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Old 24-01-2009, 05:07   #1
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Would You Cross the Gulf Stream?

I keep checking the weather for areas that we'll be traveling in six weeks or so and trying to decide on good weather windows...just an exercise to help me learn.
Now, here are today's conditions for the area east of Palm beach:
NORTH WINDS 5 TO 10 KNOTS. SEAS 2 TO 4 FEET. INTRACOASTAL
WATERS A LIGHT CHOP. SLIGHT CHANCE OF SHOWERS.
With a North wind, even a light one like this wouldn't you expect the Gulf Stream to be pretty choppy and disorganized?

And what about the conditions predicted for Monday:
NORTHEAST WINDS 5 TO 10 KNOTS BECOMING 10 TO
15 KNOTS. SEAS 2 TO 3 FEET. INTRACOASTAL WATERS A MODERATE CHOP.
SLIGHT CHANCE OF LIGHT SHOWERS.

With the northerly component is the Gulf Stream likely to be pretty uncomfortable? On the other hand, a completely easterly wind would mean motorsailing the whole way.

I'd love to hear any comments from people who've made that crossing a bunch of times.

Bill
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Old 24-01-2009, 05:26   #2
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At the sailing school / charter company I worked for in Ft. Lauderdale back in the 80's, the rule of thumb was 15 knots maximum from a northerly direction (nw, n, ne). At 15 knots from the NE, you'll be beating into maybe 6 footers, steep 6 footers, not very comfortable. With wind from the NW it will be a little more comfortable. Also, when they say 2 to 4 feet, if you add the numbers together it will probably be closer to the actual wave height.
What happens if the the forecast wind speed is a little on the low side? a very uncomfortable ride!
Brian
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Old 24-01-2009, 05:50   #3
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When crossing from South Florida, changing winds will “clock” as low pressure systems pass to the North of you. Accordingly, you can generally expect winds to vary from NW to N to NE to E to S to SW, and finally to W, with time.
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Old 24-01-2009, 05:54   #4
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Have you visited PassageWeather? PassageWeather - Wind, Wave and Weather Forecasts for Sailors and Adventurers Click your way in on the maps till you get the close-up of Florida and the Bahamas. Then if you click "Next," it'll give you predictions for wind direction, force, wave height, etc. in 12-hour increments looking out a week or so. Usually a norther will clock around and blow from the east, then south after a few days. (I've never made the crossing, so I can't comment on your real question of "Would you cross in these conditions?" But I've been planning a Bahamas trip for a while now, and I love to play the same game -- watching the weather from afar, and contemplating when to go. . . .)
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Old 28-01-2009, 13:51   #5
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My wife and I have been crossing to and from the Bahamas since 1975. We often wait for a nice weather opportunity from Lake Worth Inlet to head for the Bank just south of Memory Rock, but if there's winds up to 15 from the north we'll cruise down to Lauderdale and ride with the 'stream up to West End after the winds have clocked. We don't favor big bucks at marinas, so if we end up in Lauderadale we will take a Las Olas mooring, one night anchor in the little lake south of Bahia Mar or a $50 dollar slip for a night up the New River at Cooley's Landing. 'take care and joy,
Aythya crew
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Old 28-01-2009, 16:28   #6
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correct me if I'm wrong but 3-4 ft seas are 6-8 trough to crest.....
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Old 28-01-2009, 17:20   #7
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Quote:
Originally Posted by Cheechako View Post
correct me if I'm wrong but 3-4 ft seas are 6-8 trough to crest.....
Absolutely, its measured from the 'level'.
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Old 28-01-2009, 18:30   #8
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There's a big difference between Florida 3-4 and North Carolina 3-4. In Florida it seems to be measured from trough to crest. In the Pacific, 3-4 is a flat calm.

A factor easily as large as the GS factor is coming up on the shelf--shallow water is bad.
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Old 28-01-2009, 20:57   #9
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Winds are hardly ever good for going over, most always good for coming back. Over 15kts don't go over, . 3/5' seas are same everywhere, even in your bathtub.
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Old 28-01-2009, 20:59   #10
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correct me if I'm wrong but 3-4 ft seas are 6-8 trough to crest.....
nope, try again
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Old 28-01-2009, 21:12   #11
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Winds are hardly ever good for going over, most always good for coming back. Over 15kts don't go over, . 3/5' seas are same everywhere, even in your bathtub.
You know, I'm gonna have to go ahead and disagree with you. I've been in 3 to 5 mid-Atlantic, and it was a breeze. Been in 3 to 5 in the Chesapeake, and almost had my boat rolled out from under me. Have you spent much time at sea? Current changes EVERYTHING...
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Old 28-01-2009, 23:46   #12
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You know, I'm gonna have to go ahead and disagree with you. I've been in 3 to 5 mid-Atlantic, and it was a breeze. Been in 3 to 5 in the Chesapeake, and almost had my boat rolled out from under me. Have you spent much time at sea? Current changes EVERYTHING...
only 40 yrs. Chesapeake" 3/5' is more of a chop. One of the hardest crossings I remember was a 8/10' in the Rebecca Shoal area between Marquesa's and Dry Tortugas. Tropical Storm Claudia, winds had whipped up the channel for 4 days. It was a straight up and straight down, close chop, mean, against the current. I considered myself lucky to live through it. Compares to 30 to 40' in the North Atlantic. Yes, there are many different conditions out there but still measued in feet and a foot is 12" everywhere
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Old 29-01-2009, 03:55   #13
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There are two attributes used to measure open ocean waves: Height (amplitude) and Period (frequency).

