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Old 28-01-2010, 22:58   #16
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To all,

Further to my original post ...


How does one recognize ... and differentiate ... between: (1) frontal squalls, (2) microbursts/downdrafts, and (3) "white squalls?"

I've heard that the so-called "bulls-eye squall" occurs only off the coast of South Africa and in Nova Scotian waters. Truth or fallacy?

Lastly, what about an incipient waterspout while the funnel isn't readily visible? What about encountering a fully developed 'spout at night? Aren't they too small and transient to appear on radar?

Thanks.
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Old 29-01-2010, 02:45   #17
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With radar it's not that big a deal, we've raced through many with sustained winds of 80 or so.
Is the above sustained wind speed a typo ? If its not a typo, guess it was in an aircraft?
80 knots sustained means gusts achieving 112 knots !
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Old 29-01-2010, 05:50   #18
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How does one recognize ... and differentiate ... between: (1) frontal squalls, (2) microbursts/downdrafts, and (3) "white squalls?"
"White Squall" is a term that describes the appearance of some microbursts (i.e. sudden strong wind, with no tell tale no black cloud). A microburst is a sudden downdraft that spreads when it hits the surface.
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Old 29-01-2010, 06:08   #19
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Well, one of fronts we raced through knocked down a cinder block wall at the malls movie theater when it reached shore.

It was kind of windy.

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Is the above sustained wind speed a typo ? If its not a typo, guess it was in an aircraft?
80 knots sustained means gusts achieving 112 knots !
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Old 29-01-2010, 06:45   #20
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The vertical winds (downdrafts) are the only winds that can capsize a monohull. I would be horrified when I would have to deal with regular squalls on a catamaran because it refuses to heel and spill the wind, resulting in enormous stresses on the rig. That is why cat-sailors lower all sails before the squall hits... imagine you didn't see one coming at night. With downdrafts, I wonder how far down cats are pushed with all that horizontal surface! But they probably already flipped at that point...
Monohulls on the other hand just heel, spill the wind that way and sail on. They are just better and skippered by real sailors ;-))

Back to serious: Many believe that white squalls and the Bermuda triangle are related to this downdraft phenomena. The square rigged ships do really bad in these conditions.

If I would see a black or white menace coming, I would drop all sails too, steer downwind and just hold on. But in 7 years Caribbean, we only did that once (Aruba) and the reason wasn't the wind but the waterspouts right in front of us.

Waterspouts: steered away from them all my life, incl. in Holland (ie. they are everywhere many we saw in the Caribbean were much much bigger than in the EU). I understand that boats that get hit shred their sails but survive better than expected.

ciao!
Nick.
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Old 01-02-2010, 22:21   #21
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Is the above sustained wind speed a typo ? If its not a typo, guess it was in an aircraft?
80 knots sustained means gusts achieving 112 knots !
Around mid-January, we had a line of squalls associated with a front come through the marina at St Augustine, FL. A number of boats lost their canvas and large plastic trash cans were flying horizontally accross the marina - Learned the next day that the office anemometer registered 70 knot winds sustained for about 15 to 20 mins - if this were offshore, I am sure it would been one of those religious experiences As it was, I was able observe in awe with a beer in my hand, safely tied to the dock

Shamrock, it looks like you could benefit from obtaining a copy of 'Mariners Weather' by William P. Crawford or something similar. In the book, it provides thorough and understandable descriptions of the weather systems, including a very good description of the profile of a squall.

Understanding the profile of a squall, you'd be able to gauge where you are with respect to the center of the squall and which way to steer to minimize your exposure. On a grander scale, this also applies to cyclones.

'Fair' winds to all!

Sailndive
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Old 11-02-2010, 11:47   #22
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"White Squall" is a term that describes the appearance of some microbursts (i.e. sudden strong wind, with no tell tale no black cloud). A microburst is a sudden downdraft that spreads when it hits the surface.
Ziggy,

Just to confirm ... so a "white squall" and a microburst are essentially one and the same beast?

Thanks.
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Old 11-02-2010, 13:27   #23
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The vertical winds (downdrafts) are the only winds that can capsize a monohull. I would be horrified when I would have to deal with regular squalls on a catamaran because it refuses to heel and spill the wind, resulting in enormous stresses on the rig. That is why cat-sailors lower all sails before the squall hits... imagine you didn't see one coming at night. With downdrafts, I wonder how far down cats are pushed with all that horizontal surface! But they probably already flipped at that point...
Monohulls on the other hand just heel, spill the wind that way and sail on. They are just better and skippered by real sailors ;-))
Nick,

Pardon my ignorance but I thought that multi-hull 'cats' would (a) survive horizontal squall-type winds better than mono-hulls since their greater beam would resist capsizing ... assuming her sails were furled; (b) they would be more vulnerable to the vertical fall winds of a microburst due to their greater beam. Yes? No?

