Atlantic 57 Catamaran Capsized

[Seaslug Caravan]

Originally Posted by Polux

A performance cruising boat like the Chamberlain 14 is a compromise between performance and cruising amenities.

Appologies if this has already been posted

Yes , the chamberlain 14 would make an interesting case study as 2 that I know of have capsized, (Big Wave Rider (discussed here recently), and Incinerator ( Devonhouse Recollections )

I am unsure of the exact number built. I know of only 3.

[smj]

Originally Posted by Seaslug Caravan

Appologies if this has already been posted



Yes , the chamberlain 14 would make an interesting case study as 2 that I know of have capsized, (Big Wave Rider (discussed here recently), and Incinerator ( Devonhouse Recollections )



I am unsure of the exact number built. I know of only 3.

Now that cat has the best of both worlds. It flips but then is self righting. On top of that it floats after self righting!


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[44'cruisingcat]

Yeah, pretty obvious that boat hasn't been floating upside-down....

[Training Wheels]

Of course not. The article said it "mysteriously righted itself". It probably did so shortly after capsizing, and then continued to float upright. The article said so, so it must be true. Perhaps it has ballasted keels?

[Just Another Sa]

Originally Posted by Dockhead

I will eat my hat if you can provide a single quotation from a real boat designer, saying that ballasted keel monos can be inverted by wind alone without wave action.

You are mistaken, sir. This is not indeed a "basic fact". In fact I would say that you just made it up.

On the contrary, the basic fact is this:

"[M]ultihulls differ from ballasted monohulls which, when at 90 degrees, have positive righting moments but negligible wind heeling moments."

http://www.wumtia.soton.ac.uk/sites/...STAB2000BD.pdf

Note the phrase "negligible wind heeling moment" when heeled at 90 degrees. That is because of the lack of significant lever arm between aerodynamic CE and center of buoyancy, of a ballasted keel monohull heeled to 90 degrees.


This is from the most extensive scientific study ever done of multihull stability, done by the University of Southampton. The same laboratory did a huge study of monohull stability a few years prior to this.


Thread drift: the same study shows that catamarans are far more resistant to wave action capsize, than monos, proved both by model studies and by accident statistics. That's more support for the proposition that mono stability and cat stability are simply different -- neither is really better or worse overall than the other.

Fine, go ask University of Southampton, everybody there in the field (=not the janitor or secretary) knows enough to inform you what would happen to a small monohull in 200 knots of winds on the beam.
After that you may eat your hat, but I don't require you to do so, it's totally up to you.
They can also confirm that same size multihull would have much greater heelingmoment at 90 degrees heeling angle, and therefore heelingmoment on the mono is indeed negligible compared to a multi. They can also conform to you that the HM of the mono at 50 knots of wind is mostly due to mast & rigging, when all sails are down and that it would have far less than 90 degs heeling angle under those conditions.

You will however have no support at all for nonsense like this :" lever arm between aerodynamic CE and center of buoyancy"
Tell that to them and they may laugh at you or behind your back.
Or they might educate you about the difference between heeling and righting moment and that those have separate levers. Hm involves aerodynamic CE and RM involves center of buoyancy.

[leftbrainstuff]

This thread is very 'War and Peace'.

It's just physics people. And physics doesn't discriminate.

With the current racing and condo inspired monohulls I suspect most of them wouldn't right themselves if knocked down.

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[leftbrainstuff]

Originally Posted by Just Another Sa

Fine, go ask University of Southampton, everybody there in the field (=not the janitor or secretary) knows enough to inform you what would happen to a small monohull in 200 knots of winds on the beam.
After that you may eat your hat, but I don't require you to do so, it's totally up to you.
They can also confirm that same size multihull would have much greater heelingmoment at 90 degrees heeling angle, and therefore heelingmoment on the mono is indeed negligible compared to a multi. They can also conform to you that the HM of the mono at 50 knots of wind is mostly due to mast & rigging, when all sails are down and that it would have far less than 90 degs heeling angle under those conditions.

You will however have no support at all for nonsense like this :" lever arm between aerodynamic CE and center of buoyancy"
Tell that to them and they may laugh at you or behind your back.
Or they might educate you about the difference between heeling and righting moment and that those have separate levers. Hm involves aerodynamic CE and RM involves center of buoyancy.

Be careful with over simplification. Much beloved by academia when only simple models are available. Correlation to the real world of these simple dynamic models is usually poor.

You have 6 degrees of freedom interacting during an actual knockdown. Not to mention base excitation that imposes significant reactive forces from waves.

As for 200 knots of wind. That is likely past the survivability of most boats. I've not seen any data out to 200 kts. Where did this upper limit come from?

It also reads to me like extrapolation from simple models. In 30 years I've yet to see extrapolation make any engineer the smartest person in the room.

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[Just Another Sa]

Originally Posted by Polux

I remembered this paper about a comparison of stability between different types of sailboats when they are hit by a sudden gust of wind and I believe it is relevant to this thread information.

