Multihull Capsize Prevention <split>

I've wondered exactly the same thing.

I'm not aware of any wind tunnel testing on the subject, which is what we really need.

 

Great picture. Some loads here that wouldn't usually be considered !

It would be best for the recovery vessel to tow from windward of the stricken vessel. It would be much easier to recover a Trimaran of this size too. Experienced sailors as well and a big list of mistakes they compiled after the caspsize.

 

I agree, everyone on board needs to know how the boat will sit when it's upside-down, not just the designer. Knowing that it will "float" is not enough.

Where is there going to be dry shelter on your boat when it's flipped?
How will you get in and out -is the escape hatch also going to be high and dry?
What supplies will you be able to reach?
How will it sit relative to the wind and wave direction?

 

On the one hand i would agree. On the other i would disagree. Only because no 2 boats behave the same. There may be "generalities" but beyond that, VCG, LCG, windage, roll/pitch moments of inertia to name a few are all variables and can contribute in a minor way or a significant way. Too much to really compare boat A with boat B.

Precisely.

Thus we must examine the hazard, not the boat per se. Since the hazard shall lead to a different outcome for each boat, beit mono or cat or tri. Once the hazard is identified, that forms the basis for the risk assessment, and mitigation as such.

You cite the "foil" shape of bridge decks as one. Clearly this is only applicable to multihulls. I think I may have a report/paper on this somewhere, I'll have a rummage around.

 

Some thing to remember with the capsize of eDoc is that it was in 30 feet of water, mast hight is 50 feet, so it was not totally inverted.

Gavin got upto 14 points of mistakes he made in the multihull world article he wrote up about it it may be found on the www.multihullworld.co.au website under pdf files I have not been able to open the web site today to check if it is there.

 

An F boat was blown backwards off a wavetop with loss of life do to a wide web/mesh net while racing. Recently on another forum a Prout was shown capsized in harbor whem a cyclone came through. Sometime ago I sketched out a under water "inverted parasail" weighted with chain for harbor hurricane conditions to help keep a light boat from flying. A heavy jib could be used in a emergency but these methods wouldn't work in a big sea- you couldn't side slip....For Angelique- a low LAR will side slip, just not as fast!

 

in reality the shorter floats give you more warning your getting into trouble so help prevent a diagonal capsize.

The beauty of the B24 and F-boats is the small floats submerge but don't slow the boat down much, its almost like sailing a keelboat (main hull wont come out), almost impossible to tip over and will actually broach like a keelboat.

If you run a GZ curve on a tri with high dihedral and light rig (like the B24) its crazy how far it can go before losing stability, over 80 degrees.

Bigger/ longer floats make a tri sail like a cat. Feels all good so you keep pushing, then when it digs a bow in your in real trouble...

 

We have an 100% agreement here, I said...

‘‘don't have LAR keels on a cat if you want to be able to make full use this feature in a situation where all hell breaks loose’’

Meaning LAR keels don't side slip as fast as no keels and boards up.

Which makes LAR keels closer to the edge of capsizing compared to correctly operated* daggers.

* Alas... there lies the weak point of daggers as most capsizes are caused by operator errors.

Cheers,
Angel

 

Thanks for your insight into float length Samnz.

I just reread the article on the aDoc capsize and the water depth was not 30 feet but 4 metres

 

Oh - Is that why 'Umi' did - trip-over - how interesting - eh ??? Ciao, james

 

Well Yumi Maru had a tendency to broach and in her capsize she broached then capsized over her leeward float while running a masthead kite. Phil Smith rebuilt the boat with larger floats to reduce the tendency apparently it worked.

 

Great post Samnz..!!

Think you nailed a problem that Mike mentioned earlier. A lot of multi sailors who get in trouble don't know the edge of a boat that don't gives clear warnings . . . . People with big money buy big boats on which they don't have experinece and also often have a lack of knowledge of, but of course are in denial of both. And they are right all the time as long as the weather is nice. So how should these people learn where the edge is if the boat feels safe till they go over . . ? ? Those boats are sold with talk about sailing machines that don't heel etc, but what licence do you need for such a machine that has hidden dangers for the ignorant . . . ? ? ?

But Hey, guess that those who need the massage about this part of the problem aren't reading this, so don't anybody here feels personally attacked . .

Well, here's where I think Mike and Samnz are saying the same thing about this . . .

Bon Voyage..!!
Angel

 

Thanks for posting Corley,

I feel sorry for those fellas, but this is what I'm saying, they didn't do a single thing right, if you do it all wrong then you can expect it to go wrong, and their last mistake (going out of the cat) killed them all but one . .

Well, no cheers now...
Angel

 

Some cats could benefit anchoring from the stern to avoid this situation. A bit more windage but no aerodynamic lift..

 

Autodafe,
I'm interested in a pod-type catamaran, where all the living accommodations are in the pod. Since that is the style you have designed too (Autodafe's Pod Cat design) I'm curious where you think your cat will rest when inverted, and how you plan to get out of the (Antarctic?) water? Will you get into your skinny hulls, or will the pod float high enough to provide shelter?

(Not on-topic, but has your design progressed any further?)