|18th December 2009 10:33 PM|
|vikingsail||There is one other consideration why you may not see whitecaps on photographs or videos. If the photographer is upwind from the sailor the whitecaps are on the backside of the waves; they're hiding. Remember the rule onshore winds rig larger then the water appears, offshore winds rig smaller.|
|18th December 2009 03:47 AM|
Interesting discussion going on here...!
For basic ocean wave formation, please check fluid dynamics theory at http://en.wikipedia.org/wiki/Ocean_surface_wave.
Breaking waves appearing in the form of whitecaps over the sea surface is a wind-driven feature that occurs at a wind speed greater than about 4 m/s (> 8 knots or > 3.5 Bft). Below that wind speed, whitecaps are simply not observed.
Whitecap coverage of sea surface is proportional to both wind duration and fetch.
As wind blows over the sea surface greater than about 4 m/s, a "whitecap" of bubbles and streaks is created on the breaking crest of an ocean surface wave. Whitecaps are formed when large numbers of bubbles produced by a wave rise to the surface, and the bright white area of a whitecap arises from multiple light scattering by elements of size comparable to or greater than the wavelength of visible light. These elements are clusters of proximate, closely packed bubbles at or near the surface of the breaking crest of an ocean surface wave (source http://www.springerlink.com/content/j0647331h845710t/).
So to answer the initial question, yes, it is possible to start and sustain the planing in the absence of clearly visible whitecaps. Formula can do that as of 6-7 knots of wind speed. However, it is impossible to start and sustain the planing as of 4 knots of wind with any type of windsurfing gear, except when the forward motion is provided by the power of a wave pushing the surfing hull down the line.
|17th December 2009 11:52 PM|
Hi Ken, in this one whitecaps are much less noticeable: http://www.youtube.com/watch?v=ugBXkpfHw7o&NR=1
Another factor that may play a role is sunlight. Sometimes you see plenty of whitecaps, then there is a cloud coming and all of a sudden you see much less. (Of course whitecaps are still there, but if this can trick your eyes, it will more surely trick photos or videos). Anyway I remember sunny days with strong offshore wind, certainly more than 10 Knts, and no whitecaps even 100 meters away from the beach. Could very well be that the necessary fetch for 10 Knts to blow whitecaps is several hundred meters, as Carlosgp5 suggests. Anyone with some model?
|17th December 2009 10:15 PM|
I agree that there are several factors that play a roll in developing white caps, but if you look at all the youtube videos on speed sailing, there are plenty of white caps in the speed canals that pop up with only a couple of meters of fetch. The canals are filled with caps. Exactly my point in my first post. Wavelets can cap even if only a few centimeters high.
The video below is an example. While this isn't a canal, it shows how little fetch is necessary for caps to form if there is enough wind. However, I doubt that there would be caps along the shoreline if the wind was 10 knots, but they will form, the only question is how much fetch is necessary to create caps in 10 knots.
|17th December 2009 09:56 PM|
|Unregistered||Like said before (Jean Marc / SKorpio) what you can do in waves breaking on a reef, is slog around the waves to the back of the waves and then use the wave to get planing. Start with leaning forward like surfers do. With hardly any pressure in the sail. You need waves breaking on a reef so you also have a nice quite part which you can use to get out there. In places like Sylt it would be almost impossible.|
|17th December 2009 06:30 PM|
|Farlo||Hi Ken, most probably it can't be related to a single factor (i.e. windspeed). You won't see whitecaps on a speed canal even with 50 Knts blowing. There are no whitecaps when there are no caps (not enough wave height). I guess time, temperature, density, water length & depth... play a role as well.|
|17th December 2009 02:40 AM|
|Ken||After seeing carlosgp5's post, I looked a little deeper. It seems that all the "white cap" formation information on the web is based on the Beaufort scale and they all say that at Force 3 (7-10 knots), white caps begin to form. I don't know if it is at the bottom or top end of the range, but if there is a specific wind speed in knots where caps begin to form, it would be good to know. I have always used the 10 knot rule, but if caps form in less than 10 knots, it would be interesting to know the exact wind speed.|
|17th December 2009 01:04 AM|
From the beaufort scale, from 7 to 10 knots, one should start to see whitecaps...
What I think is that it depends on the distance that the wind is running on the water surface. Lets say, off-shore 10 knots: no whitecaps close to shore, but if you go 1 mile out, youre gonna see them; Now if you have an on-shore of 10 knots, itīll be coming from far of the coast, and there will be a lot of it...
Also, the state of the water will depend on how much time the wind has been blowing for; half an hour of 6 knots on shore, no whitecaps. 6 knots blowing for 2 hours, sure you will see it.
|16th December 2009 07:09 AM|
sorry joe, won't happen again... promise
thanks belskorpio and the guy before, i am fast coming to the conclusion that, unbelievable as it may seem, there are windsurfers out there who are actually more talented than me... a bit of a bombshell...
Your whitecap comments all make sense. A little duckpond can be in 30 knots and have no whitecaps.
On the contrary too, sometimes "Whitecap speak with forked tongue." Sometimes I drive up to a spot, see tons of whitecaps and get ultra aroused instantly, erecting my most manly rig as fast as humanly possible and sprinting into the water. My arousal is quickly deflated when i find myself slogging submarinally at half a knot in wind of about 8 knots... bummer dude...
|16th December 2009 02:53 AM|
I'm just back from Sal, Cabo Verde. I saw Josh Angulo surf in Ponta Preta (you know, the PWA wave spot in february). There was about 12-13 knots of wind, offshore, also bearly no whitecaps. I passed him, fully planing, on slalom equipment ( 115L board + 8.1 rig) just behind huge waves of +3m. He was on wave equipment with a 5.7m rig (yes, that small), schlogging around just behind the waves. Now Josh is quite a bit heavier than me. You should see him when he catches one of those giant waves. I don't understand how he does it. It almost seems that the rig is of no importance anymore. Unbelievable how he rides those waves. I guess he uses all power of the waves. Damn he's good.
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