They made a comparison between a monohull and a trimaran that carry the same sail area, being the monohull a bit longer (9.75 to 8.25) when they are sailing with a wind that causes a hell of 20º to the monohull and 12º to the trimaran and are subject to a gust 1.4 times superior to the average wind. If the wind was 20k, we would be talking about a gust with 28K.



On the bottom the references regarding the increase danger that represents for a capsize if that gust comes from a squall may be relevant to the Atlantic 57 capsize. Off course, on a boat the size of the Atlantic we would not be talking just about an increase of 1.4 but substancially more.
http://www.wumtia.soton.ac.uk/sites/...NDBOAT94BD.pdf

Quote from the picture you provided: (beginning at the end of left column)
"the product of displacement and GM for the trimaran is 5.4 tonne meters, while that for a monohull is 6.1 tonne metres.
... the monohull's righting moment continues to increase to a maximum value of 4.8 tonne meters at 80 degrees. The monohull can therefore resist a much greater maximum heeling moment than the multihull. "

Is the maximum righting moment of the monohull in question at 80 degrees heel 6.1 tonne-meters or 4.8 tonne-meters, both values claimed in the quote?
Obviously only 4.8 is correct, and the other number is pure nonsense.

Therefore the monohull can not resist a much greater maximum heeling moment as claimed, but 11% less, 4.8 tonne-meters for the mono and 5.4 tonne-meters for the multi.
It can however tolerate a higher apparent windspeed under same size sails sheeted equally.

The article contains miss-information, not limited to that quote.
It is not a peer reviewed scientific paper, but just a magazine article.

[Just Another Sa]

Originally Posted by leftbrainstuff

Be careful with over simplification. Much beloved by academia when only simple models are available. Correlation to the real world of these simple dynamic models is usually poor.

You have 6 degrees of freedom interacting during an actual knockdown. Not to mention base excitation that imposes significant reactive forces from waves.

As for 200 knots of wind. That is likely past the survivability of most boats. I've not seen any data out to 200 kts. Where did this upper limit come from?

It also reads to me like extrapolation from simple models. In 30 years I've yet to see extrapolation make any engineer the smartest person in the room.

"I've not seen any data out to 200 kts. Where did this upper limit come from?"

It's not an upper limit, but an estimate of maximum surface wind speeds that exist due to short term meteorological phenomena at 90% probability.
That means there is a 10% probability there are even higher surface winds due to those events. I got that value by asking some meteorologist how strong winds those events can produce after they discussed about it.
It's based on physical limits rather than computer models. And it represents true airspeed as aircraft pilots call it. The real effect would be based on indicated airspeed, which is substantially higher near water surface due to increased average density of air-water mixture compared to dry air.

Ps, see post 437 by @fatherchronica (300 mph winds)
Pps, you will never see measured data about wind speeds of those events, they are very rare and there is practically no chance at all there would be any reliable meteorological wind instruments nearby.

[Cottontop]

Originally Posted by Just Another Sa

The real effect would be based on indicated airspeed, which is substantially higher near water surface due to increased average density of air-water mixture compared to dry air.

Humid air is less dense than dry air, no?

[donradcliffe]

Originally Posted by Just Another Sa

Quote from the picture you provided: (beginning at the end of left column)
"the product of displacement and GM for the trimaran is 5.4 tonne meters, while that for a monohull is 6.1 tonne metres.
... the monohull's righting moment continues to increase to a maximum value of 4.8 tonne meters at 80 degrees. The monohull can therefore resist a much greater maximum heeling moment than the multihull. "

Is the maximum righting moment of the monohull in question at 80 degrees heel 6.1 tonne-meters or 4.8 tonne-meters, both values claimed in the quote?
Obviously only 4.8 is correct, and the other number is pure nonsense.

Therefore the monohull can not resist a much greater maximum heeling moment as claimed, but 11% less, 4.8 tonne-meters for the mono and 5.4 tonne-meters for the multi.
It can however tolerate a higher apparent windspeed under same size sails sheeted equally.

The article contains miss-information, not limited to that quote.
It is not a peer reviewed scientific paper, but just a magazine article.

I don't know what your agenda is, but every time you post you demonstrate that most of us have forgotten more about physics than you will ever know. The physical principles of mono's vs multii's don't change, no matter how much you misinterpret them. I could refute most everything you have said, but its not worth my while, because the reality is complex.

[Polux]

Originally Posted by Just Another Sa

Quote from the picture you provided: (beginning at the end of left column)
"the product of displacement and GM for the trimaran is 5.4 tonne meters, while that for a monohull is 6.1 tonne metres.
... the monohull's righting moment continues to increase to a maximum value of 4.8 tonne meters at 80 degrees. The monohull can therefore resist a much greater maximum heeling moment than the multihull. "

Is the maximum righting moment of the monohull in question at 80 degrees heel 6.1 tonne-meters or 4.8 tonne-meters, both values claimed in the quote?
Obviously only 4.8 is correct, and the other number is pure nonsense.

