Atlantic 57 Catamaran Capsized

[Seaslug Caravan]

Originally Posted by catsketcher

Interestingly when I use Shuttleworth's formula and plug Kankama's (my 38ft cruising cat) rough numbers in I get an answer that says I will fly a hull in 24 knots. That doesn't seem right. I will have to go out with a tape measure and have a check. I have never flown a hull in her yet (and hope never to get the chance). Is anyone else interested in plugging their numbers into the equation and getting some more answers?

cheers

Phil

Phil, the number seems low as I get 20 .

It does say that: SF = windspeed in MPH that the boat has to reduce sail.

I notice another designer uses a constant of around 14 which gives the windspeed at which you get "lift off".

[seaskip]

Originally Posted by catsketcher

Here is an interesting article that does include large and heavy cats in its talk about rig design. A fair way down is a section on cruising cats. Some of the basics are

- heavy and large cats have huge righting moment - the loads on flying a hull are so large designers can just assume the sails will be doused or blown out before you lift a hull.
- mast designers are not sure if this is a good idea

Info – AES

It would be interesting to do more research on the number of capsizes and the SA/D ratio (Bruce number). I can pretty much guess that the higher the SA/D ratio the more likely a capsize. It is basic physics. The question for me, and maybe others is, where is a cut off, over which you are unsafe.

It is a bit trickier than it sounds. Condo cats have a much higher centre of gravity than other cats. On top of this the loads and motion of a higher CG and heavy cat are much higher. High sheet loads may cause injuries and cause owners to be less likely to do things like reef or trim sails properly.

Multi designers have always wrangled with power and weight. For most of my time in multis we were always getting rid of weight - excess weight made the boats less safe - structurally and with the problems like bridgedeck clearance. The more modern cats handle weight so much better and yet it is hard for me to change my tune because I like the feel of a nice lightish cat.

John Shuttleworth designs performance cats and tris. He has a few good artiles on this. One here

Considerations for Seaworthiness

Interestingly when I use Shuttleworth's formula and plug Kankama's (my 38ft cruising cat) rough numbers in I get an answer that says I will fly a hull in 24 knots. That doesn't seem right. I will have to go out with a tape measure and have a check. I have never flown a hull in her yet (and hope never to get the chance). Is anyone else interested in plugging their numbers into the equation and getting some more answers?

cheers

Phil

Sure am! Seems like a vital bit of info to me. Or is a seawind too much cruiser and not enough performance?😄 Going back a page or two, when people were using motorcycle analogies, I'd put an 1160 somewhere round my old Honda VFR. Capable of covering distances in comfort, slightly forgiving, but quick enough to keep others honest in the right hands. 😄 They called it a sport tourer I think.
Sorry, way off topic.

[seaskip]

Crumbs! Just looked at the formula. I can get approx D, SA and B, but CE is beyond me. Ideas?

[Polux]

Originally Posted by Catopia

A question: is it possible that the roaring sound the crew heard just before capsizing was from a rogue wave as opposed to a microburst?

It was not necessarily a micro burst and the sea was not agitated. There are more cases of big performance cats being capsized by a big and unexpected gust, a very strong one but nothing to do with the wind speed of a microburst.

I remember a TS 52 (performance cruising cat) that capsized in similar circumstances, I mean a big gust. The conditions were a a bit more musculated (f6) but nothing special for a 52ft cat.

"SEVEN French sailors cheated death on Wednesday August 1 2012 when their 16-metre catamaran capsized in a squall in the Sound of Sleat.

Force 6 winds were blowing when the Pampero’s 22-metre mast was hit by a freak gust and she flipped over between Knoydart and Isleornsay on Skye."
TS 52.8′ | Christophe Barreau

[Palarran]

Originally Posted by mikereed100

Where do I begin?

First, I would point out that the Atlantics all have a steering station in the forward cockpit with all sail controls immediately at hand. There would be no better place to be to respond quickly to a rapid change in the weather. This is in addition to the inside steering station.

