Atlantic 57 Catamaran Capsized

[Polux]

Originally Posted by Boatguy30

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Now none of this takes into account righting moments, etc and Chris White claims that you "have" to have 100,000 lbs of righting moment to be "safe" offshore. My boat is around 70,000.
...

Let me point out what i have said many times: safety is a relative concept. One that goes for a circumnavigation in a very good and seaworthy Django 7.20 takes more risks than someone going in a much bigger equally well built and designed mono hull or cat even if proportionally cats have to be bigger to match smaller monohulls seaworthiness.

Regarding righting moment we have two situations: one the risk of capsize by waves on bare poles and regarding that a similar sized cat has more stability than a monohull of similar weight and the other regards to be capsized by wind or a combination of wind and waves and in what regards wind, that righting moment alone means nothing.

It is the proportion between the righting moment and the sail area what is relevant. Well I would have said windage, including the wind on the sails, because in cats with large cabins that will count as sail area in what regards that proportion.

[neilpride]

25000 pounds and a 78 ft tall spar, that's a beast mast ,, I try to found where the 2 reef in the mainsail is placed... I don't blame the design not even the crew but quite frankly this particular design its something to take it seriously in blustery weather ,, its not a mom and dad boat.... probably more beam or shorten the mast solve the issue or is just a matter of bad weather luck , time will tell....

[boatman61]

Seems to me the Atlantic 57 shares the same issues as the old Iroquois cats.. tall rig.. narrow beam.. maybe he should fit mast floats like the Iroquois MK1..

[catsketcher]

I used to own a Twiggy trimaran. Two different ones capsized in the early 80s (one twice). That was a large proportion of the 30 or so built. This pointed to a potential problem so the designers looked into it.

They could tell that the 30ft Twiggy was very different from normal, it had a large rig for its length and weight and was very wide, about 29ft. Could that be the issue? She also had fine bows for better speed to windward. She was designed to be sailed upwind fast and tack downwind. That was the issue.

When sailing a Twiggy on a square the large sideways stability counted for nothing, the low volume up front led the boat to assume a bow down attitude and be susceptible to pitchpoling (stern over bow capsize). All the Twiggys capsized this way. Designers learnt not to design tris with large amounts of one type of stability with much less in another direction. Sailing them, talking to the people involved and calculations led to us all learning more about trimaran design. We drilled down into the physics and added something to multi design dogma.

This is what doesn't make much sense in the Atlantic case. Let's start with one fact, Chris White designs very seaworthy looking boats. Henk de Velde who has done a huge amount of serious singlehanded miles cruised 50 000 miles in the White designed Juniper and speaks glowingly of his time sailing her. Chris White's book is first class - read it to learn a huge amount on multi design - he really pushes seamanship and safety and goes through the numbers on what makes a boat work well for cruising.

That is what has me puzzled by the Atlantic capsizes - I can't see the physics. The tall rig would be an issue IF full sail was set, but it wasn't in either case. In Leopard's case the boat was double reefed and the staysail partially furled, giving the boat a huge margin of safety. As stated before this should allow Leopard to function safely up to hurricane force winds. If she had a small rig they would have not have reefed as much so the same sail would be set. So how could she flip?

Is it stability? Boatguy talks of his boat being proportionally wider but we have to be careful here. The square cube rule means that a cat twice as long will be 16 times more stable (if all other proportions stay the same). Stability goes up by the power of four but rig force by the cube. Going bigger is undoubtedly safer, so you can make a big cat a little bit narrower proportionally than a small one and still be way safer. I don't think it is stability, the Atlantics have huge stability.

(Boatguy - slow down man - If you are lifting the windward hull 18 inches you are about to fly it. That is your maximum stability right there. So you have already found it, it's around 35 knots (50 -14 or so). Please don't try and sail with that much sail in more wind or rough water. Cats have maximum righting moment until they lift a hull and then lose it quickly. I would always urge you to keep the windward hull WELL into the water.)

As to why Chris White talks of needing 100 000 ft lbs of stability, it is probably down to waves. There was lots of tank testing done at the Wolfson facility. They found that a cat could not be capsized by waves (in the tank) if it was over a certain size. In the early 90s around 35ft, maybe 40ft, was the size that most designers thought had enough rotational inertia (to counter breaking waves) and stability (to counter rig loads) for a cruising cat. The rig you can design for a cat's stability but dangerous breaking waves have a certain amount of energy in them and the design must have enough stability to cater for this.

Maybe its the centre of gravity but here we really strike out. The galley down and semi custom build keep the CG very low for a cat - much lower than an equivalent French condo cat. This low CG should be a real asset for keeping right way up.

Even the length of bridgedeck has me shaking my head. The huge amount of net up front would be better than just about any other bridgedeck cat in allowing wind underneath to escape. Leopard's really clean lines have me baffled. I have seen a Manta 40 with a stainless tower of power that must have weighed 100-200 kilos up high - no similar thing on Leopard. That CG must be amongst the lowest of any equivalent cat.

