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Old 12-09-2019, 04:53   #16
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Re: Hurricane Dismastings when moored

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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..
Wind force on a stationary object increases by the square of the wind speed. 180 mph plus turbulent gusts or embedded tornadoes. Quite possible there were extreme loads even without debris. Add in a chunk of wood ant the impact could buckle a spar.
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Old 12-09-2019, 05:51   #17
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Re: Hurricane Dismastings when moored

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I donít believe itís a Cat thing either, it seems even monoís lose theirs too.
Two theories that in my opinion that have merit have been proposed here.
One has been stated and itís in my opinion most likely, the flying debris theory.
Another is that the masts get into a harmonic, think galloping Gertie the bridge. I wouldnít have believed that but Iím 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.
Agree. Ive seen monos dismasted at dock in severe weather. A mono in particular, with no sails up to dampen rolls, can develop a really ugly snap roll in beam seas.

I think there are just so many cats in the carib now, that those are the images you see most often.

I think Ive still got a pic, will try to find, of a mono that dismasted at dock in strong tropical storm (just under hurricane) conditions...the entire rig fell on the boat next door. [emoji26]

During the golden era of sail, there are accounts of tall ships being dismasted after storms when winds went light, but seas still big. I read one account where captain deliberately cut the rig down because it was failing and threating to damage the hull.
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Old 12-09-2019, 06:20   #18
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Re: Hurricane Dismastings when moored

Come on, no one has said it yet...once the monos are on the bottom, they experience very little wind effect on their masts.

I suspect the flying debris is the real answer but so far no statistical evidence cats lose masts at a greater rate (of course a picture of a charter base with 90% cats will show more cats with lost masts...there simply aren't many monos).
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Old 12-09-2019, 06:28   #19
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Re: Hurricane Dismastings when moored

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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)
I wasn't remotely questioning catamaran design. It was just eery to see large boats so high off the water on rooftops around Sopers Hole. If design had anything at all to do with it, cats fly better than monos? For what it's worth, quite a few buildings flew just as well.
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Old 12-09-2019, 06:34   #20
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Hurricane Dismastings when moored

Ref the vortices. Many fixed car antennas have if you look a small wire wrapped around the antenna itself in a spiral. Without it the antenna can shake violently.
If itís this, I wonder why masts arenít manufactured with a spiral wrap to prevent the vortices?
As Gord suggests, a halyard might be enough to break up the vortices.
Taller and therefore less stiff masts would be more vulnerable.
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Old 12-09-2019, 06:41   #21
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Re: Hurricane Dismastings when moored

Wind alone can do a lot of damage in a short time. Westhaven Marina in Auckland got hit recently by a very short but very powerful storm.



This stuff, from a fixed surveillance camera, I think, repeats itself, but you see early on a catamaran flipped out of its slip and right over the pier. Shortly thereafter, one of the large yachts puts its four-spreader mast in the water, snapping its docklines in the process.

Luckily no one was aboard the cat. There were crew aboard the yacht, who were able to start engine and motor out into the harbour, with no injuries reported.

My point is that all happened in a few minutes. If that force had been sustained, the damage would have been enormous. And in the Bahamas the force was sustained, so it's no wonder cats flipped and boats lost their rigs.

Maybe that was because things were flying -- probably was -- but wind alone could have done a lot of the damage.

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(The effects were extremely localized. The cat was on Y pier; Above the Fold, our Wright 10 sloop) is on L pier and suffered not at all.)
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Old 12-09-2019, 06:53   #22
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Re: Hurricane Dismastings when moored

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Originally Posted by mabowers View Post
I wasn't remotely questioning catamaran design. It was just eery to see large boats so high off the water on rooftops around Sopers Hole. If design had anything at all to do with it, cats fly better than monos? For what it's worth, quite a few buildings flew just as well.

Unless the monos are the latest America's Cup contenders
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Old 12-09-2019, 06:55   #23
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Re: Hurricane Dismastings when moored

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Originally Posted by a64pilot View Post
Ref the vortices. Many fixed car antennas have if you look a small wire wrapped around the antenna itself in a spiral. Without it the antenna can shake violently.
If itís this, I wonder why masts arenít manufactured with a spiral wrap to prevent the vortices?
As Gord suggests, a halyard might be enough to break up the vortices.
Taller and therefore less stiff masts would be more vulnerable.
Probably because it's very rare failure mode.

Most steel/aluminum street poles are tapered for this reason. It has a similar effect. There is a particular wind speed for a pole width that resonates...by using a taper, the wind can only resonate a tiny section of the pole.

Difference is poles are put up with minimal maintenance for decades. Sailboats should have the rigging looked over at least annually. Also, poles are bought by the thousands as standard sizes. Masts are often a standard cross section but cut to length before fitting out on the boat.

