Atlantic 57 Catamaran Capsized

[arsenelupiga]

Originally Posted by Polux

On topic again. I had a look at the hulls of those chamberlain 14 and TS 52 that have a percentage of capsizes even higher than the ones of the Atlantic 57 and they don't have those small fixed keels so I guess that the high percentage of capsizes on the Atlantic 57 it is not related with the keels.

But fact is that Catanas and Outremer, even if both have experienced capsizes, have a lot more boats on the water and the percentage of capsizes is much, much smaller. I will try to look at the differences in design namely if the sail area/displacement are similar or if there are any difference that stands for that much superior safety record in what regards capsizes.

maybe french play more with wind tunnels. To my surprise, my fat lagoon tacks EVERY time without problem. This was not the case with some not that much older cruising/performance cats i was testing.

[Factor]

Originally Posted by Polux

Sometime it is difficult to understand you.

The feeling is mutual.

[donradcliffe]

Originally Posted by arsenelupiga

one can release sheet in <2 seconds if stand by which i understand someone was. Knife even faster. There is no way wind can come from 20 to 100 in less than 2 seconds as air acts like fluid and disturbances/accelatrations will be felt earlier.

why noone believes cat was capsized due to hull tunnel & light weight combination ? Looks like 100 Kn in right direction will do the trick if heavy lagoon can be done in 150.

I have experienced sudden wind changes, but so far they were always preceded by sudden temp changes, or unusual colours or moisture.

Someone mentioned enclosures separate from outside - alter temp perception and plastic windows alter visibility.

I really like the looks of the Atlantic 57, except for the forward cockpit, which really can contribute to accidents. Take a look at the videos of the Vendee Globe leaders in the Southern Ocean

https://www.youtube.com/watch?v=Aks2...ature=youtu.be

There is no way you would be on watch in a forward facing cockpit in those conditions, and these boats are going downwind.

[transmitterdan]

Originally Posted by arsenelupiga

one can release sheet in <2 seconds if stand by which i understand someone was. Knife even faster. There is no way wind can come from 20 to 100 in less than 2 seconds as air acts like fluid and disturbances/accelatrations will be felt earlier.

why noone believes cat was capsized due to hull tunnel & light weight combination ? Looks like 100 Kn in right direction will do the trick if heavy lagoon can be done in 150.

I have experienced sudden wind changes, but so far they were always preceded by sudden temp changes, or unusual colours or moisture.

Someone mentioned enclosures separate from outside - alter temp perception and plastic windows alter visibility.

I think you would be surprised how fast wind speed can increase when encountering a cyclone/tornadic cell. It can jump up very fast and often much faster than a normal person can react. Absent an accompanying water spout these things are often impossible to see coming after dark. And by the time the wind reaches 50 knots it's too late to react because it can top 100 knots a second later. It's just bad luck to be caught out close to one of these things. Thankfully these events are still pretty rare. Many more boats are lost to things we can actually control such as poor maintenance and poor seamanship.

[Polux]

Originally Posted by donradcliffe

I really like the looks of the Atlantic 57, except for the forward cockpit, which really can contribute to accidents. Take a look at the videos of the Vendee Globe leaders in the Southern Ocean

There is no way you would be on watch in a forward facing cockpit in those conditions, and these boats are going downwind.

Racing boats are different since they are lighter and have proportionally more sail area but in what regards what you say, going fast alone not taking care of the sails all time, in what regards multihulls (as well as monohulls) it is a question of size and stability (given adequate and good design).

In what regards monohulls they ended up with 60ft monohulls for that type of racing because it was the ones that ended up showing an adequate stability. On multihulls, regarding circumnavigations and several capsizes with smaller boats they ended up with 100ft boats that offer an adequate stability for solo sailing and circumnavigation non stop races or records.

