise I can see what could be an informative tread disappearing pretty quickly.

 

[Bouba]

For some perspective....the Cutty Sark doesn’t have a fin and it’s main mast is 47 m....the Bayesian with the fin up (or down) has a 75 m mast. That strikes me as a huge difference

 

[billskip]

I know it might be something of a challenge for you

Which only goes to prove you knowledge is somewhat limited..
I doubt many if any reading this thread has the answer you are looking for without actually doing searches for that information the answer to your question could simply be "yes" and "the difference is different depending on design characteristic."...which I presume (it's dangerous to presume here) you are capable of.

 

[billskip]

Why has this thread degenerated into a bitchfest

Human nature, common reason for loads of stuff.

 

[billskip]

I might be misremembering but doesn’t the Baysean have sisterships that are ketches, and don’t they have smaller rigs?

I believe this to be correct.

The fact that some other designs might do that, probably doesn’t have all that much relevance to a design that was pretty extreme in its dimensions.

Extreme design should surely not be at the expense of ultimate safety.
However how does one design something to protect it from unknown conditions?

Imho the keel up will be the judgemental factor here, but will never be any absolute proof being down would have prevented the result.

 

[flaming]

I believe this to be correct.

Extreme design should surely not be at the expense of ultimate safety.
However how does one design something to protect it from unknown conditions?

Imho the keel up will be the judgemental factor here, but will never be any absolute proof being down would have prevented the result.

Yes agree.

 

[E39mad]

My understanding is that the Perini Navi manufacturers documents (manual) state that the keel should be lowered in offshore sailing conditions and can be raised for motoring purposes. The keel is a centreplate which is housed in a ballasted keel box.

Surprised there has been little mention of the down flooding angle - which I understand to be about 45 degrees due to open (generators and air con running) air vents in the rear of the hull and possibly the lowering steps into accommodation along the side decks