Before we change mast design, we need to show there is a problem to solve.
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Old 12-09-2019, 09:52   #24
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Re: Hurricane Dismastings when moored

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Originally Posted by valhalla360 View Post
... Most steel/aluminum street poles are tapered for this reason. It has a similar effect. There is a particular wind speed for a pole width that resonates...by using a taper, the wind can only resonate a tiny section of the pole...
Indeed.
See also (1ST and 2ND mode vibration) ➥ http://www.cooperindustries.com/cont...-paper-bro.pdf
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Old 12-09-2019, 10:01   #25
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Re: Hurricane Dismastings when moored

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Agree. Ive seen monos dismasted at dock in severe weather. A mono in particular, with no sails up to dampen rolls, can develop a really ugly snap roll in beam seas.

I think there are just so many cats in the carib now, that those are the images you see most often.

I think Ive still got a pic, will try to find, of a mono that dismasted at dock in strong tropical storm (just under hurricane) conditions...the entire rig fell on the boat next door. [emoji26]

During the golden era of sail, there are accounts of tall ships being dismasted after storms when winds went light, but seas still big. I read one account where captain deliberately cut the rig down because it was failing and threating to damage the hull.
Found the image. The waves got ugly in the marina and this boat was dismasted in its slip. After the storm it was still tied up in its slip..sans mast.

There was no flying debri capable of inflicting this kind of damage, but the boat was rolling violently during the storm. I saw it when it was snap rolling, but missed the actual moment of dismasting.


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Old 12-09-2019, 12:18   #26
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Re: Hurricane Dismastings when moored

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Originally Posted by Connemara View Post
Wind alone can do a lot of damage in a short time. Westhaven Marina in Auckland got hit recently by a very short but very powerful storm.







This stuff, from a fixed surveillance camera, I think, repeats itself, but you see early on a catamaran flipped out of its slip and right over the pier. Shortly thereafter, one of the large yachts puts its four-spreader mast in the water, snapping its docklines in the process.



Luckily no one was aboard the cat. There were crew aboard the yacht, who were able to start engine and motor out into the harbour, with no injuries reported.



My point is that all happened in a few minutes. If that force had been sustained, the damage would have been enormous. And in the Bahamas the force was sustained, so it's no wonder cats flipped and boats lost their rigs.



Maybe that was because things were flying -- probably was -- but wind alone could have done a lot of the damage.



Connemara



(The effects were extremely localized. The cat was on Y pier; Above the Fold, our Wright 10 sloop) is on L pier and suffered not at all.)


You know when the Cat flipped then a few seconds later the Mega got knocked down, sure makes it look like a tornado.
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Old 12-09-2019, 16:03   #27
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Hurricane Dismastings when moored

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Originally Posted by valhalla360 View Post



Before we change mast design, we need to show there is a problem to solve.


Iíve been trained and participated in a few aircraft accident investigations.
How these masts failed would be easy to determine, or at least rule out failure modes.
If from an impact, there would be evidence of impact damage right at the failure point, it should be pretty obvious.
If the mast came down from a rig failure, then of course the rig will be broken.
But if you donít find impact damage and the rigging isnít broken, then itís likely it was due to something else.
Itís true that aeroelastic flutter could fail the rig and that cause the mast to fail, I believe the mast would go first, if the rig was in excellent shape and not fatigued.

I feel that the mast may get into a flutter mode, caused by the shedding of the vortices.

In fact I believe it happens all the time, just not at an accelerating amplitude that leads to failure as the winds arenít high enough, havenít we all felt our masts begin shaking in high winds?
https://youtu.be/OhwLojNerMU

Very good friend of mine, Ralph was my mentor.
What stood out about this crash was it was the either 5th or 7th time the aircraft had been dove to VD, velocity dive speed and of course it never got into flutter, until this time.
Interval from the onset of flutter to empennage disintegration was less than 1 sec. North American Rockwell duplicated the accident in their wind tunnel.
https://aviation-safety.net/wikibase/2731
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Old 12-09-2019, 16:37   #28
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Re: Hurricane Dismastings when moored

Good thread.


One reason is the alloy mast extrusion pumping. You are right extra stays may prevent this. No need for spectra as it is all about changing the harmonics.


With stay foils e.g. a tape is flown to spoil the flow and avoid pumping.



I am surprised this happens on cats as I was told many times cat masts are built thicker due to the boat's specific dynamics.


Have seen Bavaria and other mass hysteria mono hull boats masts pump wildly in as little as 40 kts of wind.


b.
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Old 12-09-2019, 17:31   #29
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Re: Hurricane Dismastings when moored

What about Don Street's advice? Two days before the storm will hit, sail away to the south.
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Old 13-09-2019, 03:12   #30
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Re: Hurricane Dismastings when moored

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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 )
I'm thinking more along the lines of: F=MA
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