Right now this one is attempting to beat the absolute circumnavigation record and so far so good:

https://www.youtube.com/watch?v=nciYXXGb9_c

Incredible feat, being able to sail such a moster on a circumnavigation solo. Few guys in the world can do that and Covile is one of them.

[Just Another Sa]

Originally Posted by Polux

Yes, you are right about laws of physics. Two members on this thread said that they were caught by microbursts and described their experiences and the way the boat was knocked down and come up after that.

Some posts back another captain was describing what happened to a a big Swan caught in a micro burst and you even have posted a video of monohull caught by a waterspout, being knocked down and raising after the wind becomes less strong.

It has nothing to do with the intensity. When the boat is knocked down it offers to the wind the rounded hull and a small surface. The boat at 90º is far away from the inversion point, that in most cruising boats happens only with more 25 to 35º of heel.

The boat at 90 º has still a considerable RM and is making a lot of force to right itself up. Very small rotating force will be provided by the wind on the rounded hull surface and the wind will just be moving the boat laterally.

The fact is that there are many examples of boats knocked down to 90º by the wind in weird metereological phenomena but there are no record of any being inverted. Of course I am talking about Class A boats, but then almost all boats out there on the Ocean are class A boats.

Anyway we are not discussing monohulls here.

A monohull at 90 degrees heel does not have a small surface, neither a small drag cofficient if true wind angle is 90 degs. Aerospaceweb.org | Ask Us - Drag of Cylinders & Cones
Near end of the page linked you will find a table with a headline: "Drag coefficients of several simple 3D and 2D shapes"
Case 15) is the closest one with a monohull under given situation with Cd=1,6.
The smaller the boat is, the less rightningmoment it typically has relative to it's cross sectional area in said situation. In other words, a 10 ft wide, 30ft long boat has far less than 1/12 RM of a 20 ft wide 80ft long monohull, which it would need to make up the difference in area. Hence that 10ft wide will invert 180 degs in substantially less wind.

The boat will indeed move laterally, and while doing that it has more area under water to trip it over than a minikeel of a multi of similar size, hence it is more likely to so.

Furthermore, not all microbursts are the same, their windspeed has a very large variation, some might have more than 200 knots, not present in any video or quoted experience, which might had only 50 knots. That means 16 times greater windpressure even if the density would remain the same, which it does not. Take into account all the liquid water within the airflow moving at the same speed, and the windpressure can be easily 100 times greater, particularly down low where the exposed hull bottom is. That means over 30 000 Pa of dynamicpressure. Multiply by drag coefficient and cross sectional area and you get the force (above one million Newtons). Multiply again by vertical distance of lateral area and center of windage and you get the heeling moment (1.5 million Nm for a 30 footer). There is no 30 footer around capable of developing RM at 90 degs to match or exceed that.

The fact is that there are many examples of boats knocked down to 90º by the wind in weird meteorological phenomena but there are no record of any being inverted is due to too things, in most cases the wind was not anywhere near maximum meteorologically possible and for the rest the evidence is no longer present to make any records as the boats sink without a trace.

[Just Another Sa]

Originally Posted by Polux

It seems that not all know that a monohull (class A) cannot be inverted by wind alone and I was responding to someone that said it could.

All boat can sink including cats even if cats ten to float more when inverted. I believe all know that.

Any vessel can be inverted by wind alone, be it a monohull sailboat, a multihull, or a large ship.
Lucky for us sailors, such an event is extremely rare.

No boat having constructed from material with a density less than water can sink, regardless how many hulls such a boat has.

It's all just elementary physics, thus there is no point claiming otherwise like you do.

[Just Another Sa]

Originally Posted by Jim Cate

Frankly,this is simply wrong, unless the ballast keel has fallen off. The righting moment of the keel is quite effective when at 90 deg, there is little surface exposed to the wind and it is in a somewhat low drag shape.

You say that just because it has never happened in the known history of yachting is no proof that it can't happen... a telling argument...NOT!

Your credibility has taken a big hit with this one...

