Large Catamaran Flips In Sydney

[seaskip]

Actually I'm not sure you could fly a hull on a Seawind 1160, ( don't want to thanks) but I'd better be thinking about it, just in case. Anyone had that experience?

[44'cruisingcat]

Originally Posted by SVNeko

That is one damn buoyant cat.

Yes they are. Bob designs huge reserves of buoyancy into his boats. Our boat has well over 50 sealed compartments. And even if every one of them was flooded, it would still float.

[Glenn C]

Originally Posted by catsketcher

Good points all - a question of definitions - most production cats are slower than performance (custom often daggerboard) cats. And more expensive than a similar length mono. I get that. I tend to think "What mono would suit me?" I think Sayer, drop keel light Adams etc - an equivalent mono for me to live on.

If anyone is still reading this thread I thought I may conjecture about the cause. I am guessing but there is a physical reality that could have caused this capsize - it is called the death zone.

It is probably easiest to fly a hull when beam reaching in strong winds but this is the most dangerous point of sail to do this. It is a question of getting to safety.

In strong winds you can get a boat back on its feet by heading up (if going to hard to windward) or bearing away (when on a broad reach). BUT there is a nasty zone around a beam reach where either is applicable. Whereas if I fly a hull when going to windward a small helm correction to windward and some eased sheet will have me back down quickly (the safest way to fly - you end up slowing down and end up with luffing main) bearing away from a broad reach with some sheet eased, will have me with full sail and screaming along (okay - not too bad everyone still on board?"). Then there is the death zone.

On a beam reach flying the hull is much more dangerous. For one there is no obvious path to safety - do you head up or down? On a beam reach both are equal. Then you have the eased sheet and high drag mode which is when things get really ugly.

Say we are on a beam reach flying a hull and then get hit by a gust. Whereas going to windward a quick tug on the wheel will have me up say 7 degrees and splashing back down, the beam reach needs me to steer up or down 40-50 degrees for safety - a long way, maybe too long to get to 40 degrees true or 135 true before bad things happen.

As I already am flying a hull I reduce stability with every extra degree of heel. I have only one rudder in the water and if I try to bear away without easing sheet it may stall, the nose may dig in and reduce the boat's turning ability. I could shove the nose under, which is really bad. Even with the mainsheet flogging there may be enough drag in the flogging sail to keep me heeling and reducing stability if the boat doesn't turn - dump the genoa! I hope there are no overides and that the crew can do what the Kiwis did in San Fran and stay at their posts - when the boat is looking like inverting. If we are high enough by this stage the flogging of both sails could be enough to keep us going. This is with expert crew.

To be safe you should be able to steer the boat back down - on a broad reach bear away. Upwind head up. Stay away from the beam reach hull fly. You have too far to get back to safety. If we get hit by a gust on a beam reach, when hull flying, and the crew have the sheets in clutches, self tailers or get a tangle we are in a bad way indeed. Do you have reliable crew at each winch, with hands cupped around the barrel, ready to ease at all times?

I used to sail a 43 ft cat that flew a hull regularly but it was always upwind. When on mainsheet I would stare at the helmsman and have the sheet in my hand, always ready to ease. Lots of well tended tail ready to drop at any moment.

Of course there will be lots of people who sail big performance racing cats like Carbon Copy, Cyanophobe and the Raiders that will fly a hull any time they can. That is fine. These racers are well set up for hull flying and they sometimes shove them over and that is accepted. My thoughts are aimed at the performance cruiser type cat which is larger.

To learn about the death zone I would urge all performance cat owners to get themselves on an old Nacra or Mosquito or Maricat and find out about it on small scale. It is real and should be avoided, especially in gusty winds, or if any sheets are cleated. You will learn some real reflex actions to help keep you safe. In the meantime - keep the hulls in the water.

