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Old 17-03-2011, 07:42   #16
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Re: Clearance under keel for hurricane anchoring?

Hurricanes "suck" literally. As a massive low pressure system they suck surrounding water for form their surge dome. So you can expect the waters around your boat to depart just prior to the storm's arrival and be followed by an dramatic return of the water and more with the storm. I was in Miami a couple of decades ago for Hurricane Andrew which pretty much sucked Biscayne Bay dry - 14 ft - and then the surge brought it all back in plus another 10 to 14 ft which put boats up on top of marina pilings and up on inland roads. A tiger shark was found 1/4 mile inland up on a guy's front porch flopping around.
- - Here is an except from a public NOAA paper on Storm Surge:
Storm surge is a great dome of water often 50 miles wide, that comes sweeping
across the coastline near the area where the eye of the hurricane makes landfall. The
surge, aided by the hammering effect of breaking waves, acts like a giant bulldozer
sweeping everything in its path. The stronger the hurricane, the higher the storm surge will
be. This is unquestionably the most dangerous part of a hurricane. Nine out of ten
hurricane fatalities are caused by the storm surge. During the infamous Hurricane Camille in 1969,
a 25-foot storm surge inundated Pass Christian in Mississippi. Lesser height are more usual but
still extremely dangerous.


- - So unless your boat can rest on the mud bottom without falling over - you need significant water under your keel and an awful lot of anchor rode out to handle the water rise due to the storm surge.
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Old 17-03-2011, 08:04   #17
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Re: Clearance under keel for hurricane anchoring?

I weathered Ike, (class 4), with a storm surge of 20ft. I went inland into a canal that had depths of 5 ft under keel, (it was protected from waves), and was surounded by high rises, (protected from wind). And tied off with 30 ft lines, (20 foot slack). The water reached the second floor of the high rises, and an observer stated my lines were fully stretched. Out of 16 lines, two broke. The boat came through without a scratch except the screens were peeled off of the windows. All of the boats that were tied up like mine survived. The others were sunk or sustained major damage, (IE ending up in the street or someones back yard). There is a marina in my area called Watergate that is surrounded by a high concrete wall, and floating docks. Many boats survived there also.

Moral
Find a protected spot away from the hurricane winds, (they may come from two sides if the eye passes over). Prepare for the projected storm surge, with many lines arrainged for maximum slack. strip the boat, you may never see it again. Remove ALL canvas, (and screens). Try to locate your boat away from the main force of the storm, if possible. Help your neighbors to tie up, many boats were sunk when other boats tore loose and rammed them. At least two lines on every cleat, with snubbers. The lines all had stretches, and wear abrasion spots in spite of my best efforts to put on chaff protection. Debris and flying sharp objects cut several lines. Good luck. (luck favors the prepaired).
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Old 17-03-2011, 08:11   #18
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Re: Clearance under keel for hurricane anchoring?

In a hurricane/tropical storm water levels change very quickly as the storm passes. Two years ago I stayed aboard for a tropical storm. I normally have about 2 feet of water under my keel in my slip. This was only a 60 MPH storm, but the water came up about 3.5 feet as the storm approached. As the eye passed the wind changed direction and 45 minutes later I was sitting on my keels. The water was going out so fast there were 6 inch wakes coming off of the pilings. In a really strong storm I would plan on the possibility of sitting on the bottom even in relatively deep water as well as planning for very high surge. The key is getting some place without much exposure to fetch so you oly have to deal with wind and current, not waves. Getting bounced on the bottom in wave troughs will destroy most any boat.
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Old 17-03-2011, 10:19   #19
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Re: Clearance under keel for hurricane anchoring?

Quote:
Originally Posted by capngeo View Post
A home built big ol' honking anchor... We're loaded with them in KW
Haha, well said.

Thanks.
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Old 17-03-2011, 11:18   #20
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Re: Clearance under keel for hurricane anchoring?

After you allow for the lowest tide then deduct whatever you expect the waves to be and a margin. There is the surge so I bet there is the counter-surge of sorts too.

If you cannot go into deep water, which would be my preference, at least try to find out where the bottom is mud rather than compacted sand or reef. Just in case you do touch.

b.
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Old 18-03-2011, 08:49   #21
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Re: Clearance under keel for hurricane anchoring?

A shrimp boat anchor goes by the name Northill, usually hand built and about 200 to 300 pounds, and you need a winch to use it. If you're in Key West, I would consider coming over to Stock Island and hauling out for a real storm, cost you about $15 a foot and you can knock out a bottom job at the same time. At the end of the day you will still have a boat.
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