In the case of (b) would a multi-hull be driven down into the water or the sheer weight of such wind-force even tear her asunder?

Care to elab on all this?

Thanks.
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Old 11-02-2010, 14:03   #24
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Shamrock, it looks like you could benefit from obtaining a copy of 'Mariners Weather' by William P. Crawford or something similar. In the book, it provides thorough and understandable descriptions of the weather systems, including a very good description of the profile of a squall.

Understanding the profile of a squall, you'd be able to gauge where you are with respect to the center of the squall and which way to steer to minimize your exposure. On a grander scale, this also applies to cyclones.
Sailndive345,

Yes, I've been checking the local libraries and came across the Crawford book and some others as well. Good reads!

Thanks.
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Old 11-02-2010, 14:40   #25
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Pardon my ignorance but I thought that multi-hull 'cats' would (a) survive horizontal squall-type winds better than mono-hulls since their greater beam would resist capsizing ... assuming her sails were furled; (b) they would be more vulnerable to the vertical fall winds of a microburst due to their greater beam. Yes? No?

In the case of (b) would a multi-hull be driven down into the water or the sheer weight of such wind-force even tear her asunder?
Shamrock,
a) IMO, even with the sails down, the windage of many cruising multihulls is sufficient to have them lift a hull above water in case of a strong horizontal squall. This increases the risk that the wind blows under the deck and this pressure capsizes the boat. Some 25 years ago, "Elf Aquitaine II", a French blue-water racing catamaran, capsized in harbor with all sails down when a regular gale got hold of her wing-mast, which could not be reefed.

As a precaution against this, some multihulls are designed in such a way that shrouds will part and the mast comes down before the boat capsizes.

b) Close to the water surface, a "vertical" downburst is forced to spread horizontally. Otherwise, air would penetrate water. Then, I can't see how the wind could drive a boat underwater.

Alain
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Old 12-02-2010, 10:54   #26
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Nick,

Pardon my ignorance but I thought that multi-hull 'cats' would (a) survive horizontal squall-type winds better than mono-hulls since their greater beam would resist capsizing ... assuming her sails were furled; (b) they would be more vulnerable to the vertical fall winds of a microburst due to their greater beam. Yes? No?

In the case of (b) would a multi-hull be driven down into the water or the sheer weight of such wind-force even tear her asunder?

Care to elab on all this?

Thanks.
No, mono-hulls can cope with horizontal winds because they heel and reduce the windage that way. This is an automatic protection. A cat on the other hand, does not heel so the full force of the wind is being absorbed by the mast & rigging. If that would be strong enough, the cat will capsize, something a monohull will never do (only waves can capsize a mono).

With sails up both cat and mono are in deep trouble with vertical winds. You just don't want that to happen. With sails down both will be fine I think... I hope you know I was joking a bit in my previous post ;-)

cheers,
Nick.
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Old 11-01-2011, 06:10   #27
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Question so??

so what do u do, furl and turn into the wind?? peace of cake ain't it? a bit of power or a drouge????
peace!
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Old 11-01-2011, 12:26   #28
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IMO a downdraft typically comes of the lee side of a cliff or mountain / hill and you cannot see it until it suddenly hits the water.

Off the south coast of the Isle of Wight such a downdraft laid my 6m monohull flat for about 30 seconds with the mast touching the water. Upon righting we had 600 litres of water in the boat!

And a friend of mine was sailing off Cape of Good Hope in False Bay under the range of mountains in his 8m catamaran. There was no wind and he was just about to turn on the engine when a downdraft hit and capzided them in 3 sconds flat! All four people survived, one mast broke when it hit the water on impact. Since then he has found out that this particular strech of the bay is locally called "Hurricane Alley" and he now stays well clear of that area.

In both cases no ripples on the water were to be seen beforehand.

I am VERY wary when my course takes me close to a high headland in an offshore wind ever since.
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Old 27-01-2011, 14:48   #29
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Avoidance = Stay in port
Confrontation = Sea anchor
Survival = Batten down the hatches and pray the boat you bought is worthy of praise.
Preparation = Brown pants
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Old 27-01-2011, 19:38   #30
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In plain weather probably just drop the sails and wait.

In otherwise severe weather probably just keep on going and try not to break anything.

Google for Dashews / squalls, or get their books - they wrote pretty good stuff on squall 'techniques' - both while chasing and when avoiding them.

barnie
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