Multihull Capsize Prevention <split>

Perhaps we can move posts 111 onward into a new thread titled "Multihull Capsize"

< thread split from http://www.boatdesign.net/forums/mu...llision-survivability-38047-8.html#post555597 >

 

I'm in agreement with James here. Capsizes on multihulls are sail handling errors. Best to invest in good sail control systems and get used to them. Reef early and don't get greedy with vmg in bad weather. Slow down to monohull speeds. Pay attention (no autopilot in bad weather) and be ready to adjust according to conditions.

The multihull isn't going to flip unless you flip it with a sail handling error.

 

Some great points James, but of course mistakes can happen so any thing that enhances the crew & passengers safety if a cat does flip would be a good thing, imagine watching people slide off to be lost when a simple coat of highly visible slip resistant coating & some lines etc could have saved them, kinda like seat belts. Jeff.

 

But there have been quite a few sailing catamarans capsized in rough seas?

One of the big dangers with a cat is being picked up under the bridge deck and surging with no control whatsoever. It's quite terrifying. My experiences sailing cats are that everything is going really well until suddenly it isn't at which point either it goes pear shaped or you get a 2nd chance and deploy the paraphernalia and/or put up the storm jib.

The cats that were blown over appear to have been hit unexpectedly by strong squalls or downbursts which mid ocean are not forecast. South Pacific convergences come to mind as classic unexpected sail shredders.

 

Actually, the correct number of catamarans capsized due to wave action is 0.

It is always a case of too much sail up for the conditions at hand. Ever seen a capsized power cat?

Performance sailing catamarans are serious machines. They need the same respect a drag racer, cbr 900 rr motorcycle, or an indy car gets and you have to be that good to sail them safely.

It's not such an issue on heavy, low powered production cats. Notice that every capsized cat you can come up with is a performance sailing cat (like the one I'm building).

One argument for the orange non skid is also less fairing to do. I may go that way myself, but i am trying to emphasize how much more important not capsizing in the first place is.

 

That's quite an extraordinary claim! It depends on the relative size of the waves and the craft. Waves can and have capsized catamarans.

But to get it in perspective it takes horrific sea conditions generally with wave heights close to the vessels length. No small craft can be invulnerable.

This is a one liner that would lead to a tome on naval architecture, and certainly a new thread, I don’t think it’s a very useful observation.

For example ask yourself how many under 40 foot power cats would be mid ocean in a storm?

There's nothing to suggest that sailing cats flipped in large seas were over-canvassed at all. Rather that they were simply picked up by one large breaking wave and were suddenly and violently inverted.

Wave response for catamarans in waves have been researched and well described. You can invert a sailing cat in a wave tank from wave action alone easily enough, while a power cat shows more energy under the GZ curve to AVS and resists the same wave. Power cats can be remarkably stubborn about succumbing to the sea But you cannot compare them as a valid observation, they are quite different craft.

In smaller craft there is a definite trade of survivability for performance oriented goals. Low bridge decks reduce COG but make the craft vulnerable to surging. Fine entry and low reserve fwd buoyancy don't allow waterplane area to shift fwd in wave encounter and dynamics force the bows down, then does the bridge deck save the day and give lift or act as a diving plane....
Even too little weight. It's actually the greater displacement that makes the power cat more seaworthy that it's sailing brethren.

And in an attempt to keep this a tiny bit on subject; that weight also makes the power cat suffer more damage in collision if it doesn't 'ride over'.

 

Well, find an example of one and post it then. If you can find a single example of a catamaran capsized by wave action, I'll stand corrected. For now, the tally is still 0.

I apologize. I don't know your background as a designer or mariner, but what the heck is "mid ocean" and what does that have to do with wave period, height or how steep a wave is? Some of the worst waves happen when the wind is from one direction, the current is from an opposing direction and there is some kind of interference from converging currents... such as in the Gulf Stream, which is not "mid ocean."

Sure... I'll ask myself how many power cats would be "mid-ocean" and I'd come up with an answer: Every single Leopard powercat that is in charter in the virgin islands was delivered on its own bottom from South Africa, crossing the Atlantic Ocean. I think it's safe to say *every* one of those was "mid-ocean" at one point.

Again... show me an example of a capsized powercat and I'll gladly stand corrected.

I'm sorry, but your post shows very little experience with piloting catamarans. Again, I don't know your personal experience, but you are speaking in conjecture and guesswork. Nothing you have posted is a fact, it's just speculation. Nothing in your post is based on examples of actual capsized catamarans. You should go through them all first, before assuming you know what caused the capsizes. This stuff is very dear to my heart, since I am building one of the "risky" ones right now.

Fact is, there are no capsized power cats. Fact also is, there are very few (if any) capsized production cats (heavy and slow, with small rigs). Every single capsized cat has been a performance cruising cat (or racing cat) with someone making a big mistake with the rig based on conditions they were in.

Show me an example of one of these cats that was "picked up by one large wave and inverted" and I'll believe it.

Read Up: Here is some more information, from one of the world's best catamaran designers that explains it all - http://www.sailingcatamarans.com/stability3.htm

A quote from the link above to Richard Woods' site: "Perhaps the most obvious statistic is that, to my knowledge, NO cruising catamaran has EVER capsized when under bare poles. To capsize with sails up implies a fair degree of "operator error", whereas its only when under bare poles that the boat MUST look after the crew."

PS: Yes, we are talking about 10-25 meter cats here of course, not beach cats.

