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Old 04-09-2019, 23:50   #1
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Hurricane Dismastings when moored

Pictures of Dorian show several floating catamarans, dis-masted

Seems common from the last big hurricanes.

It makes me wonder why (assumptions) bare rigs all come down.

And if this could be prevented in any way, perhaps using dyneema secondary stays during events.
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Old 04-09-2019, 23:58   #2
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Re: Hurricane Dismastings when moored

I think it's more than likely that something hit the masts. The amount of debris and bits of roof flying around is going to remove any mast and any amount of dyneema.
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Old 04-09-2019, 23:58   #3
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Re: Hurricane Dismastings when moored

Can you send us the photos of these dismasted catamarans
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Old 07-09-2019, 14:26   #4
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Re: Hurricane Dismastings when moored

Even accepting the urban myth (true/not true matters not) that modern mass produced cats will lose their rig before a capsize, i most sincerely doubt that even with 180mph winds that sufficient force could go on a bare rig to demast a cat.

flying debris?... i suspect that @Tillsbury is correct as I suspect even a simple fence post at 180mph would take out a rig..
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Old 07-09-2019, 14:35   #5
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Hurricane Dismastings when moored

I don’t believe it’s a Cat thing either, it seems even mono’s lose theirs too.
Two theories that in my opinion that have merit have been proposed here.
One has been stated and it’s in my opinion most likely, the flying debris theory.
Another is that the masts get into a harmonic, think galloping Gertie the bridge. I wouldn’t have believed that but I’m sure we all have felt our masts shake in higher winds, so maybe?

Debris wise I think it would take very little, a mast is a tube in compression of course, knock a dimple in it and it will likely collapse.
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Old 07-09-2019, 14:59   #6
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Re: Hurricane Dismastings when moored

Quote:
Originally Posted by Mystic38 View Post
Even accepting the urban myth (true/not true matters not) that modern mass produced cats will lose their rig before a capsize, i most sincerely doubt that even with 180mph winds that sufficient force could go on a bare rig to demast a cat.

flying debris?... i suspect that @Tillsbury is correct as I suspect even a simple fence post at 180mph would take out a rig..
Except that mast on cats offer a lot more resistance to wind than monohulls simply through their inability to heel. Most cruising cats are (relatively speaking) quite heavy and will stay reasonably flat even with severe pressure on the mast.

And whilst I’m not a cat expert, my perception is that on big cats, the mast sections are quite large (?) offering more resistance.

This is one of the reasons (IMHO) why marine insurers are now asking for 10-year standing rig replacement. Cruising cats that strongly resist heeling impose far greater stresses on standing rigging than monohulls that yield to the pressure do. Hence potential for rig failure is accentuated and insurers always like to mitigate risk and use worst-case scenarios to do that. So we all get to pay more.

Tillsbury has a point except that flying debris is just as likely to destroy masts on other boats, not just cats. Any stationary mast in the path of a 180mph fence post is likely to take considerable strain

As far as using Dyneema to improve strength, in this case I believe it would not work. Whilst I understand that Dyneema may be equal in strength to stainless wire, it doesn’t have equal cut-resistance and in the face of flying 180mph debris . . . .

Disclaimer: I say the above having not seen the images nfbr mentions, perhaps the dismasted vessels were not all cats.
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Old 07-09-2019, 15:00   #7
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Re: Hurricane Dismastings when moored

Quote:
Originally Posted by Tillsbury View Post
I think it's more than likely that something hit the masts. The amount of debris and bits of roof flying around is going to remove any mast and any amount of dyneema.
Ron White explains this pretty well...
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Old 07-09-2019, 15:14   #8
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Re: Hurricane Dismastings when moored

I was in BVI 6 months after Irma, I saw a lot of dismasted cats, and a lot of monohulls on the beach. Of course, there were also quite a few cats upside down on top of buildings 100 yd away from water. The idea of catamarans flying like giant frisbees makes me shiver still...
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Old 07-09-2019, 16:53   #9
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Re: Hurricane Dismastings when moored

Quote:
Originally Posted by a64pilot View Post
... Two theories that in my opinion that have merit have been proposed here.
One has been stated and it’s in my opinion most likely, the flying debris theory.
Another is that the masts get into a harmonic, think galloping Gertie the bridge. I wouldn’t have believed that but I’m sure we all have felt our masts shake in higher winds, so maybe?

Debris wise I think it would take very little, a mast is a tube in compression of course, knock a dimple in it and it will likely collapse.
I agree.

Kármán vortex*:
Wrap your halyard(s) around the mast, in a spiral, and draw tight, to prevent the formation of Kármán vortex sheets downwind of the mast.
It works by diverting the wind upwards on one side of the mast, and downwards on the other, creating a three-dimensional airflow pattern that disrupts the vortex sheet. Without them, the vortex shedding could cause vortex-induced vibration in the mast, which, in strong winds, might be enough to damage the (relatively thin-walled and flexible) mast.
It Really Works!
Mast Pumping - Is This Normal?

* See Step 4 Fixing the problem
http://www.spartaengineering.com/vor...ll-structures/
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Old 12-09-2019, 00:46   #10
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Re: Hurricane Dismastings when moored

Some pics / vids - Most / all masts are fallen

https://www.facebook.com/Rosanne26/p...19816107661205

https://www.youtube.com/playlist?lis...CaaEORgTbTud58

https://photos.google.com/share/AF1Q...dwUlk2Wmd2Ykln
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Old 12-09-2019, 01:11   #11
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Re: Hurricane Dismastings when moored

[QUOTE=mabowers;2971576...The idea of catamarans flying like giant frisbees makes me shiver still...[/QUOTE]

Hardly fair to question catamaran design on the basis of their taking flight during Irma, there were shipping containers and pick-up trucks going airborne in that one.

As to the OP, as stated by others, almost all will have been casualties of flying debris, it doesn't need anything as substantial as the 'fence post' mentioned, it's the speed of the impact that counts (E=MC2 applies, even when it's not quite at light-speed)
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Old 12-09-2019, 01:41   #12
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Re: Hurricane Dismastings when moored

Quote:
Originally Posted by bobnlesley View Post
As to the OP, as stated by others, almost all will have been casualties of flying debris, it doesn't need anything as substantial as the 'fence post' mentioned, it's the speed of the impact that counts (E=MC2 applies, even when it's not quite at light-speed)
No it doesn't.
E=MC˛ is an entirely different concept, it just happens to look similar to the appropriate equation.



In this case, you are talking about Kinetic energy (K.E)

Presumably, you are thinking of the equation K.E. = 1/2 mv2


(Don't ask why the 1/2 is in there unless you want a treatise on the calculus form of Newton's Second Law of Motion )
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Old 12-09-2019, 03:22   #13
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Re: Hurricane Dismastings when moored

A boat (mono around 12/14m) lost it's rig while anchored in Majorca two days ago. Wind peaked at 85 kts.
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Old 12-09-2019, 04:28   #14
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Re: Hurricane Dismastings when moored

Here in Bermuda we actually don't get that much flying debris during hurricanes but boats still often lose their masts. Very interesting to hear that stuff about vortexes (or is it vortices?).

One of the leading causes is failing to remove a roller-furling headsail. Even a tightly-rolled headsail can be pried free by the wind. Then either the mast comes down from the violent shaking or the boat breaks free from the mooring from the increased load.
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Old 12-09-2019, 04:33   #15
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Re: Hurricane Dismastings when moored

In 1998 I first heard the term micro burst following a storm that dismasted three boats at anchor in our home port.

Not catamarans, no flying debris- wind did that.
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