Unsinkable multihulls?

[Jacket]

A question for you all. The advocates of multihulls always claim that the advantages of multihulls is that they're unsinkable.

OK, so if you turn one over it will trap air in the hull, and keep floating. But in a monohull you'd pop back up, so you're definitely better off.

Now if you hit a container, surely a multihull will fill up with water and sink like anything else, unless its got foam buoyancy or similar to stop it sinking. And as far as I know, few of the production builders seem to fit flotation, unless I've missed something? Certainly, after this years hurricanes, there's been plenty of pictures of sunken multihulls.

So surely you're worse off either way in a production multihull than you would be in a monohull?

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[mirabriani]

Ho Ho Jacket!
Now sit back and enjoy the thread!

You would not by any chance like another sand yacht would you?

Regards Briani

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[Goodge]

I think this depends on how the potential sinking accident has happened.

One important thing you're forgetting is that multihulls have large saloon areas which will give a lot of buoyancy.

If say you strike an underground object you may damage one hull and the water floods in. However you still have the buoyancy from the other hull and the saloon area.

If you flip it, I would suggest not that likely in a cruising cat, then the saloon may fill up but you have buoyancy from the two hulls to keep her up.




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[mirabriani]

I have a book "Capsized" by James Nalekpa and Stephen Callahan published by Harper Collins
Four men in a trimaran capsized four days out and drifted for fours months before ending up back in New Zealand.
It is a very good read

Regards Briani

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[Goodge]

Thanks for that I'll put it on the Xmas list.

Proves the unsinkable theory then ?

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[mirabriani]

Only until it came to rest on the Great Barrier Reef

Regards Briani

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[Talbot]

I would have to be travelling very fast indeed for a collission with a container to sink me. The underwater shape would encourage riding up and onto the container, Should it damage the bow, there is a waterproof compartment in the fwd 2ft of each hull, which is full of closed cell foam, there is another 2 ft then you come to another bulkhead which could be sealed. Each hull is divided up into four watertight compartments, the biggest could be further subdivided if you were really paranoid.

Of course a sideways impact that opened up several compartments would probably sink her, but even then the difference is that the boat would not sink like a stone (like a monohull that had suffered the same damage), but would slowly fill up and gracefully slide under giving enough time for the occupants to prepare.

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[mirabriani]

Erm, How would it fair if, God forbid, it scraped against an iceberg?

Briani

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[Gordonmc]

Would have thought the biggest factor in the bouyancy of any boat would be the several tons of lead/pig iron/railway sleepers etc carried as ballast.
Multihull - not much.
Monohull - a heap.

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[Goodge]

Titanic was a monhull.....nuff said ?

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[Talbot]

How would it fair if it scaped against an iceberg - I knew someone would ask that which is why I wrote:
<font color=blue>Of course a sideways impact that opened up several compartments would probably sink her, but even then the difference is that the boat would not sink like a stone (like a monohull that had suffered the same damage), but would slowly fill up and gracefully slide under giving enough time for the occupants to prepare.
</font color=blue>
Personnally I thinnk the possibility of this is so remote as to be non-existant. I dont have a big keel holding me from moving sideways, thus an impact on the side would merely deflect the boat sideways, which is why heaving to is a total waste of time

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[mirabriani]

Yes. Checkmate to you
Briani

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[Birdseye]

Modern multihulls are unsinkable for 2 reason - they dont carry 40% of their weight around as ballast, so they are much lighter size for size than monos. The second factor is that modern multis are all foam sandwich, so even the laminate is lighter than water. Were you to take a hose and totally fill the hulls with water, they still wont usually sink. Try that with a mono (apart from either Gibsea or Feeling, one of which is also unsinkable)

You are a bit less likely to hole them on a floating container because the laminates tend to be more hi tech (as in kevlar, carbon fibre etc) but mainly because you have far less momentum when you hit something solid, because you weigh less. Finally, most modern multis have crash bulkheads in the bows which also helps. True the motivation for this is as much to stop pople putting payload into the bows as anything else but it helps.

Many modern monos which capsize (itself far more likely in a mono than a cat for reasons of basic physics) are quite stable inverted. An AVS of 120 deg is not unusual - which means that when the boat goes past 120 deg it is becoming stable upside down. Just like Bullimore did. Of course, being heavier than water and after sustaining damage during a roll (or simply having washboards drop out) a mono could well sink - that ballast again. So the choice may well become upside down but floating in the cat, or right way up but sunk in the mono.

There are some good reasons for chosing a mono over a cat, but in my view safety isnt one of them.

<hr width=100% size=1>this post is a personal opinion, and you should not base your actions on it.

 

[mirabriani]

On another thread I have just recomended a book called Capsized by James Nalepka and Steven Callahan published by Harper Collins.
A true story about a trimaran which capsized four days out and drifted back to New Zealand four months later. The latter co author also wrote Adrift.
Just to show I am not biased, it may help your argument regarding multi hulls.

Regards Briani

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[Twister_Ken]

Taking it to extremes

>If say you strike an underground object <

What, like Oxford Circus tube station?

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[Birdseye]

Re: Taking it to extremes

Monos often do hit undergound objects - on the bottom! /forums/images/icons/smile.gif

<hr width=100% size=1>this post is a personal opinion, and you should not base your actions on it.

 

[Twister_Ken]

Re: Taking it to extremes

If it is on the bottom it can't be underground, only underwater.

Mind you there's a ticket collector at Russell Square with a very pert little ...

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[mirabriani]

On a mooring near to me is a trimaran with folding floats (A Tristar I think)
It is a drying mooring and the regular crew claims to be able to sail 30% further than the mono's on the tides.
However he also conceded that he would not wish to be "Too far out in a blow"
because it is light and he would be concerned for the security of the floats.

Regards Briani

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[mirabriani]

Sorry it was this thread
A senior moment methinks
Briani

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[Talbot]

Dont really have an argument about it. Multihull is my choice for the reasons that I am happy about. If other people want other boats (motor or sail) for their on reasons, thats fine by me. Would be a horrible world (and dammned confusing in a marina) if we all wanted exactly the same boat /forums/images/icons/smile.gif



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