Atlantic 57 Catamaran Capsized

[catsketcher]

Originally Posted by Polux

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.

Actually you don't have proportionality in ANY boat design. My first boat was a Manly Junior - it was 8ft long and 4ft wide. You don't make boats proportional. This is a really fundamental and basic point in yacht design.

Stability in cats goes up by the fourth power. Stability is displacement x 0.5 the beam. If you were to double the dimensions of a cat it is twice as long, twice as wide, twice as tall 2x2x2=8 times as heavy. So my 38ft cat is about 8 times heavier than my 19ft folding cat. And it has twice the beam so it is 8 x 2 = 16 times the stability.

Area goes up by the cube. If I double the mast height and double the boom length I get the sail area squared. I have doubled the height of the CE too so the overturning moment increases by the cube.

So if you double a cats size you get an increase in safety margin without doing anything at all because you gain stability faster than you get heeling force.

You can't use a simple formula like SA/D and expect it to be useful when comparing boats of different sizes. That is why Edmund Bruce invented the Bruce number - Sail area ^-2 / Displacement ^-3. This is all very basic design 101. Using a simple SA/D ratio is bad design practice.

There is a really good book that goes into the numbers used by multihull designers to understand their work. It was written years ago by an experienced designer who designed and built their own boats and was mentored by some of the best in the business. The section on design numbers, I am looking at it as I write, is between pages 45 and 56. It is a great resource.

The author is a bloke you may know - Chris White, designs these nice looking boats, is very big on seamanship. The book is "The case for the cruising multihull". Have a read, it's a great book.

Interestingly he talks about stability and vanishing angles on monos and breaking waves. Wolfson did testing on monos too, it was after the 79 Fastnet. They found that stability, per se, was NOT the only major factor in resistance to breaking waves. It was rotational inertia. The best boats at exhibiting a high rotational inertia - a typical cruising cat - the worst was an interior ballasted high (for monos) CG IOR style mono.

Also Polux - I included a link in a post before about a nice really well designed mono getting laid flat by a squall - that was wind alone. So monos do get laid flat - I call that capsized - that is what my racing sailors friends call it, by wind alone. You may be thinking turtled or inverted but capsized is mast in the water, knockdown style. Monos can do that fine on flat water - done it myself often with a kite going feral.

[transmitterdan]

Regarding the crew comments describing a "roaring" sound, I happened to be on a sailboat in a slip when a tornado passed directly through the pontoon we were on. My boat put the lower spreader and cap shroud against a nearby support beam and held there for about 30 seconds. No other damage but just ashore there were many trees knocked down. The sound is exactly as the Leopard crew describe it. It took several seconds (5-10) for the sound to build up to maximum "roar" just as they describe. If their cyclone passed directly in front or behind the yacht then it would appear to them as a huge wind from one direction (port or starboard) that built up rapidly over some seconds. The wind velocity on deck could have easily exceeded 100kn even for a small cyclone. At 15 meters above the water the velocity can be 25-50% more that at the surface. So their description is consistent with a tornadic event in my experience.

[Boatguy30]

Phil

Lots of good info. I was pushing to hard maybe it wasn't 18" could have been only 12-14. I was in pretty shallow water so o figured if I did go over it wouldn't be a full turtle! Was probably gusting to about 40. I was actually just inshore of Cape Canaveral on last Thanksgiving day. I reckoned I would be able to find an online tracker of the conditions for a place like that but could never find one.

I was crossing the gulf stream 2 months later in similar wind but at around 120 deg twa and up to maybe 2 meter seas. Did have a first reef in and got tipped a bit one time to fall over a bit from sitting in the cockpit anf a few things actually fell over from the galley dish rack.

That was sorta scary but we were soon on the Bahamas bank as the cold front began to overtake us. Took the main down at dinner time and the wind died much like the conditions Leopard had. Seas were less on the bank 2-3 feet so motion was OK.

Anyway long story short, several squalls blew thru doing 15 knots with just the 240 sq ft Genoa. Closed up the main cabin hatch for the first time (when not raining)as was taking a bit of water into the cockpit. Improved the drains when we got home.

I guess that maybe is the problem with these boats is you feel pretty safe until you're suddenly not. You reckon you go from 10 deg to 180 in an instant?

[Multihull]

the last sentence

+1

[poiu]

I questioned earlier if cats could flip whilst under bare poles and some people said they heard of it happening. I found a few examples on the web, with one especially good account of such an event in 2011 found under post 30 and 39: Cats flipping in gales at anchor or moored - Page 2. There are videos of this event around and pictures of considerable devastation, hurricane stylee.

