Atlantic 57 Catamaran Capsized

[Just Another Sa]

Originally Posted by Dockhead

That a ballasted keel monohull cannot be inverted by wind alone is an uncontroversial fact, widely accepted by mono sailors and cat sailors alike.

Not all "uncontroversial facts" are actually true -- sometimes there is one lone genius knows something that the mass of the rest of us do not.

But if you are the lone genius who understands what all the rest of us do not -- the burden is on you, to cite your facts or make your arguments. You have not done that. Where is the "science and engineering"? I see nothing but bald assertions.

A lone genius???
Of course not, it's a basic fact known by all that have studied boatdesign.

[fatherchronica]

I was in Minnesota 23 years years ago and we went to see where a microburst had swept down a canyon for 3 miles with what the paper said were 300 mph winds. For a half mile wide every tree was laying flat oriented with the wind direction. I am confidant that that kind of blast, essentially from nearer zero than to the 300 mph upper end would roll my heavily ballasted full keel to beyond 90 degrees. The only difference between my boat and a multi hull is that mine would come back upright and the multihull would not. It is the essential reason I did not feel the need to install an escape hatch in the hull. There was a guy at the beginning of this thread who had high performance cars and had sailed his cat down wind in something like 40 kts and 6' seas and felt that was proof his multihull was super stabile. But went on to say he chose what conditions he sailed in. That is awesome for him to have that ability. I do not. I try. But have failed to the point of sailing into 25' breaking seas in 55 kts of sustained winds for many hours. I would have been truly terrified in a multihull, and I used to be the helmsman on a racing multihull. To tell the truth, I was often terrified of that boat in 25 kts of wind. I couldn't figure out how relatively thin plywood could be submerged and slamming into seas and not come to pieces

[Dockhead]

Originally Posted by Just Another Sa

A lone genius???
Of course not, it's a basic fact known by all that have studied boatdesign.

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.

[boatman61]

Originally Posted by neilpride

You forgot to add the underwear hanging in the lifelines, 2SQ inch to the maths....

Budgie smugglers.. 1sq inch..

[boatman61]

Originally Posted by fatherchronica

I was in Minnesota 23 years years ago and we went to see where a microburst had swept down a canyon for 3 miles with what the paper said were 300 mph winds. For a half mile wide every tree was laying flat oriented with the wind direction. I am confidant that that kind of blast, essentially from nearer zero than to the 300 mph upper end would roll my heavily ballasted full keel to beyond 90 degrees. The only difference between my boat and a multi hull is that mine would come back upright and the multihull would not. It is the essential reason I did not feel the need to install an escape hatch in the hull. There was a guy at the beginning of this thread who had high performance cars and had sailed his cat down wind in something like 40 kts and 6' seas and felt that was proof his multihull was super stabile. But went on to say he chose what conditions he sailed in. That is awesome for him to have that ability. I do not. I try. But have failed to the point of sailing into 25' breaking seas in 55 kts of sustained winds for many hours. I would have been truly terrified in a multihull, and I used to be the helmsman on a racing multihull. To tell the truth, I was often terrified of that boat in 25 kts of wind. I couldn't figure out how relatively thin plywood could be submerged and slamming into seas and not come to pieces

This was the UK in 1987 after some 115kt October winds... a wood in Suffolk.

[Polux]

Also interesting information regarding the negative impact of fixed keels regarding capsize on breaking waves:

"The addition of the keels appeared to result in a slight increase in the vulnerability to capsize. For the narrow model it increased the capsize incidence from 14% to 60%, and for the standard model with the second VCG increase it increased from 17% to 25%"
http://www.wumtia.soton.ac.uk/sites/...STAB2000BD.pdf

However I disagree that a 14 to 60% in a case and 17 to 25% on another can be called as a "slight increase". It looks to me a significant increase.

[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

[Polux]

Not knowing what really hit the Atlantic 57 it seems to me that there has been here a devaluation of what a squall is and his possible consequences. A squall implies at least a sudden increase of the average wind by 16k, they can reach +22k and not frequently, over that. They are normally associated with a sudden wind direction and have a short duration, typically about a minute.
http://www.skymetweather.com/content...thundershower/


If I remember correctly they were sailing with about 20k, going upwind and if they got an increase of 22K, the wind increased suddenly to 42k, a more than 2 times increase.

And since they were close on the wind a sudden change of direction can quite possibly have brought suddenly a more than two times stronger wind to a beam direction. With the sails tight for upwind sailing, that would have added greatly the consequences of being hit directly by a wind hall two times stronger than what they where sailing in.

[neilpride]

Paolo, the sails are ease for dinner... not tight . Mainsail and staysail,...

[Polux]

Originally Posted by neilpride

Paolo, the sails are ease for dinner... not tight . Mainsail and staysail,...

Yes they were eased but they were still sailing upwind. What can be eased, maintaining course, is limited by flogging.

[neilpride]

Originally Posted by Polux

Yes they were eased but they were still sailing upwind. What can be eased, maintaining course, is limited by flogging.

You can move the traveler outboard and still get some grip in the sails, or just let the sails flog a bit until dinner is done..

[44'cruisingcat]

Originally Posted by CookiesnTequila

I have a trick question for all you children. Why is it that I never see cat owners start a catamaran/mono pissing matches when a mono sinks or is lost?

Makes me wonder too. Maybe we're confident in our choice of boat, and don't feel the need to deride those who've chosen differently?

Or maybe we just have better manners.

[smj]

Originally Posted by Polux

Yes they were eased but they were still sailing upwind. What can be eased, maintaining course, is limited by flogging.

They also had a reefed jib and double reefed main.


Sent from my iPhone using Cruisers Sailing Forum

[Factor]

Originally Posted by Polux

Not knowing what really hit the Atlantic 57.

Hasnt stopped you posting incessantly about what happened to it and big wave rider

[robert sailor]

Sailors have their insecure moments, every time there is an aircraft accident the review board would send out their final reports to all licensed pilots so we could all learn from others mistakes, I say mistakes because in almost all cases the accidents came from mistakes but from time to time it was a structural failure. We didn't give a damn whether it was an aircraft made by the same manufacturer as one we may have owned because we wanted to learn from real world failures. Why is it that sailors seem to take all this stuff personally and feel a need to constantly support their personal choices instead of having a desire to learn from others??