 

power cat capsize at 1:28.

http://youtu.be/iGnPGxaWp4g

 

James you sort of lost me on this one, not sure what your saying so I'll ramble. Adding weight to a light weight boat isn't a good idea. I think flotation is necessary but needn't weigh much more than the air it contains. I like putting a layer of kevlar inside bows to reduce puncture risks but adding weight in the nose that needs to lift starts a downward spiral. The foam nose ideas banted around aren't a bad idea at all though. Bulkheads are definitely a good thing to put in a structure, my Nicol was designed with several easily sealed compartments. The bow shapes also tend to sled over things rather than impact which I like. The Tsunami debris is showing up but then we always have had lots of drift up here, slowing down at night is a bummer but avoiding a crash is better than surviving one. Jim Brown's book "The Case for the Cruising Trimaran" is closer to my style and has neat sections on disaster preparedness as well as capsize recovery which seems a fun thing to combine with those bulkheads. We also carry immersion suits but I've been in enough scrapes to know not to count on anyone coming to the rescue, the water is a bit cold up here. I remember hearing that Benny Goodman was cajoled onto that fateful flight by an officer saying "Come on Goodman, you want to live forever?" Flying low they then apparently were bombed by their own planes jettisoning their ordinance after a failed attack because their allies didn't know their flight plan.....

 

Re read your post James and if you were talking about bobbing around in a liferaft I agree that your boat anyside up is a better solution. It is important that flotation can support this though....Bows too take different treatment, a slicing bow is a different animal from a lifting one, as usual a cookie cutter approach won't work preparing a vessel. They are all too different.

 

Gooday 'cav' - aka Nth-West sloping bow sailor person - great for you to bother answering me. Thanks !!!

I grew up in West Van & sailed in the 50's - raced with the mob at VYC, @ Point Grey (lived right next door) in all classes from 'Snipe's' to 'Star's'. Did a lot of singlehanded sailing in a 'Raven' - which I still look back on fondly. Used to go out for up to a week way back then.

Now live in Northern Australia, been a yacht builder/repairer/sailor all my life since. Warm weather out here & swimming-pool like ocean except for the bities. Big problem in North OZ & SE Asia is the masive number of containers floating in the sea & the humungus number of container ships. Can't stop cantainer ships (get out of bloody way & do it very quickly) (Radar & AIS is good) - but running into containers - from 1/2 floating to mostly submerged - is a nightmare of disasterous proportions - for sure.

In my FRP business I 're-bowed' a fast tri heading from Cairns (where I still live) to Darwin then on to South Africa. He wanted some ultimate protection - so we stuck some very light weight foam on the bow - faired it in - - put some glass & epoxy over the foam - - checked for line & fairness - - then when happy - we layed-up several layers of carbon & kevlar - rotating the laminates several times & finished up with 4 layers of kevlar. The total of the laminate weighted only 1/5 of the bouyance that we had added. We then faired the whole 'new bow' structure & painted it. Finished product gave him a net result of 750 mm longer main hull on the waterline, more bouyancy & a bullet proof bow. Laminate was heat cured & was 12 layers of 450g/ sq mtr - double overlaped at the bow - going back - staggered - up to 300mm. When finished not one person could see where the bow addition jioned the hull nor if there had ever been an addition. Afterall I did learn my FRP trade at Thermolite Plastic Products in Burnaby back in the mid to late 50's - great trade training. Trouble with fast multihulls mostly with plumbish bows (these days) is that they travel so fast & a night you can't see anything just in front of the bows - hell - you can't even see them in the daytime, when there just 2" above the waves. I've learned the hard way (read as very hard way) to slow down at night. We have a saying about - the 'don't-go's' - don't go east before 0700 - - don't go west after 1700 / but that's here in the tropics & especially when near the barrier reef. At that time the water is just an opque piece of black slate. I've a 'closed-circuit' polorized camera 20' up the mast wired to a 14" screen at the helm - for seeing 'into' the water - when in dangerous areas. Is that not every where in the ocean - dangerous when sailing, though ???

You did get all the 'drifts' I was meaning. I was not nor am trying to teach you how to suck eggs however thought it would be good to expand on your comments so that others might learn - to think about the problem - prepare for the 'bump' & take steps to not risk their lives. Haven't seen a 'repair servo' out there - mid ocean - well not yet anyway. Thanks for your valuable & knowledgable comments. Ciao - til next time, james

 

You'd like it here now James, more of the drift is heading into what used to be called the Queen Charlottes but are now the Haida Gwai ( think). Hard to tell what will show up when...
Been learning from your experience too, good to know what people have done and what has worked. I've had the camera idea too, we really eliminate most of the "accessories" though along with the power requirements. If we need more than 2 batteries something is getting thrown over....started on this thread thinking of field replaceable bows for racers, cruisers tend to try to preserve them

 

Probly doesn't count but a Cat flipped motoring across Wide Bay Bar a few years back with no sails up (Wide Bay Bar is a notorious bar on Australia's east coast)

 

CAV said:-
I remember hearing that Benny Goodman was cajoled onto that fateful flight by an officer saying "Come on Goodman, you want to live forever?" Flying low they then apparently were bombed by their own planes jettisoning their ordinance after a failed attack because their allies didn't know their flight plan.....

Cav, I think you got that story confused with Glen Miller.
That story too is a myth. The actual bomb disposal area was in the Lower North Sea---but Miller was lost in the English Channel. The official inquiry said the plane was lost in the fog and ran out of fuel.
I know this because I was In the RAF at that time.

 

That's not a real power catamaran. It doesn't count. That is a normal, narrow beam skiff where they basically cut out the center to call it a catamaran for marketing purposes. It's a bay boat or lake boat.

Ocean going power catamarans look like this: