Multihull Capsize Prevention <split>

John that is a good response. It's worth noting that capsizes on multihulls are quite rare and usually operator error. Taking the right approach in a survival situation has proven to be the key. Larger multihulls are certainly safer than small and they are very safe and very difficult (not impossible) to capsize. The dynamics of catamarans and trimarans are different with catamarans more vulnerable to wind capsize and trimarans (particularly low float volume trimarans) more at risk of wave capsize.

What can be learned from this thread the lessons are reef early, know how to operate drogues and parachute anchors prior to them being needed and have appropriate equipment for your boat, slow the boat down in very rough weather and show good seamanship by not taking unnecessary risks with the weather and or seastate. On the design side the discussion on inverted access, having safe areas in the boat to shelter when inverted and access to a proper grab bag and safety equipment.

It's also worth considering that a capsize doesn't necessarily mean the total loss of the yacht and often multihulls can be recovered and righted.

Statistically sailors have proved to be one of the safest groups and suffer fewer fatalaties than even canoeists. I found the following articles interesting in a general sense as well.

http://sailing.about.com/od/navigationseamanship/a/Why-Sailors-Die-The-Most-Important-Safety-Lesson.htm

http://sailing.about.com/b/2011/07/10/land-is-the-sailors-greatest-danger.htm

 

Thanks John for your objective way to pointing out the differences between all types of boats.

Thanks Corley for your useful links so, we can all learn from them.

I hope this is helping Buzzman and others now in providing options.

 

Thanks Mike , for passing on Chris' good tips and warnings, digged into that as I wanted to know more . . . .

Here's the blog about Anna, and the report of her owner/skipper about The Loss of Anna, and a video of the rescue of the crew.

Anybody any idea why they didn't use the escape hatches, the crew member outside to get in for food, drinking water and shelter, and the trapped crew menber to get out . . . .

• the trapped crew member tried to break open the escape hatch with a hammer and a fire extinguisher.

• he escaped by finding his way through the underwater deck hatch of the head with the risk of being tangled up inside or by the rigging washing around under the boat.

If I may be so bold, here some additions to Chris White's report in case capsize prevention fails . . . . .

• Have the escape hatches operable from the inside and outside at all times when sailing.

• If want to make the search easier, paint the bottom fluorescent orange instead of dark blue and white.

57' is large in my book, and this story tells us it can be done with one squall if one is careless and/or overestimate the capabilities of the boat.

Thanks to Anna's owner/skipper , for being so open-hearted about his mistake so we can all learn from it . . . . :idea:

Bon Voyage..!!
Angel

 

Angelique,

That is one of the thing I like about the multihull society, is that want to pass on any lessons learnt, from their own mistakes.

 

From what I read in the owners account the escape hatch was not openable when the boat was constructed the hatch was glassed into position and a hammer supplied to break it open but when they tried the panel would not break.

I guess this is where the argument over performance cruiser comes to the fore. Owners want a fast boat but that means more sail area in turn that creates greater risk of capsize and more requirement for prudent and early reefing.

 

Thanks Corley,

So it turns out they didn't have an escape hatch at all, the team designer/builder/owner only provided a false sense of security here . . .

And if it had worked the breaking way a lot of shelter inside would have been spoilt by water washing in all the time, so a very dumb construction . .

If you have to spend a week or maybe longer on the capsized boat, shelter, safety, and supplies are all in the hulls, so you need the possibility to get in "inscape" when you're outside after the capsize, and of course you need a safe way out when trapped inside, also it would be nice to be able to close the hatches, as far as ventilation allows, and not spoil the shelter to much by water washing in all the time.

Don't know if any inverted ventilation was provided, if not, Anna's trapped crew member could have suffocate.

Anyway, these kind of "escape hatches" have proved here to be a big mistake . .

Openable escape hatches also provides much appreciated extra fresh air in the hulls while at a tropical anchorage . . . . . but don't forget to close them in time . . . . :idea:

About the last point, I've seen a yacht in Niewpoort on the hard after it sunk caused by a crew member who opened the head portlight to let the stink out . . . . . and the water in at the next tack, yes it was a mono . .

Story is at page 48 and 49 and here, both links for those who can read Dutch.

Cheers,
Angel

 

I suppose it is a catch 22 with an escape hatch as to the right hight. If it is right for entry it would be to high for exit from inside. As well as what is the inverted freeboard/ water line position, that would influence the position of a escape hatch. A lot of thought would have to go into the location.

I suppose this all fits into the survival aspect part of the thread. You have to take into account all parts rather than one aspect.

 

For completeness, in addition to the reports that Mike posted earlier, a Catana 44 "Bayette" was flipped by waves in the Med in 2004, with the loss of most hands. A number of accounts can be found online.

However I mildly disagree with posters saying that monohulls can be more seaworthy than multis.

It depends entirely on the expected range of operation of an individual design.
For a typical cruising sailboat around 40', a monohull could be capsized by a >14' breaking wave, and a catamaran by a >40' breaking wave. Design fiddles can change these values a bit, but not a lot.
Once the breakers are big enough to flip the multi, then the self-righting ability of a mono starts to look attractive.

Breaking waves over 40' do occasionally happen, but breaking waves over 14' are hundreds of times more common.
Every time any boat flips over there is a chance of serious injury and death for the crew, even if the boat is completely undamaged and self rights straight away.

Example: if you avoid hurricane season and winter in the high latitudes then the chance of fully developed >40' waves is basically zero.
So for a typical circumnavigation the most seaworthy possible vessel would almost certainly be a multihull.

Squall-induced capsize was also mentioned earlier and it is certainly something that all sailors should study, but it isn't a purely multihull problem. There are cases where solidly built mono's hit by un-expected microbursts have sunk within seconds because they were "fine-weather" sailing with deck hatches open.
Both eventualities can be avoided by a conservative sailor as long as they know the vulnerabilities of the boat they are sailing.

 

Listen and read

I grew up in multihulls and for a while almost everyone I knew had either capsized or been involved in something unhappy - Rose Noelle, Twiggy, St Therese, Pumpkin Eater. I was once fixing up my Kombi and the mechanic who kindly lent us tools was the son of a guy on the board of inquiry into Bandersnatch.

So a couple of things I got from talking to these guys

Twiggy - Twiggy capsized twice - both times in hard running conditions with the kite up. She was a very powerful boat sideways but had less fore and aft stability than sideways. Not a good trait for a boat that gets hard driven. So a multi should have more sideways stability than fore and aft so that your least stable orientation is on the wind or reaching. Then you can ease sheet to get back on your feet. In both of Twiggy's capsizes releasing the kite sheet did nothing. In fact this was the same for Sailmaker (another Twiggy) and Pumpkin Eater. A kite on a square run leaves you very little opportunity to save the boat if travelling fast. With a large increase in apparent wind blowing the kite is helpful but the fact is you can get rid of the main. John Hitch wrote of this decades ago and doesn't like mains or kites on a cruising boat. If pushing hard running deep you run the risk of not being able to depower the boat if you stuff the bows in.

Rose Noelle was a boat I helped do a small amount of work on. She was probably the best built and deigned tri I ever saw. She was lying a hull in waves which is not that sensible. That being said her skipper John Glennie had lots of experience crossing the Pacific on a Piver Lodestar. Lying ahull on a tri is problematic as the boats can roll quickly due their low roll moment of inertia. Cats are much harder to roll due to their greater roll moment of inertia. Still it is probably better not to lie ahull. John was tired and didn't want to lie ahull . He wanted to run off but none of the rest of the crew could steer. So he put out a parachute but it got tangled. He should have cut it free but he had just bought it (from my mother) and he didn't want to lose it. When they capsized the EPIRB (also bought from my mother) didn't bring help. (Don't buy safety gear from my mother)

Against this is the example of Ramtha- the owners wrote widely and were featured in the video on the Queens Birthday bomb storm. They like Richard left their boat under terrible conditions. It was found later and towed to Tonga (IIRC) They lost their parachute beforehand due to the float being too small and the steering system broke. The boat made it through without any help. The boat was a typical 38ft Simpson bridgedeck cat - a bit too little on the clearance for my tastes. It did show that a well designed cat can take an awful amount of punishment. The only damage inside were some cracks where the cupboards were glued rather than glued and glassed onto the hull side.

Rush was a 10 metre cat that has sailed the world from Oz. She capsized on her delivery trip to Sydney from Brisbane area. She split her gunwale and flooded a hull. She capsized and lost a crewman during the rescue when the helicopter line got caught around the hull and the line had to be cut. She was rebuilt and has taken a long while to go most of theway around the world. She had no interior furniture at the time and the large unsupported panels did not help. Also it seems as though she did not have the hull to deck join glassed as well as glued.

