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Old 13-09-2019, 03:40   #31
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Re: Hurricane Dismastings when moored

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Originally Posted by ptards View Post
I'm thinking more along the lines of: F=MA
or Force = Mass x Acceleration.
Force in not Energy. Energy is an ability to manipulate things while force is a method of transferring energy.


Once debris is flying, it is no longer accelerating, so F = 0

Or to put to another way, there is no force on the debris.


Now if the debris hits something, it will decelerate , which will result in force on both the debris and whatever it hits (Newton's 3rd Law). The force depends on how much and how quickly it decelerates, which depends on a lot of factors other than the initial velocity of the debris.



The key in this situation is the kinetic energy transfer to the object hit, not the forces involved.
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Old 13-09-2019, 05:46   #32
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Re: Hurricane Dismastings when moored

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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....
Sure it's easy to determine for a single boat...the problem is we need to look at statistical distributions and what the side effects would be before forcing changes.

I'm betting if it was a common problem, insurance companies would have required anti-vortice devices by now. They have adjusters go out and look at the damage and if it was a common failure method, someone would have looked into it.
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Old 13-09-2019, 07:26   #33
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Re: Hurricane Dismastings when moored

Better the mast fail than the boat flip upside down. In any system there has to be a fuse (or bendy part) else at some point you get catastrophic failure.

And monos are pretty similar to cats headed into the wind. I donít think there is any correlation there. I know of at least one Valiant on the hard that lost a mast in Dorian. At 180MPH sustained wind and gusts to 220MPH you donít need flying debris to bring a mast down. There is enough pressure to buckle just about any noodle and sailboat masts are just noodles with stays. We depend on the noodle effect to adjust foresail halyard tension.
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Old 13-09-2019, 07:31   #34
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Re: Hurricane Dismastings when moored

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Better the mast fail than the boat flip upside down. In any system there has to be a fuse (or bendy part) else at some point you get catastrophic failure.

And monos are pretty similar to cats headed into the wind. I donít think there is any correlation there. I know of at least one Valiant on the hard that lost a mast in Dorian. At 180MPH sustained wind and gusts to 220MPH you donít need flying debris to bring a mast down. There is enough pressure to buckle just about any noodle and sailboat masts are just noodles with stays. We depend on the noodle effect to adjust foresail halyard tension.
Good point
Be interesting to know if stays are intact, and mast failed, or if stay failed
Failure looks to be 100% in vids / pics

Aul
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Old 13-09-2019, 08:06   #35
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Hurricane Dismastings when moored

Quote:
Originally Posted by valhalla360 View Post

I'm betting if it was a common problem, insurance companies would have required anti-vortice devices by now. They have adjusters go out and look at the damage and if it was a common failure method, someone would have looked into it.


You would think, but Insurence industry acts on I guess the number of claims, and Iíd guess the number of dismastimg claims without serious damage to the boat is rare.

Now I used to think that it had to be flying debris myself, but how much hull damage is there to flying debris? Iíd say itís rare, but that is just a guess.
But Insurence companies donít require boats to be unsinkable, or even give reduced rates if they are. Again Iíd guess sinkings are rare enough that they donít cause a reaction, or why arenít boats required to be unsinkable?

Iím only saying that a couple of likely reasons for dismastings shouldnít be too hard to determine is all.
I donít think Iíve ever seen a dismasted boat, it happens of course, but probably not very often.
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Old 13-09-2019, 08:06   #36
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Re: Hurricane Dismastings when moored

They called it a tornado, as you see from the caption on the video, but there was some discussion of how accurate that was.

Bottom line .... very powerful air.

You're right that the effect appears to move from left to right in the video (west to east in the harbour). Indeed, a very large car ferry in the basin immediately to the east snapped its lines and went for a wander. But farther east still, there wasn't much, I'm told.

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Old 13-09-2019, 08:20   #37
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Re: Hurricane Dismastings when moored

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What about Don Street's advice? Two days before the storm will hit, sail away to the south.

It is odd it came from Don who as far as I can remember did not have an engine?


It is often pretty windless just ahead of a hurricane. Then when it starts, it starts ... and it is too late to move.