Then there is the boat overall. She looks very well fitted out and sits on her lines. I think she looks really good. I can't see anything screaming out - "Look at this way out idea over here!" She seems very seaworthy.

I really want to know what caused the capsizes. If we write off the design we have to know why. The reason is that a reefed Atlantic (and both boats were reefed) should be able to handle more wind than almost ALL cats out there. Most cats here in Oz are between 30-45 ft and we don't flip them often, yet here we have two examples of boats, much safer than almost anything we have sailing here, inverting. If the design had obvious flaws I would be very interested. I have designed and built two cats of my own design and two other multis from other very experienced designers, this is what I love doing. I can't see the problem in this particular design.

In fact this design seems rather clever to me. I started this long piece with a note on the Twiggy, remember that there are two (or more) types of stability, sideways and fore and aft. You really want to have more stability fore and aft than sideways. You can ease a sheet to get you back on your feet if you have too little sideways stability but if you nose dive easing sheet does nothing - it is all up to the boat. So the Atlantic is slightly narrower to ensure you don't have heaps of sail up on a reach and then pitchpole when you bear away. I really like the Atlantic design (although I would have a normal style cockpit and cabin.)

A big cat design by my boat's designer has had two of his boats flip and no-one really seemed to care. We can look at them and say - "Of course - it's a big rig on a light boat - Duh". Big Wave rider is a fab record breaking cat.

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With the above example, the Twiggy, and many other examples of capsizing we could easily see the potential problem but here all I see is a cat that is absolutely first class and better designed and built than most out there - yet we don't have one sixth of all cruising cats inverting - even performance cruisers like Pescotts and Graingers. That is why I think it has to be something more interesting. Keep looking into it and do the maths. The answer is out there somewhere. When we get it then we can all learn even more about our boats.

cheers

Phil

[Polux]

Originally Posted by catsketcher

...
... So how could she flip?

Is it stability? Boatguy talks of his boat being proportionally wider but we have to be careful here. The square cube rule means that a cat twice as long will be 16 times more stable (if all other proportions stay the same). Stability goes up by the power of four but rig force by the cube. Going bigger is undoubtedly safer, so you can make a big cat a little bit narrower proportionally than a small one and still be way safer. I don't think it is stability, the Atlantics have huge stability.

... You really want to have more stability fore and aft than sideways. You can ease a sheet to get you back on your feet if you have too little sideways stability but if you nose dive easing sheet does nothing - it is all up to the boat. So the Atlantic is slightly narrower to ensure you don't have heaps of sail up on a reach and then pitchpole when you bear away. I really like the Atlantic design (although I would have a normal style cockpit and cabin.)
....

That's because a bigger boat has more stability that on really big monohulls some opt for a smaller AVS (even if always bigger than 100º). It is considered than the risk to be rolled by a wave is much, much less.

But there is a big diference regarding a cat: A monohull cannot be capsized by wind alone while a cat can.

When on a bigger cat you don't maintain the proportionality in what regards beam, and make a proportionally less stable boat (even if with a much superior overall stability), that makes sense in what regards being capsized by waves, but in what regards being capsized by wind it only makes sense if the bigger cat as a proportionally smaller rig (SA/D) and that is not normally the case in very sportive performance cats.

[44'cruisingcat]

Originally Posted by Dockhead

Guys, lay off Polux. I disagree with him frequently myself, but he's extremely knowledgeable and is a great contributor here.

When it comes to multihulls, I disagree.

Originally Posted by Dockhead

This is getting over the line to personal attacks, which are not allowed on here.

Unless they're made against me, apparently.

Originally Posted by Dockhead

In any case, you are mistaken to get irritated in this case, as it is well known and obvious that Polux likes boats in general and has nothing against cats per se. I call myself a "boat slut", since I love all boats, monos, cats, even power boats, and I think Polux is the same.

Again, I disagree. Almost every post he makes in reference to multihulls is negative. And those that aren't entirely negative tend to fall into "the faint praise which damns" category.

Originally Posted by Dockhead

Polux's point here is an absolutely fair one -- that 20% of all Atlantic 57's experiencing sudden capsize is really a damning statistic. It absolutely is a damning statistic. It clearly shows that the stability characteristics of the vessel and the rig don't suit each other, if security against sudden capsize is important to you (might not be in case of a hot racing boat).
Bavaria Yachtbau have built, what, maybe 100,000 yachts? Imagine if 20,000 of them had experienced keels falling off. That is what the case of Atlantic 57's looks like, statistically. Doesn't mean it's a bad boat (on the contrary, it's gorgeous ). Just means there's a design problem, probably one which could be fixed.

And again I disagree - you're talking about a very small sample. If a one off capsized or sank, a 100% failure rate, does that mean the design was wrong?