Therefore the monohull can not resist a much greater maximum heeling moment as claimed, but 11% less, 4.8 tonne-meters for the mono and 5.4 tonne-meters for the multi.
It can however tolerate a higher apparent windspeed under same size sails sheeted equally.

The article contains miss-information, not limited to that quote.
It is not a peer reviewed scientific paper, but just a magazine article.

That is not an article but a technical paper from someone that knows a lot about boat stability.

No, the paper is not wrong, it seems that what you know about the subject did not allow you to understand it.

One value is the product of the GM and displacement - 6.1 tonne meters

The other value is the maximum righting moment(4.8) that is the product of Max GZ and displacement.

By the way the author, Barry Deakin is a research engineer of the Southampton University, the one you were (rightly) referring to be a reference in what regards stability studies for monohull and multihull yachts and Naval Architecture related with them.

[Dockhead]

Originally Posted by Just Another Sa

Fine, go ask University of Southampton, everybody there in the field (=not the janitor or secretary) knows enough to inform you what would happen to a small monohull in 200 knots of winds on the beam.
After that you may eat your hat, but I don't require you to do so, it's totally up to you.
They can also confirm that same size multihull would have much greater heelingmoment at 90 degrees heeling angle, and therefore heelingmoment on the mono is indeed negligible compared to a multi. They can also conform to you that the HM of the mono at 50 knots of wind is mostly due to mast & rigging, when all sails are down and that it would have far less than 90 degs heeling angle under those conditions.

You will however have no support at all for nonsense like this :" lever arm between aerodynamic CE and center of buoyancy"
Tell that to them and they may laugh at you or behind your back.
Or they might educate you about the difference between heeling and righting moment and that those have separate levers. Hm involves aerodynamic CE and RM involves center of buoyancy.

You keep saying "everyone knows". Yet you don't provide anything with any substance to make your point. If it's so simple and obvious, can't you make a calculation or give us a citation, or give us a real life example? Every single other poster on this thread has called BS on this. I would be glad to find out that you are a lone genius with a unique understanding of how this works -- maybe we could all learn something -- but you don't give us anything to work with -- you give us only rhetoric and insults.


The paper I cited did not say that the heeling moment is negligible "compared to multihulls". It said that the heeling moment is negligible -- period. It's what all the rest of us have been saying -- knock a monohull down with a strong gust, and it will stay at 90 degrees (or 80, or 70, or whatever) until the gust passes, then it will pop back up. It will not go over in the absence of wave action. Because once the mast, rigging and superstructure is out of the wind, there is negligible heeling moment, and yet righting moment is still large.


Lever arm -- which you call "nonsense" -- is how you convert force to moment. The equation if M = F a, where M is moment, F is force, and a is arm. A certain amount of force centered up in the rigging will produce a lot of heeling moment, because there's a long lever arm. The same or even much more force, centered down at the heeled over hull, close to the center of buoyancy, produces proportionately less torque. That's why the wind can't capsize a typical ballasted keel mono, at least not in terrestrial wind ranges.

[Dockhead]

Originally Posted by Just Another Sa

Quote from the picture you provided: (beginning at the end of left column)
"the product of displacement and GM for the trimaran is 5.4 tonne meters, while that for a monohull is 6.1 tonne metres.
... the monohull's righting moment continues to increase to a maximum value of 4.8 tonne meters at 80 degrees. The monohull can therefore resist a much greater maximum heeling moment than the multihull. "

Is the maximum righting moment of the monohull in question at 80 degrees heel 6.1 tonne-meters or 4.8 tonne-meters, both values claimed in the quote?
Obviously only 4.8 is correct, and the other number is pure nonsense.

Therefore the monohull can not resist a much greater maximum heeling moment as claimed, but 11% less, 4.8 tonne-meters for the mono and 5.4 tonne-meters for the multi.
It can however tolerate a higher apparent windspeed under same size sails sheeted equally.

The article contains miss-information, not limited to that quote.
It is not a peer reviewed scientific paper, but just a magazine article.

None of this has the slightest relevance to the point.

If you don't have an actual argument, attack the source, and in this case, based on a complete misunderstanding of it.

[Seaslug Caravan]

Originally Posted by smj

Now that cat has the best of both worlds. It flips but then is self righting. On top of that it floats after self righting!


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Yes that was part of the mystery. After capsizing and being abandoned, one wonders whether wantabe salvors (commercial fishos?) had a go. certainly not hard to re-right a cat with a bit of rope and modest HP. All got to hard/bad weather/ what ever?? and it was left to continue its drift.

Wasn't Catcha that was discussed here recently after capsizing on the Wide Bay Bar also a Chambelin design ? Parrallax? maybe.

A pattern developing here maybe ?