Jim

There is no evidence that it has never happened. There are cases of boats going missing without a trace.
A knocked out mono is a blunt object to the wind, not a low drag as you falsely assert. Furthermore, the exposed hull area is not small neither. It's very close to maximum possible at 90 degrees heel.

Aerospaceweb.org | Ask Us - Drag of Cylinders & Cones

Your understanding of elementary physics is lacking based on your statements above.

[Dockhead]

Originally Posted by Just Another Sa

Any vessel can be inverted by wind alone, be it a monohull sailboat, a multihull, or a large ship.
Lucky for us sailors, such an event is extremely rare.

No boat having constructed from material with a density less than water can sink, regardless how many hulls such a boat has.

It's all just elementary physics, thus there is no point claiming otherwise like you do.

Umm, elementary physics say on the contrary that ballasted keel monohulls cannot be inverted by wind alone, as several people here have correctly stated in this thread, at least within the wind range which actually occurs on Planet Earth.

That's because if a ballasted keel monohull has been knocked even flat by a huge blast of wind, it still has positive righting moment.

[Dockhead]

Originally Posted by Just Another Sa

There is no evidence that it has never happened. There are cases of boats going missing without a trace.
A knocked out mono is a blunt object to the wind, not a low drag as you falsely assert. Furthermore, the exposed hull area is not small neither. It's very close to maximum possible at 90 degrees heel.

Aerospaceweb.org | Ask Us - Drag of Cylinders & Cones

Your understanding of elementary physics is lacking based on your statements above.

Why don't you run some numbers and show us that the inverting moment caused by x knots of wind on some sailboat exceeds the righting moment at 90 degrees of heel?

You will see that you cannot reach the degree of heeling/inverting moment needed to overcome the righting moment, for any given sailboat you can think of, as long as it has a ballasted keel. Maybe conceivably with 1000 knots of wind, but not with winds experienced on Earth.


Jim and Polux are correct on all points, and in particular Jim is correct to say that a knocked-down sailboat hull will not generate much inverting moment. It is quite low drag as presented to the wind (blunt object??), but more importantly, there is very little lever arm between the center of aerodynamic resistance and the center of buoyancy. The upright rig, even without sails up, produces a great deal of heeling/inverting moment when presented to a strong wind, because the force is imparted on a long lever arm. But this goes away as the boat goes over.

[Polux]

Originally Posted by Just Another Sa

A monohull at 90 degrees heel does not have a small surface, neither a small drag cofficient if true wind angle is 90 degs. ....
The smaller the boat is, the less rightningmoment it typically has relative to it's cross sectional area in said situation. In other words, a 10 ft wide, 30ft long boat has far less than 1/12 RM of a 20 ft wide 80ft long monohull, which it would need to make up the difference in area. Hence that 10ft wide will invert 180 degs in substantially less wind.

....

You continue to insist on this again all logic. Even cat sailors said on this thread you are wrong. I can only point the flaws in your reasoning, besides the most evident flaw, that is that never happened not even when the boat is at anchor sustaining hurricane winds.

But I am confused, with your example regarding Righting moment at 90º heel, when the boat is not catching any wind on its sails. The RM of a small 30ft class A monohull will be much more than the one of a multihull on the same situation since the multihull would have 0 RM long before that angle.

Another factor here is that it is not the absolute righting moment but the R/M versus the weight of the boat that counts, and regarding the wind, the surface and angle of the wind incidence. Besides the fact that a multihull has 0 RM at 90º, the weight of a 80ft long cat is much more than the one of a 30ft monohull as well as the surface the boat offers to the wind when capsized.

Anyway the only multihulls that I know of that have capsized with arount that size are light racing boats. I don't know of any 80ft crusing multihull that had capsized with wind alone or otherwise.