The account is quoted below:

We are the owners of the Prout Snowgoose Elite catamaran "Sanyassa" which capsized in Vliho bay, Levkas on 20th. September 2011. First some background. We were 15 yrs. into a circumnavigation and had logged over 54,000 nm. During that time we have, as you would expect, experienced many storms both at sea and at anchor. I can categorically state that no level of seamanship could have prevented this capsizing. First point the forecast was for a maximum 9kts. although thunderstorms were expected. Second Ormos Vliho is recognised as one of the safest anchorages in Greece and is the place that many yachts go to when strong winds are forecast. WE were anchored, lying to a 25Kg Rocna anchor in 5M 100M east of the Sail Ionian Dock.


We were down below having our early evening G & T,s at around 6.30pm. The wind was light from the SE. It was quite cool. Suddenly I became aware that the wind generator was extremely noisy. I went immediately into the cockpit and started the engine and put it in gear, my wife switched on the instruments and noted a wind strength of 75kts. Our awning blew away and at that moment we were thrown onto our port hull to an angle of around 70 degrees, we started to come back upright when an increased in the intensity of the wind flipped us over. My wife who was just emerging from the saloon door was swept back down below and down the steps into the navigation area. (She suffered a cracked pelvis). I was flung across the cockpit and became submerged I managed to swim out and surfaced alongside the port hull. The waves which were about 2 ft. apart were washing over my head. Within less than a minute they had subsided and I was able to swim round to the stern and climb onto the upturned hull. My wife was trapped down below where she found an air pocket (she is a non-swimmer). It was less than 1 minute between being in our saloon having our sundowners and us capsizing.


One person was killed trying to fend off another yacht and was trapped between the hulls. 10 yachts recorded wind speeds of 100kts. at the height of the storm.


Ruari Bradley from Vliho Yacht Club arrived within 10 minutes, and heroically dived down and managed to pull my wife out. Pictures and videos have been posted on the Vliho Yacht club facebook page.


The question is would I still choose a Prout Snowgoose again if I was contemplating a circumnavigation. Yes I would.


I have been very disappointed with some of the postings on this and more especially other forums. I have only just found the time to read them. Perhaps the above will stop all the uninformed speculation regarding this unfortunate event.



First let my wife and myself thank all who have posted on this thread who have expressed there good wishes to us.

1) Did we use a bridle. No. Do I think it would have made any difference. No. We never have used one. We found that when all the monos were veering all over the place Sanyassa our Prout Snowgoose Elite would lie quietly head to wind just to her chain.

2) Yes the wind did suddenly veer. I would guess although you have to remember that it was less than 1 minute from being below drinking our G & Ts to me swimming alongside the upturned hull. There is no doubt that it was wave more than wind that initiated the capsize. My feeling is that a short steep wave heeled us to an angle drove us to leeward. The lee rail then dug in creating a turning moment. We started to recover frrom the first wave when a second wave capsized us. I would judge that the wind was just slightly ahead of the beam. More on this later.

3) I don't believe the awning was a factor, it blew away seconds before the capsize.

4) I don't know what a stackpack is so I can't comment but whatever it is I doubt that it would have made any difference one way or the other

So what do I think happened? Obviously I have given it a lot of thought. It was not a hurricane. They don't happen outside the tropics. In any case it was too localised. yachts at anchor 1 nm away in Tranquil Bay noticed nothing unusual. Yachts less than 1/2 nm away at the east side of the bay had a "mere" 60kts. My first thought was that it was a tornado and I thought when looked at the video that I could see a waterspout but now I don't believe it there. I am sure that it was in fact a microburst see:-http://en.wikipedia.org/wiki/Microburst. In a microburst there is a strong downdraught, this would have pushed large steep waves which would be travelling down wind at a considerable velocity thus producing the capsize as desribed above. At sea in strong winds and large waves Sanyassa would slide sideways down a wave where a monohull would trip over its keel.

Yes it was the fickle finger of fate. Were I staring out again i would still choose the same type of yacht and in the event that I was in the area of ormos Vliho and received a forecast for strong that's where I would head for.

[Polux]

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.

No but I can post a video of it. You can see that the boat has a quite comfortable cruising interior. What defines a race boat is its total commitment regarding racing and that implies the absence of any comfortable cruising accommodations. They are pretty much naked inside with the strict minimum to live aboard while racing.

I am surprised that you consider this performance cruiser (or cruiser-racer) a racer, with a tender on davits lots of "windows" and a comfortable cruiser interior with two heads!!!!. Even the seller says it is a performance cruiser:

https://www.youtube.com/watch?v=bC67iE5OYjs

[PhiSig1071]

As for the story of the Snowgoose that capsized at anchor, I wonder if having tramps instead of a solid foredeck would have made a difference? Most (all?) modern cats have tramps, so the underhull area is going to be much less for a similar sized cat. In order to get the same underhull area as a solid fordeck Snowgoose you'll end up with a much larger (and heavier, and more stable) boat. Also, aren't the Prouts relatively narrow, compared to more modern cats?