If someone told me I had to fly the hull on Kankama, I could do it. I would have my brother on the main and another friend who has done tens of thousands of miles on the genoa. Then we would go out in a smooth southerly or soueaster and wind the boat up on a close reach at speed on the lake. Then if she lifted I would have great steering and could get her back down by a quick tug to windward. Could break something and cost me lots of money, so let's not.

cheers

Phil

Thanks, very clear discussion of the 'death zone'. it will be interesting if we can actually get some information regarding this event. So far we have nothing but speculation.

As for the speed thing, I have passed and been passed by bigger and smaller boats either racing or cruising due to all sorts of factors, not the least being the competence of the folks on board

[catsketcher]

Leopard rig falling down - interesting if a little old rig design article by engineer Chris Mitchell. In it he says about cruising cat rigs vs racing cat rigs

Not only this, but it takes considerably higher windstrength to fly a hull and that it would be outrageously dangerous to fly a hull in such a vessel at those windspeeds. So, this raises a number of interesting issues not the least of which is the refusal of owners to spend so much money on an enormous rig and the risk of capsize. We understand that in France it is common for rigs to be designed to withstand 60% of the righting moment. Given a factor of safety of 2.75x it would follow that if one were to fly a hull this is exceeding the working load (effectivley 166% of the working load). It can be shown this means that yacht flys a hull with only a small factor of safety of 1.0x at hull fly. Thus the rig should be close to falling down, but not quite… Hmm, anyway this is what we had heard. This is something of a compromise position which may work best for a catamaran which is relatively light in respect of cruising catamarans.

To read all of the article

rig design hints - AES

cheers

Phil

[daletournier]

Originally Posted by danielamartindm

Really bizarre. I don't know how common it is in the industry, but I've been told that the rig on my Leopard 39 was designed to fail before wind alone would flip it. Waves, of course, are another thing.

I had a very experienced monohull sailor repeat this twice to me recently he said" all modern cats are designed that way to counter their bad image of flipping" ......its crazy how people come up with things and then rumour becomes truth.

Does anyone really believe the big manufacturers are designing the entire rig to be a fuse? Expensive fuse! Intelligence isnt a given.

[44'cruisingcat]

It's pretty easy to work out. If your shrouds are 12 mm wire, their breaking strain is a bit over 10 tonnes. More if it's dyform.

So if the boat doesn't weigh 20+ tonnes, the shrouds can lift a hull.

I'd think any boat that weighs more than 20 tonnes would have bigger than 12mm shrouds.

[44'cruisingcat]

Cruising sailors aim to never fly a hull. It's one of the many ways cruising differs from racing. Racers do everything they can to go faster. Including carrying far too much sail for the conditions.

I recently spoke to someone who had crewed on one of Shawn Arbers boats in a Brisbane to Gladstone race.

Running in 30-35 knot wind they were flying the full main and a spinnaker. And frequently scaring themselves.

As a cruiser, in those conditions you'd have NO main, NO spinnaker, and maybe 2/3 of a headsail.

The difference in safety margins is huge.

So sometimes cats get sailed over in races. It doesn't really relate to cruising.

[Seaslug Caravan]

Originally Posted by 44'cruisingcat

So sometimes cats get sailed over in races. It doesn't really relate to cruising.

No. As you sail further from your beloved and "predictable" trade wind belt, you will encounter situations where one is caught cruising with too much sail up.

Whether trying to make port before an approaching front and getting caught a little short, or simply persevering with an unreefed main as the wind increases unexpectadly knowing that soon you will round the approaching Cape and be able to bare off and carry on safely with the sail as is, or simply getting flattened by a bullet as you seek shelter under the lee of a high headland , or a sudden down draft from a storm cell at night. Eventually you will be caught in a situation with to much sail up.
Many times of your own making through fatigue maybe, and sometimes out of your control.

Having a plan, and the equipment to dump sail quickly is a must. A lot can be learned from the racers in this regard.

SO PLAN FOR THE WORST.

[Glenn C]

......Suck inside of Mobile with the Memphis blues Again

like a lot of stuff Dylan is so insightful.....in this instance not so much, as he only had to go through it twice....