[boatman61]

I'm in the camp that believes that wind alone can knock a boat flat.. however to complete the 90>>180 it needs the assistance of wave action to invert the boat.
My gut tells me the keels weight way compensates with the loss of topside windage when your knocked flat.. and without further assistance (waves) it will lay there at around 70degrees till the pressure eases. resistance is at least halved by the curved and tapering 50% of beam hull form.. unless it flat bottomed and a lift keel... or a Cat.
Also initial resistance of sails hitting the water acts as a brake..
Suffered a couple of knockdowns over the years but never 360'd.. yet..

[Just Another Sa]

Originally Posted by Polux

You continue to insist on this again all logic. Even cat sailors said on this thread you are wrong. I can only point the flaws in your reasoning, besides the most evident flaw, that is that never happened not even when the boat is at anchor sustaining hurricane winds.

But I am confused, with your example regarding Righting moment at 90º heel, when the boat is not catching any wind on its sails. The RM of a small 30ft class A monohull will be much more than the one of a multihull on the same situation since the multihull would have 0 RM long before that angle.

Another factor here is that it is not the absolute righting moment but the R/M versus the weight of the boat that counts, and regarding the wind, the surface and angle of the wind incidence. Besides the fact that a multihull has 0 RM at 90º, the weight of a 80ft long cat is much more than the one of a 30ft monohull as well as the surface the boat offers to the wind when capsized.

Anyway the only multihulls that I know of that have capsized with arount that size are light racing boats. I don't know of any 80ft crusing multihull that had capsized with wind alone or otherwise.

This:" it is not the absolute righting moment but the R/M versus the weight of the boat that counts"
is totally wrong and dangerously so. RM vs weight is totally irrelevant.
What matters is RM vs HeelingMoment. That means bigger monos are substantially better than smaller monos regarding wind induced inversion.

That was the only statement that contradicted anything I wrote. Therefore I conclude you did not point the flaws in my reasoning, as there was none.

It seems your are trying to disprove a statement I never made. I never claimed that a multihull can not be inverted by wind alone, instead I claimed all vessels can be inverted by wind alone.

[Polux]

Originally Posted by Just Another Sa

... I never claimed that a multihull can not be inverted by wind alone, instead I claimed all vessels can be inverted by wind alone.

Except that never happened to a class A boat. Maybe you are talking about sailing in Jupiter where I agree that there are probably winds strong enough not only to invert a 30ft monohull but to lift it off and blow him away in flying mode.

[Just Another Sa]

Originally Posted by boatman61

I'm in the camp that believes that wind alone can knock a boat flat.. however to complete the 90>>180 it needs the assistance of wave action to invert the boat.
My gut tells me the keels weight way compensates with the loss of topside windage when your knocked flat.. and without further assistance (waves) it will lay there at around 70degrees till the pressure eases. resistance is at least halved by the curved and tapering 50% of beam hull form.. unless it flat bottomed and a lift keel... or a Cat.
Also initial resistance of sails hitting the water acts as a brake..
Suffered a couple of knockdowns over the years but never 360'd.. yet..

How much sail area your boat has?
How much area your boat has at 90 degrees heelangle at 90 degrees twa?

The result is most likely less than 3, if not let as know what boat you have and it's dimensions.

Then compare the distances from the center of effort of sailplan to lateral resistance and the same for the hull at 90 degrees heel. The former is most propably about 3...4 times as large. And the windspeed to produce the same heelingmoment is therefore about 3...3.5 times. (squareroot of 3 times 3...4)

That means that if 30 knots will knock your boat to 90 degs with full sails, 90...105 knots on the hull alone do the same and continue to invert a 30ft boat. A bigger boat can have higher windpeed than 30 knots to knock it over, even 60 knots for a big cruising monohull, and be thus much more tolerant for windinduced inversion.
Yet windspeeds can exceed 200 knots and contain a lot of water in the air down below where your hull is, hence 10 times the windpressure compared to calculated 90...105 knots with no water that is needed to keep 30 ft boat going to full inversion.