Second, I would guess that most, if not all, cruising catamarans are sailed from inside the cabin with the autopilot doing the hard work. This is particularly true of short handed crew. To be sure, most people will move to the wheel when a squall approaches. Whether that wheel is in a pilot house, on the transom or behind a bulkhead is irrelevant. On our boat we don't rely on "feeling the first subtle signs of an approaching microburst in our nostrils and on our skin" to react to approaching squalls. By then it's too late. We are watching these things coming from miles away, visually and on radar, and the boat is made ready in advance.

Third, The higher you go in latitude, the more pilot houses you will see. People don't choose this arrangement because it is "DANGEROUS", but rather with the idea that a warm and comfortable crew is a more responsive and effective, to say nothing of happier, crew.

I can't say why 3 Atlantics have capsized, but I would speculate it is because they are on the performance end of the spectrum of cruising cats and tend to be sailed accordingly. I don't think it is due to any flaw in the design, and certainly not due to the forward cockpit/pilot house arrangement.

Mike,
It would be interesting to have a poll on where people sail from in cats. We are never without someone at the helm, or outside somewhere - ever. I use the autopilot a lot, but it's also within about 18" of my finger, right next to the wheel, and 3' away from the main sheet. When you sail do you actually go inside your cabin, shut the door, and hang out? Do others, I don't know.

FWIW, I also think comparing northern latitude pilot house monohulls to this situation is apples to oranges. Pilothouse mono's are typically built like bricks and can handle a few surprises, cats as we all know don't have the safety valve of heeling or broaching.

In the case of Leopard, it is guessing to say that being inside caused the delay that resulted in the capsize. But with Anna, after reading the captains first had account, I do believe that because of the weather and the location of the forward exterior helm, the crew decided to seek shelter inside. And that decision caused the disconnect to the weather and time loss necessary to respond to the wind gust.

There really isn't any comparison to the number of major problems Chris White catamarans have had to other manufactures as a percent of production. I think both of the foiling cats made so far have lost one or both of their masts. Three cats flipped. It's pretty high numbers. Most likely the owners realize they are signing up for increased odds when purchasing a cat like these, but it still seems pretty high. JMHO

[Cottontop]

Originally Posted by transmitterdan

It was interesting to read about Leopard's first Newport->Bermuda sail as told by the designer, Chris White:

https://chriswhitedesigns.com/leopar...ort-to-bermuda

It was especially interesting, in light of the apparent capsize of this boat, that Mr. White awoke in the night and "sensed" they needed to reef the main at 2AM.

Apologies if this link has already been posted.

Here's what Chris actually wrote. Not really so interesting:

"On the second night out I was sleeping happily in the windward aft cabin when my time for watch came up. It was clear from the water noise that we had gained some speed but I lay there for a few minutes trying to get fully awake then stumbled up to the pilothouse. The owner was hand steering from the inside station, plumes of spray occasionally shooting upward from the bows and boat speed ramping up into the low and mid teens. The wind had piped up and come forward a little. He had rolled up some of the staysail, and we had put a single reef in the main earlier, but it was now time to reduce further."

[Seaslug Caravan]

Chris White has details on his Web Page.

See... https://www.chriswhitedesigns.com/leopard-capsize

A couple of paragraphs below. Nice to know that the speculation is not limited to CF

.........

It is still early in our evaluation of what happened but my own opinion is that Leopard was overtaken by a tornadic waterspout. When sailing offshore, I have seen at least a hundred of these small tornadoes extending down from clouds. Mostly they are short lived and don’t extend to the surface, at least in a visible form. But some do. And these can vary in intensity from small “dust devil” winds to an EF2 tornado (135 mph wind) with diameters of a few feet to 100 yards. This is the best explanation that I can come up with that fits the facts as we currently know them; a) Leopard was close to an approaching cold front, b) There were no rain squalls in the area, c) the roar, and d) the suddenness of the huge wind increase and the lack of strong wind immediately post capsize.