Still, I buy Don's advice. I think it is twice valid today that we all have some form of engine and most sailing boats are de facto motor boats with auxiliary sails.


It is also difficult to say when this '2 days' is, as the systems move at different rates and accelerate / slow down unexpectedly.


Dorian stopped over the Bahamas. When it stops, which way eaxactly is 'away'?



In another hurricanes thread I posted the comment of one Florida mayor who said: "do not get away TOO EARLY, for you may very well escape right INTO its changed path".


But a car is faster than any boat.



So I buy Don's advice even if I have some doubts or limitations.


Move away early, fast, and far away and you will be fine.


Is it not what we do when we sail back to Europe in May?



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Old 13-09-2019, 08:20   #38
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Re: Hurricane Dismastings when moored

Dynamic air pressure on a mast is equal to area facing the wind times air velocity squared times density of air, all else being equal. Wet air at sea level is maximally dense.

Mast or stay pumping causes dynamic pressure to be magnified. Almost all masts have resonant frequencies where they will oscillate. Wrapping halyards around mast helps break up oscillations. Having stays ďtoo tightĒ or ďtoo looseĒ can also affect resonant frequencies and amplitude of oscillations.

Bottom line is when winds reach these speeds no mast can be guaranteed to survive. Itís a random chance thing.
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Old 13-09-2019, 10:11   #39
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Re: Hurricane Dismastings when moored

I know itís counter intuitive, but the higher the relative humidity, the less dense air is
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Old 13-09-2019, 10:29   #40
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Re: Hurricane Dismastings when moored

This paper describes the method used by the Italian Classification Society RINA to develop new Rig Certification Rules.
These Rules have been mostly based on failures observation, and their starting point has been a systematic study of dismastings occurred on boats of various types and sizes.
Examining many of these events, typical collapse modes have been identified, and specific solutions have been proposed.

A NEW APPROACH TO SAILING RIGS CERTIFICATIONhttps://www.researchgate.net/publica..._CERTIFICATION

Just noticed this earlier CF discussion:
http://www.cruisersforum.com/forums/...t-86033-6.html
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Old 13-09-2019, 12:28   #41
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Re: Hurricane Dismastings when moored

It was noted in Marinas on St Maarten during hurricane Irma .... that boats with masts up were worst off and lost their rigging.

Im sure a vessel moored and subjected to a snapping, rolling wave action could well be detrimental to the rigging causing it to fail.

The policy best adopted is to remove all windage.
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Old 13-09-2019, 20:52   #42
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Re: Hurricane Dismastings when moored

Having seen this painful video of a Production Cat, a Fountaine Pajot Lucia 40, from earlier this Nth Hemisphere season, I was surprised how strong the rig was.

https://youtu.be/dqAt18kcljc
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Old 14-09-2019, 02:03   #43
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Hurricane Dismastings when moored

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Originally Posted by hobsonlea View Post
Having seen this painful video of a Production Cat, a Fountaine Pajot Lucia 40, from earlier this Nth Hemisphere season, I was surprised how strong the rig was.



https://youtu.be/dqAt18kcljc
Nice one. Maybe it says more about the thin, light weight hull construction than strength of the rig. I presume the driver is giving it full throttle and the tow is pulling hard. In any event the hulls came up out of the water easily enough.

Guess she also needed new mast top appendages (VHF, windex, anemometer, etc.). And a good hull inspection for stress fractures. Iíll bet the sounds from the hull creaking and groaning was epic.
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Old 14-09-2019, 14:45   #44
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Re: Hurricane Dismastings when moored

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Originally Posted by hobsonlea View Post
Having seen this painful video of a Production Cat, a Fountaine Pajot Lucia 40, from earlier this Nth Hemisphere season, I was surprised how strong the rig was.

https://youtu.be/dqAt18kcljc
Iíll bet his insurers will be insisting on a new front stay before next season

But youíre right, I waited expectantly for the rig to fail. Iím guess there could have been bigger problems staying trapped there with a rising tide.

Good video, thanks.
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Old 14-09-2019, 14:57   #45
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Re: Hurricane Dismastings when moored

...the formulae I read here make me weep
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