Wave height is the distance from a wave's trough to its crest (i.e. amplitude). The crest is the top of an unbroken wave, the trough is at the bottom of the front of the wave.

Some Hawaiian surfers measure the back, rather than the face, of a breaking wave.

Wave period (or wavelength) is the amount of time (in seconds) it takes from the moment one wave crest passes a fixed point until a second wave crest passes that same point.

Typically one will hear waves described like, " It's 5 ft @ 13 seconds". What this means is that the average height of the largest 33% of the waves are 5 ft and that the average period (time between wave crests) of the most prevalent swell is 13 seconds.

The ratio of wave height to wavelength gives the wave steepness. Water depth determines whether we have a deepwater wave or a shallow water wave.

Wave height measurements come in two flavors: Significant Seas and Swell.

"Seas" are the combined sum of the heights of all waves present at the reporting station. Think of it as the average wave size. For example, it there is a 5 ft swell coming from the north, and a 3 ft swell coming from the south, it would be reported as a 6 ft sea. ('Seas' are actually the square root of the sum of the squares of all wave energy present).

Swell height is the 'average' height of the highest 1/3 of the most energetic swells present at that reporting station (a buoy). Swell period is the average period of the most energetic swells.

If you're in or near a major fetch area (a storm), waves of different heights and period momentarily combine as they pass through each other to form larger waves. It makes no difference whether it's chop or swell. On average, about 15% of waves will equal or exceed the significant wave height. The highest 10% of waves could be 25-30% higher than the significant wave height. And on occasion (about one per hour) one can expect to see a wave nearly twice the significant wave height.

You can over estimate, or you can under estimate wave heights.

CORRECTION:
Quote:
Originally Posted by GordMay
There are two attributes used to measure open ocean waves: Height (amplitude) and Period (frequency).

Wave height is the distance from a wave's trough to its crest (i.e. amplitude). The crest is the top of an unbroken wave, the trough is at the bottom of the front of the wave...
bene505 pointed out, in a PM, that my use of the word amplitude, to describe a trough to crest (positive + negative displacement) wave height was imprecise and misleading.

The term amplitude can have slightly different meanings, depending upon the context of the situation, and modifying prefixes and words.

It’s most general definition, however, is that the amplitude is the maximum positive displacement from the undisturbed position (sea level) of the medium (water) to the top of a crest, or it’s maximum deviation from the average or equilibrium value. This would be only one-half the trough to crest value that I was describing.

When dealing with alternating current electrical power, it is common to specify RMS* values of a sinusoidal waveform.
* RMS (Root Mean Square) is defined as the square root of the mean over time, of the square of the vertical distance of the graph, from the resting state (such as ground or 0V).
RMS voltage = 0.707 Peak Voltage
Peak Voltage = 1.414 RMS voltage

There are also other “special” amplitudes.

I apologise for any confusion my misuse of the term may have engendered.
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Old 29-01-2009, 04:06   #14
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If this is your first Gulfstream crossing, you do NOT want to go in any variation of a north wind, nor the day after to give the 'stream time to calm down. Gord is absolutely right about the winds clocking, and it is well worth the wait to have a lovely sail in s or sw winds to the Bahamas instead of pounding into large seas that build in the Gulfstream when the winds are blowing from the north and the stream is running up from the south.
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Old 29-01-2009, 04:52   #15
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Most sailors know that waves "pile up" in shallow waters, that longer fetch allows larger waves and a longer winds add to the "magnitude" of waves.

I've sailed when the winds were quite strong in the bay after a long calm - hardly any seas running and the boat sails like a bat outta hell. And the reverse is hell, the winds die and the sea is still steep and confused and you can barely make way (whereas in flat seas you'd be sailing quite nicely. We all be there.

I would like to learn about the dynamics of waves in different depths. Here are some of my "theory questions":

How DOES the wind actually create waves?

How is sea depth actually "seen" by the surface waves?

What is the relationship to sea depth and height of waves? For example can 15' of water see 6' waves? 8'

How does shallow depth cause waves to crest and overfall? Is this the result of the bottom coming up fast?

Are all waves the same shape / profile in very deep water or is do their characteristic change at they get larger?

What makes waves of the same height have different "periods" from crest to crest?

Why don't steady winds continue to increase the size of waves? I realize that there is a limiting factor?

Does air temperature have an impact on wave making? Does humidity?

How do rain drops calm waves? Doesn't this seem as a tiny force compared to that of the waves?

Are salt water waves different from fresh water?

Are warm water waves different from cold water?

How does an oil slick actually prevent waves from breaking?

Explain waves
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