A capsize could be caused by a micro burst from a thunderstorm or large squall. These can be violent and dangerous. But approaching squalls are normally visible, even at night and even when they don't have lightning. And in my experience even the worst ones have something of a “ramp up” phase where the first gusts may be strong but nowhere near enough to immediately capsize a large catamaran with deeply reefed sails. I’ve had my own share of surprises and scares with squalls but in every case I knew it was coming at least some large fraction of a minute before the big wind hit, and in most cases for 10 or 20 minutes. Unless you’re single handing and asleep there is always some time to react. It doesn’t take more than 3 seconds to step out of the A57 pilothouse and reach the mainsheet, I have timed it. And squalls don’t start and end in seconds.

[TeddyDiver]

Originally Posted by seaskip

Crumbs! Just looked at the formula. I can get approx D, SA and B, but CE is beyond me. Ideas?

CE center of effort ie the center point of sail area. Draw Your sails on paper and find the center of the area. For this regard measure the height of this point.

[SVNeko]

Originally Posted by Polux

There is a big difference between the 5x and the atlantic 57:




Those fixed keels (in addition to daggerboards) are a bad idea on fast light performance cats, they help to trip the cat when subjected to a big gust, much more than a smaller daggerboard, preventing the boat from sliding and inducing a rolling movement that can finish on a capsize.

So you think the mini keels contribute to a wind-induced capsize? Although I have some doubts about the effect in the real world, I understand the theory that boards up allows a cat to slide sideways on a wave impact. But with respect to being sailed over, even assuming every 5X has its boards up upon being hit with a big gust, I think the sideways movement and whatever relief that might allow from the force of the wind would be minimal.

[seaskip]

Originally Posted by TeddyDiver

CE center of effort ie the center point of sail area. Draw Your sails on paper and find the center of the area. For this regard measure the height of this point.

Thanks Teddy. It'll be rough but ah well.

[StuM]

Originally Posted by seaskip

Crumbs! Just looked at the formula. I can get approx D, SA and B, but CE is beyond me. Ideas?

Read the sections on S/Speed and KSI here:

Multihull Dynamics, Inc. - News Article

and the more detailed explanation at:
Multihull Dynamics, Inc. - News Article

That's a great site for data and comparisons on multihulls.

[catsketcher]

Thanks for the links people. It does seem as though the boat was being well sailed by someone with much more experience than me. They were doing 7 knots or less so obviously were being prudent. Maybe any other cat out there would have been flung over due to the special nature of a waterspout - they can lift cars and sheds so one would think that most multis would lift as well, sails or no sails.

As for the Stability number - I may have jumped the gun a bit. Derek Kelsall uses the same stability equation but instead of using a co-efficient of 9.48 he uses 15.8. That seems more like what I reckon. I have been sailing in 22 knots and not lifted a hull. The 30 something required by Kelsall's formula seems more in line with my experience. I don't go there with full sail. At least we know that very experienced designers can't really agree on how to work out when a hull will lift. Mere mortals have less hope.

http://www.kelsall.com/TechnicalArti...llFormulas.pdf

[seaskip]

Many thanks all. I'm off to study. ( maybe I shouldn't have had that glass of red with dinner)

[arsenelupiga]

put my physics hat on....


we know that Lagoon 420 capsized on mooring in cat 5 cyclone in Whitsundays, assuming around 150 kn winds and some waves caused it.

My cat is nearly same weight as A 56, and A56 has ~ 2x larger surface area assuming 50% longer and 50% wider.

1.5*1.5 = 2.25

Same for proportion of bridgedeck tunnel which may play role in capsizing.

So, rough assumption 2x less force required to flip A56 than L 420 due to structure only. Force proportional with square of wind speed.

sqrt(2) ~ 1.41, therefore A56 capsize danger with no sails is roughly 150/1.41 = 106 kn.

comments welcome

[Sos]

I don't think the forces involved with being hit by a tornadic waterspout would be anything like a normal squall. Sounds like bad luck rather than a fault with the boat or human error. If being at sea was predictable we wouldn't love it so much