Or for example, the keel falling off an Oyster yacht - far fewer Oysters have been built than Beneteaus, (without knowing actual numbers) it's possible that this one instance represents a higher proportion than the number of keels which have fallen off Beneteaus - so does that prove Oysters have inferior construction to Beneteaus? Or that they have some problem Beneteaus don't have?

Or how about this - no cruising catamaran bigger than 60' has ever capsized, but hundreds of large 60'+ monohulls have sunk. (Including the large Oyster recently) Does this prove that large monohulls are less seaworthy or safe than large catamarans?

[robert sailor]

Originally Posted by 44'cruisingcat

When it comes to multihulls, I disagree.





Unless they're made against me, apparently.



Again, I disagree. Almost every post he makes in reference to multihulls is negative. And those that aren't entirely negative tend to fall into "the faint praise which damns" category.



And again I disagree - you're talking about a very small sample. If a one off capsized or sank, a 100% failure rate, does that mean the design was wrong?

Or for example, the keel falling off an Oyster yacht - far fewer Oysters have been built than Beneteaus, (without knowing actual numbers) it's possible that this one instance represents a higher proportion than the number of keels which have fallen off Beneteaus - so does that prove Oysters have inferior construction to Beneteaus? Or that they have some problem Beneteaus don't have?

Or how about this - no cruising catamaran bigger than 60' has ever capsized, but hundreds of large 60'+ monohulls have sunk. (Including the large Oyster recently) Does this prove that large monohulls are less seaworthy or safe than large catamarans?

Actually the way this newer Oyster was built was in fact a crappy build and it is inferior to a Beneteau.

[neilpride]

And I remember Oyster got a hard beat in the forums.... Actually well deserved.....

[44'cruisingcat]

Originally Posted by robert sailor

Actually the way this newer Oyster was built was in fact a crappy build and it is inferior to a Beneteau.

And so you'd use that to damn all Oysters?

[Factor]

[QUOTE=Dockhead;2270607]

Guys, lay off Polux. I disagree with him frequently myself, but he's extremely knowledgeable .

No he isn't, he has (statistically speaking) NO experience in actually sailing multis, and yet he feels entitled to stridently push a point.

In any case, you are mistaken to get irritated in this case, as it is well known and obvious that Polux likes boats in general and has nothing against cats per se. I call myself a "boat slut", since I love all boats, monos, cats, even power boats, and I think Polux is the same.

I respectfully disagree, the statistics of his negativity are, to use your words "damning"

[Polux]

Originally Posted by catsketcher

....
A big cat design by my boat's designer has had two of his boats flip and no-one really seemed to care. We can look at them and say - "Of course - it's a big rig on a light boat - Duh". Big Wave rider is a fab record breaking cat.

No Cookies | The Mercury
...

You mean this one is a Chamberlain 14?


Than we have more two to join to that list of big performance cruising cats that have capsized. I new about this one didn't know about two. Again, big performance cruising cat, very few boats made, two capsized?

I read about that capsize on the river. They said it was a gust from the mountains.
The Chamberlain 14 is a fast performance cruising cat not a race boat.

[JPA Cate]

I am glad we're now down to discussing design characteristics here. I had been of the opinion that the sample size was too small to conclude anything for sure, and am not scientist enough to understand if this is just bad luck for Chris White's designs, or the beginning of the solving of a mystery.

I would appreciate it very much if the guys here who are forceful with their opinions would take the chips off their shoulders, and "play nice". I find it quite dreary to read all the posturing. Toughen up, let the innuendos go by. Don't even post till you've finished feeling annoyed.

It is interesting to me that no one has suggested that the crew statements might be false in order to protect their reputations, and I am glad of that. When I read them, they sounded true to me, but sometimes people are very skeptical.

If we take them as true, then the skipper's not mentioning a wind shift with the occurrence may mean that it was not a waterspout, but some form of way stronger gust.

I hope we can get enough information to figure this one out.

Ann

[Factor]

Originally Posted by Polux

The Chamberlain 14 is a fast performance cruising cat not a race boat.

This boat holds the record for a single handed circumnavigation of Australia. I have sailed on it, have you. Hell have you even seen it. I know the bloke who built it, I know the designer, with those facts in place, respectfully disagree.

[44'cruisingcat]

Originally Posted by Factor

This boat holds the record for a single handed circumnavigation of Australia. I have sailed on it, have you. Hell have you even seen it. I know the bloke who built it, I know the designer, with those facts in place, respectfully disagree.

IIRC, it also won NZ-Aus single handed races? But not a race boat...

[44'cruisingcat]

Originally Posted by Polux

You mean this one is a Chamberlain 14?


Than we have more two to join to that list of big performance cruising cats that have capsized. I new about this one didn't know about two. Again, big performance cruising cat, very few boats made, two capsized?

I read about that capsize on the river. They said it was a gust from the mountains.
The Chamberlain 14 is a fast performance cruising cat not a race boat.

Don't get too excited.