"An’ here I sit so patiently
Waiting to find out what price
You have to pay to get out of
Going through all these things twice
Oh, Mama, can this really be the end
To be stuck inside of Mobile
With the Memphis blues again "

[UpOnStands]

Originally Posted by Seaslug Caravan

SO PLAN FOR THE WORST.

Which would be sailing in a heavily negative buoyancy vessel with 5 or 6 sea cocks just waiting to sink you?

[PaulinOz]

Originally Posted by 44'cruisingcat

It's pretty easy to work out. If your shrouds are 12 mm wire, their breaking strain is a bit over 10 tonnes. More if it's dyform.

So if the boat doesn't weigh 20+ tonnes, the shrouds can lift a hull.

I'd think any boat that weighs more than 20 tonnes would have bigger than 12mm shrouds.

Yep, 21 tonnes, 16mm uppers and 12mm lowers.

[sv Grateful]

Originally Posted by Seaslug Caravan

No. As you sail further from your beloved and "predictable" trade wind belt, you will encounter situations where one is caught cruising with too much sail up.

Whether trying to make port before an approaching front and getting caught a little short, or simply persevering with an unreefed main as the wind increases unexpectadly knowing that soon you will round the approaching Cape and be able to bare off and carry on safely with the sail as is, or simply getting flattened by a bullet as you seek shelter under the lee of a high headland , or a sudden down draft from a storm cell at night. Eventually you will be caught in a situation with to much sail up.
Many times of your own making through fatigue maybe, and sometimes out of your control.

Having a plan, and the equipment to dump sail quickly is a must. A lot can be learned from the racers in this regard.

SO PLAN FOR THE WORST.

Here's an idea. Maybe the guy with no offshore multihull experience should go sail his Hunter around the Bay and stop lecturing the rest of us who have.

[catsketcher]

Gday Paul

There may be something in the story if you come to the question with an engineering bent.

We really shouldn't be using breaking strain in calculations, rather safe working load or SWL. Often the SWL is less than half the breaking strain of the material or object. Your 16mm wire has a breaking strain of 18559kg. Its SWL would be 9300kg maximum. To lift your windward hull the wire has to lift 1/2 of the weight of the boat = 11000 kg.

So your cat is getting close to what Chris Mitchell wrote about in his article. The caps can't handle the hull flying load. Now you have other stays that will help but as well as a SWL you should also figure in a safety factor in rig calculations, above the SWL.

So on the surface of it, it does look like the bigger and heavier cats could lose their rigs before they lift a hull. Especially when they get older and heavier. I really don't know what safety factor is used in rig design how low the SWL is for rigging wire. With wire being subject to corrosion and fatigue issues I would think SWL would be quite low compared to breaking load.

cheers

Phil

[44'cruisingcat]

Originally Posted by catsketcher

Gday Paul

There may be something in the story if you come to the question with an engineering bent.

We really shouldn't be using breaking strain in calculations, rather safe working load or SWL. Often the SWL is less than half the breaking strain of the material or object. Your 16mm wire has a breaking strain of 18559kg. Its SWL would be 9300kg maximum. To lift your windward hull the wire has to lift 1/2 of the weight of the boat = 11000 kg.

So your cat is getting close to what Chris Mitchell wrote about in his article. The caps can't handle the hull flying load. Now you have other stays that will help but as well as a SWL you should also figure in a safety factor in rig calculations, above the SWL.

So on the surface of it, it does look like the bigger and heavier cats could lose their rigs before they lift a hull. Especially when they get older and heavier. I really don't know what safety factor is used in rig design how low the SWL is for rigging wire. With wire being subject to corrosion and fatigue issues I would think SWL would be quite low compared to breaking load.

cheers

Phil

If you're talking about a "fuse"
You're talking about wire breaking, not safe working loads.

[catsketcher]

Yeah I get that 44, but we can say that the rig shown may not be designed to fly the hull because a properly engineered rig will have appropriate use of SWL and safety margins. There may be some cats with a lower safety margins that could blow off a rig. We would have to check the rig designs.