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Old 19-12-2010, 16:42   #31
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Physics..

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Originally Posted by boden36 View Post
It's true then, that a cat of that size can flip after colliding with a semi-submerged object in relatively calm conditions???
Regards, Richard.
I'd say that a capsize caused by collision has more to do with the laws of physics than size, design etc. In particular if the crew were running under spinnaker this would (I believe) only accentuate the 'fulcrum' effect when the waterline of the boat stops immediately and the mast and sails continue to travel forward powered by the wind thereby initiating a capsize (unless of course the crew have time to cut the sheets).

Thanks,
Les
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Old 20-12-2010, 05:52   #32
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Catty, you question the boat striking the container off the side - why? You refer to it as a 'glancing blow', whereas the article you site refers to a 'violent impact' causing a 6 meter hole! Why? For those who have read your contributions in the past (and your consistent efforts at denigrating catamarans) the reason is pretty obvious.

It was not a personal attack - as far as I know you are a very nice (and I suspect quite bright) person who just has an averson to catamarans and is prepared to stretch (or mis-state) the facts in order to advance your postion.

Brad
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Old 20-12-2010, 06:55   #33
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It surprises me that no one has mentioned immersion of one hull as a cause of capsize, or at least a major contributor. A two meter hole would allow pretty free ingress of water, sort of like the prior post about a mono going down in seconds from a similar collision.
Probably takes very little to capsize a multi once one hull fills with water, providing very limited flotation, if any. A breech that size could easily flood the bridgedeck, which would make it prone to capsize in benign conditions, not to mention the 2 meter seas and 25 knot winds the skipper observed.
Had they been in a monhull, there would have been no going back into the boat to recover epirb, etc.
I am just glad that all were saved and the boat may be recovered.
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Old 20-12-2010, 14:13   #34
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Originally Posted by Southern Star View Post
Catty, you question the boat striking the container off the side - why? You refer to it as a 'glancing blow', whereas the article you site refers to a 'violent impact' causing a 6 meter hole! Why? For those who have read your contributions in the past (and your consistent efforts at denigrating catamarans) the reason is pretty obvious.

It was not a personal attack - as far as I know you are a very nice (and I suspect quite bright) person who just has an averson to catamarans and is prepared to stretch (or mis-state) the facts in order to advance your postion.

Brad
Brad, Its probably best to stop digging once your in a hole.
You obviously have difficulty understanding my posts as if you read carefully you would have noted I am a long term multihull owner /cruiser / racer/and builder, but hey, I obviously have trouble distinguishing your post from informative or personal attacks.

The news release regarding the 2 meter hole came after my initial post. Please reread the posts in order and all will become clear.


Being confident in my choice of vessel allows me to question the warts and all aspects, such as capsize, in the hope I can learn more. Maybe others new to multihulls such as your self will allso learn from the ensuing discussiions. Hopefully brad, one day you will also be as comfortable with your choices.

Rergards.
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Old 21-12-2010, 00:21   #35
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What design cat do you sail catty and what do you think are its strengths and weaknesses.
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Old 21-12-2010, 01:08   #36
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If anyone has watched those car stunt drivers who use a ramp to get two wheels off the ground and drive around on the other two wheels then you would know that the right force at the right time can have amazing results. So, based on almost total assumption, I could imagine one hull of a cat hitting at speed a very solid object "sitting below the surface" with enough force to rip a "two metre hole" could if angles were right possibly generate sufficient lift to jump the hull up out of the water rather than stop it dead. Furthermore, it is possible (another assumption) that the "25 knot winds" and the way the sails were set then aided the flipping over of the cat. While the container being at exactly the right depth and hit in exactly the right way and having the sails set in exactly the right way for the cat to flip as outlined here may be statistically highly improbable, odder things do happen. The flip may just be a fluke.

Now, if the boat they were in happened to be a monohull, they may have missed the object altogether. Since the object was on a collision course with one of the two hulls of the catamaran, by only having one hull, this would reduce the chance of impact by 50%. : ). On the other hand, with one hull holed, the cat still had one hull intact and lots of flotation but a monohull with a two metre hole in it . . . .
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Old 21-12-2010, 05:26   #37
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It's just simple probability. Right now there are far fewer cruising multis than monos, but as/if the numbers even out, you'll hear about more such incidents.
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Old 21-12-2010, 13:56   #38
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Sneuman's right. Probability. Two hulls equals double the chance of collision! (Balanced of course by double the chance of staying afloat!!)
Regards, Richard.
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Old 21-12-2010, 13:58   #39
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Sneuman's right. Probability. Two hulls equals double the chance of collision! (Balanced of course by double the chance of staying afloat!!)
Regards, Richard.
Does that mean that a 60ft mono is twice the chance of hitting something asa 30foot mono - or indeed the same as a 30 ft cat?
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Old 21-12-2010, 14:08   #40
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Does that mean that a 60ft mono is twice the chance of hitting something asa 30foot mono - or indeed the same as a 30 ft cat?
Goes on frontal cross section. So a 60 foot mono would be unlikely to have 2x frontal cross section of a 30 foot mono. But that's not all. Any formula to work out risk would need to take into account how much beer and stuff was on board since that would affect how deeply the hull was settled in the water. However, if the crew were trying to lighten the load, that is, reduce the amount of hull under water, by drinking their way through the liquid provisions, perversely, the risk of the boat hitting something is likely to increase not decrease.
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Old 21-12-2010, 14:10   #41
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So should we be working out the cubic volume in the water - eg 60ft mono would likely be much deeper and displace much more water?
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Old 21-12-2010, 14:18   #42
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So should we be working out the cubic volume in the water - eg 60ft mono would likely be much deeper and displace much more water?
Probably best to just to use swept surface area as when looking at the front aspect of the boat below the waterline. The deeper displacement of a mono is more obvious from the side aspect but underwater collisions from this direction are usually limited to navy submarines and blind whales. Thus side area or even cubic volume is of lesser value in calculating risk factors than the frontal profile.
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Old 21-12-2010, 14:30   #43
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Only true if you are looking at collisions with floating objects. Mono's with their greater draught are far more likely to hit submerged objects ie. the bottom.

But even looking at frontal area, my 44' cat has a BWL of 1.2 metres, (per hull) do many 44' mono's have a BWL of less than 2.4 metres?

Mono or multi, you still have to be unlucky to hit a floating container though.
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Old 21-12-2010, 15:10   #44
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Mono or multi, you still have to be unlucky to hit a floating container though.
I agree. The chances of hitting a floating container would have to be so slim that it would be way down any list of sailing risks, not worth worrying about. My previous comments have been tongue-in-cheek and not meant to be taken seriously.
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Old 21-12-2010, 15:53   #45
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I really can't understand the attitude of some people towards cats in this thread. There seems to be some sort of 'anti cat' feeling from monohull people that seem to enjoy implying that the basic twin hull of a cat' is a dangerous or flawed design. Sure it capsized BUT it stayed afloat. The fact that it hit the thing is nothing to do with the design, if it was a monohull that hit it, it would have undoubtably sunk altogether. I bet that there have been similar incedents in the past involving monohulls and I bet that there were no cat' owners saying "ah that's because it was a monohull....".

So what's going on, multihull envy?
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