[poiu]

Here is quite a good video of a tornado/waterspout 90 deg knockdown to a Clipper yacht. Shows how quickly things go awry. The knockdown took just a few seconds.

https://m.youtube.com/watch?v=Z5vA4Q...=youtu.be&t=29

[Polux]

Originally Posted by catsketcher

Actually you don't have proportionality in ANY boat design. My first boat was a Manly Junior - it was 8ft long and 4ft wide. You don't make boats proportional. This is a really fundamental and basic point in yacht design.

Stability in cats goes up by the fourth power. Stability is displacement x 0.5 the beam. If you were to double the dimensions of a cat it is twice as long, twice as wide, twice as tall 2x2x2=8 times as heavy. So my 38ft cat is about 8 times heavier than my 19ft folding cat. And it has twice the beam so it is 8 x 2 = 16 times the stability.
.....

I don't really know what you call stability, but in what regards righting moment (that I think it is what you call stability)the factors are not only the displacement and beam but also the position of the CG, that can be different from cat to cat. Total stability is given by the surface under the RM curve on all heeling points till capsize. That corresponds to the total energy needed to capsize a cat.

When I was talking about proportionality I was talking about the Rm generated (on a smaller or bigger cat) and the sail area that RM is able to conter act with safety, on a bigger or smaller cat.

[Polux]

Originally Posted by Factor

This boat holds the record for a single handed circumnavigation of Australia. ...

I found strange that a performance cruiser cat could hold the record of single handed circumnavigation of Australia and after looking at the record, that is a bit under 39 days (that's a lot of time) I understood why. It seems that there is a lack of candidate for doing that record and even if in Australia there are some fast racers, there is not a solo racing culture neither really fast solo racers.

The only serious record from a true racing boat has already 11 years, on a multihull that today would be considered obsolete, old Geronimo, with a French crew that has made it in about 17 days and a half at more than the double of the average speed of that performance cruising cat.

I know that it was a crewed record but if that record was attempted today by a true racing multihull record breaker the solo mark would be very close if not better than that crewed record with 11 year. That's how much solo sailing has evolved in that time.

The Absolute crewed circumnavigation record in 2004 was 58d 09h 32m 45s, the actual solo circumnavigation record is less, 57d 13h 34m 06s and Covile is on the sea trying to beat that one and it has a considerable advantage. If nothing wrong happens we will be breaking that record.

[catsketcher]

I love learning as much as I can but sometimes the internet can get me cranky. My blood pressure meds will be needed if I don't have a break for a while.

cheers for now

Phil

[Dockhead]

Originally Posted by neilpride

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

Indeed. The point being that the single keel failure was not a freak event.

Sent from my D6633 using Cruisers Sailing Forum mobile app

[Polux]

Originally Posted by 44'cruisingcat

...

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?

That example with the Oyster has nothing to do with design but with built quality or a structural miscalculation. Regarding a cat it would have been if the connections between the two hulls had broken and the boat sunk due to that.

What we are looking here, and directly related with this accident, has nothing to do with structural strength or built quality but to know if fast performance cats have not gone too far away in what regards sail area versus RM to have an adequate safety margin as performance cruising sailboats. Is that particular design item we are looking at.

The numbers regarding capsized boats and built boats regarding the Atlantic 57 are well known, regarding the TS 52, at the time of the capsize 2 were built one capsized (don't know if more were built after). Regarding the Chamberlain 14, two capsized and how many were built?

[daletournier]

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.

Ive seen the boat a number of times, maybe a race boat but I'm fairly certain the guy cruised on it to,so was it also a cruising cat? Looked like a really fast cruising cat to me. Can't this particular boat be both? Or is ,it both depending on useage? You guys are hilarious!

Sent from my vivo Y35 using Cruisers Sailing Forum mobile app

[smj]

Originally Posted by Polux

That example with the Oyster has nothing to do with design but with built quality or a structural miscalculation. Regarding a cat it would have been if the connections between the two hulls had broken and the boat sunk due to that.



What we are looking here, and directly related with this accident, has nothing to do with structural strength or built quality but to know if fast performance cats have not gone too far away in what regards sail area versus RM to have an adequate safety margin as performance cruising sailboats. Is that particular design item we are looking at.



The numbers regarding capsized boats and built boats regarding the Atlantic 57 are well known, regarding the TS 52, at the time of the capsize 2 were built one capsized (don't know if more were built after). Regarding the Chamberlain 14, two capsized and how many were built?

I believe a structural miscalculation would be considered a design failure.


Sent from my iPhone using Cruisers Sailing Forum