One interestig tale was that of Robin Chamberin and Terry Travers sailing to Antarctica in the late 1990s. They sailed down in Robins racer XS. As they sailed into Commonwealth bay they were told of strong winds. Casey station forecast the katabatic winds to stay up for overnight. The winds were pretty ferocious and the pair sailed XS downwind under bare poles with a drogue out the back. Robin is pretty adamant about not liking parachutes. He definitely prefers drogues like the one para anchors Australia make. This was put out for the duration of the storm. After a couple of days of a pretty terrible storm they found themselves about one third of the way back to Tasmania and so headed home afer being in sight of the continent most of the day before the wind hit.

As I own a boat Robin designed I asked him about parachutes. He does't like them because his designs have high bows and large rudders. He finds that this causes them to turn sideways when hit by a wave. I still got one but I also got the drogue he recommends.

In Jim Brown's book and the Multihulls magazines from 1976 is the tale of Meridian. In that the crew do not have an escape hatch and make a hole in the side of the boat with a winch handle. They made the hole too low at first and had to block it up and then put one up higher. I think this is the problem with most escape hatches. They often seem to be in the bridgedeck floor or hull side. That is fine for getting out but for staying with the boat it is less useful. The boat really needs a high and dry place for the crew to stay - out of the water. This will usually entail cutting a hole in the very bottom of the boat and having a deck underside to sleep on. This is easy on tris and certainly saved John Glennie and his crew on Rose Noelle and the Twiggy crew. Cats are much harder to get an inverted safe surface but my one is up the front on the underside of the floor of the sail hatch (about halfway up the hull).

So for mine I have a couple of axes tied onto the motor compartment and inside. When Lock Crowther was run down in Glucometer he tried to get inside with an axe but the thing flew off into the air after he whacked it - it was Kevlar. Kevlar boats need saws which is probably best for all boats.

Probably the best thing to do if you want to learn about other people and capsizing is to look for a few books - Jim Brown - The Case for the cruising trimaran, Phil Weld - Moxie, Cathy Hawkins - Return on the wake and John Glennie - Spirit of Rose No-elle. All tris but great for showing what to do to get through. Gavin Leseuers book "Windswept" goes through what happens when a cat disintegrates after hitting something in the water. After you av read lots of these articles you will have some strong ideas on what design factors you want in your own boat.

cheers


Phil

 

I'm sure it wasn't funny at the time but I find it amusing the big guy Lock belting into the hull with an axe and the thing flying off into the ether. If you were cutting into your hull with a saw you would I assume cut with an inwards angle so that the hull shell would drop back into position and stay there how do you hold it on once it's in position a spanish windlass and a length of line? screws if you have a battery screwdriver? The timesonline had a very good interview with the sole survivor of the Catana Richard Carrington it's a pretty torrid read. Theres a lot to learn from their experience.

 

Just re-read the Wolfson Unit multihull capsize report and the key findings haven't really got a lot of discussion on this thread.

1. The single biggest factor affecting capsize is the width between the hulls on the water - beam for a catamaran, hull to ama for a tri. Wider is better.

2. The other main factor is the AVS(angle of vanishing stability). The greater the range of positive stability angle, the less likely to capsize.

Righting moment, roll moment of inertia and displacement had a comparatively small effect or no effect on capsize.

This suggests to me that dynamic effects are smaller, and static effects larger than a lot of multihull commentators have thought.
Chris White (I don't think he's unusual, I just happen to have his book in front of me) talks at some length about roll inertia and area under the RM curve, implying that the main determining for capsize factor is: will the energy imparted by wave impact be larger than the total righting energy to AVS.
The Wolfson data implies in contrast that a multihull (without keels) will not roll until the face of a wave is big and steep enough that the boat would be hydrostatically lifted to near, or even past, it's static AVS. In this case no amount of RM or roll inertia will save you.


I should qualify that by pointing out it only applies to wave induced capsize. For wind induced (Captain induced?) capsize, then the traditional argument of RM and roll inertia still seems valid.
Increasing RM will increase the strength or duration of wind required, and increasing roll inertia will slow down the roll giving a better chance of corrective action.


How does this idea grab more experienced minds than mine?

 

Chris White actually has a whole series of articles on the capsize of Anna, not just the one, many of which would be worth reading in the context of this discussion. This should be the link to the index of them. The design of the escape hatch was a reaction to standard escape hatches leaking. If it had worked, it would have been a slick solution. The theory was sound; in practice it didn't work, and Chris won't be using it again.

 

Monohulls can be intrinsically much more seaworthy, they do suffer from parametrically coupled motion induced instability that a multihull doesn't (because the multihull almost instantly damps the roll out)

But importantly the level of skill required to reduce this risk is low, it's easily mastered and carried out by exhaused crew in severe weather and the boat can be ultimately left to it's own devices.
The vulnerability as you correctly point out is beam on to breakers an attitude to the waves that gives immediate and violent warning that you'd have to experience to appreciate.
Beam on vulnerability is a risk all types of vessel and a good rule of thumb is the beam relative to the breaking wave height from base to crest. But to lie ahull beam onto a breaking sea is untenable for the occupants in small craft so it doesn't feature highly as a major risk in my view. Unless you are racing and bound to take beam seas for your 'winning course 'seamanship' should prevail. It's accidental beam on exposure that is more of a concern, like a wave induced broach. With multihulls the level of seamanship needs to be higher for safe operation in extremes.

But there is again a lot more than can be considered here and you can produce a monohull that prove extremenly resistant to capsize and others which are death traps on steroids. Thats why a lot of the comparisons are flawed and don't consider what we can build rather than cherry picking data from quite different data sets.

That is intrinsic seaworthiness and survivablity. Self righting in any condition with the vessel sans rig but otherwise intact is a very reassuring feature for the scared skipper. And not only will your vessel be intact dry and habitable but you can usually effect self rescue.

Yet given the huge number of monuhull crusing sailboats the fatalities for these being rolled in heavy weather is virtually nill while multihulls inverted in heavy weather experience a high proportion of deaths. That's a concern I have. Simply that operators and designers don't appreciate how dangerous the upturned hull is in heavy weather.

If you confine the discussion necessarily to sensible Ocean cruising sailboats then I'd say downflooding is not a significant concern to properly operated multi or monohulls. I'd be interested in what you are counting here, to my knowledge it happens to extreme designs and tall ships but never to sensible offshore cruisers.

Yet it seems to be often cited as an argument.

I said earlier the monohull gives much better warning and takes less operator skill to keep it safe than a multihull does. I think that's inherent in seaworthiness too.

Also bad weather can develop in otherwise benign latitudes quite unexpectedly in many parts of the world, the idea that if you stay within 35 deg N to S that you are immune outside of the hurricane season is often cited but it's incorrect. It's just less likely, and the severe weather that does occur often wreaks a high toll on people who were least expecting it.

What I'm, saying here is if you go to sea and cruise blue water then expect and plan for storm force conditions. Don't talk the risk down and the imagined safety of your preferred design up.

Also it your comments about waves it's often the extreme wave you encounter that you don't expect and a typical fully developed sea state with a few underlying complexities commonly produces what some people call freak waves but are part of the normal wave statistics.

You can find wave height data looking like this commonly all over the world and they are actually normal events.

 

Mike, we seem to be drifting off topic and into the ever-fertile multi vs. mono debate. I'll try to be brief.

I wasn't "playing down the risk". I'm sure we both know that an objective measure of seaworthiness must be based on evaluating the probability of each risk and its severity. Compared to falling overboard, running aground, or being hit by the boom the risk of a massive (>30'), unexpected breaking wave on the beam is low, even in confused F10 conditions. It is always possible, and should be planned for by designers and sailors, but it is not the start and end of seaworthiness.

Sailors who believe that they will always be "safe" because their monohull will self right are just as dangerous as sailors who think that their multihull can't be capsized.

I think you exaggerate the difference here.
Capsize of "self-righting" boats has killed many sailors. This may be largely due to design and construction faults, but the same argument applies to multihulls.

Designers can make, and have made, multis that are safely habitable when inverted, and can self-rescue. The fact that these features are not common is not an intrinsic fault of the multihull configuration.


In 2008 in the Caribbean a charter cruising mono was sunk by downflooding after being hit by a squall. I imagine there have been others, but I haven't made a study of the topic.


I agree that any offshore boat should be prepared to survive Storm force conditions. Many multihulls have done so.

 

Good stuff Catsketcher Phil, informative, based on experience, unbiased, educational and not carrying a heavy steel axe to grind on your shoulder.