Reading the water surface

[wtarzia]

I was sailing on a calm-ish lake the other week and noticed that, between the ripply areas that signalled a breeze in that direction, there were "roads" of more glassy water. These roads were about 20 feet wide let's say, and went off with minimal meandering for hundreds of feet. If you crossed these roads at right angles more or less, there was some wind (yes, there were large blobs of ripply areas on either side of the roads, so there was going to be wind, but the wind direction seemed to follow the roads, which I thought interesting)

I asked for wisdom from my proa-sailing www buddies and I got lots of it. One guy, a marine biologist, suggested the wind caused upwelling, brining up different water with different surface-tension characteristics, perhaps even biogels. Another guy reminded me the wind likes to curl and spiral as it flows along and perhaps the 'roads' were features from such movements (picture the convergence of twin vortexes and how they affect the water, I guess).

In any event, I am here to ask, if there are some web-sites or publications that deal specifically with reading the surface of the water to guess what is going on with wind, current, chemistry, bottom shape/depth, and tide? Hopefully, with a sailor audience in mind. To be of use it would be a publication with excellent line drawings or photographs. Just wondering. -- Wade

[Tom Hunter]

I went sailing with a glider pilot the other day. Here is his explaination.

He was in Salem, looking across the harbor at a house fire in Marblehead. The smoke went up to a certain height, then blew off in a pattern that looks a lot like waves.

He thinks the same thing happens down at sea level with the breeze. The calm spot is where the peak of the wave of wind has risen up, then the trough hits the water, ect.

I think he may be right. I notice this happens more when the wind is shifting, and in my sailing I am paying more attention to staying in the wind and it is helping the boat I crew place better in races.

[Ian McColgin]

There are many causes of different surface effects on the water. Your description is a perfect rendition of "cat's paws" that come as the air goes from Calm (Beaufort Force 0, if wind, under one knot) to a Light Air (Beaufort Force 1, 1-3 knots wind).

Start by learning the Beaufort scale as it gives both shore based and water cues to estimating wind strength. A picture version helps.

These are purely wind induced waves, quite different in both cause and appearance, from waves caused by current flow, shear effects between different currents, roiling or turbulence of the current over various bottoms, waves from upwelling springs or meeting pelagic currents and so forth.

Additionally, waves are usually the result of several forces. For example, an inlet with a strong ebb will make some nasty steep chop if the breeze is on-shore. Different off-shore conditions each generate their own wave patterns that then meet in combination, leading to the mistaken in detail notion that every seventh (or sixth or whatever) wave is higher.

Any good oceanography primer in your public library will give you a good start at reading water.

[rbgarr]

The calm spot is where the peak of the wave of wind has risen up, then the trough hits the water, ect.

That's what my neighbor, a professor of oceanography says. It's also visible sometimes on tell-tales on the sail: before sailing into a calm streak the telltale settles briefly, sailing out of one it lifts briefly then straightens out more.

[Bill Perkins]

I was pondering this same phenomena from Clay Head on Block Island this Summer .

[wtarzia]

...He was in Salem, looking across the harbor at a house fire in Marblehead. The smoke went up to a certain height, then blew off in a pattern that looks a lot like waves. ...

--- That sounds like Kelvin-Helmholz clouds, which can form where warm air overlies colder air, with a windshear present, so that the boundary between forms "breakers" in the sky. Perhaps it makes sense that this can happen near the water, where friction with the water surface provides the shearing force?

However, if I am not mistaken, the wind on the lake that day tended to flow along the long narrow glassy parts rather than be parallel with it. -- Wade

[wtarzia]

...Any good oceanography primer in your public library will give you a good start at reading water.

--- That was the first thing I did (my college oceanography text) but it didn't have anything except the basics about waves and rouge waves, etc. (As an intro text probably the smaller features of the water surface were too specific...). I just keep thinking someone must have published something for kayakers and sailors. -- Wade

[Milo Christensen]

Sometimes the explanation for the "glassy" streaks is simpler - oil slicks from 2 stroke outboards.

[Bill Perkins]

Milo ; I'd thought the same thing that day on the bluff. I could see the surface well out to sea and there was not a series of such slicks, which seems to undermine the wave theory . The ferryboat route from Point Judith is also just about a half mile offshore ; figured the slick I saw might have drifted in from there.

[DavidF]

I've thought about this an awful lot whilst looking at the surface of my lake. What I have noticed is that these slick areas seem to hang together (same rough shape and size and position for as long as 15 to 30 mintues). If it were caused by shifting wind currents, they would break up and reappear more quickly. They disappear when the wind reaches 5 knots. The lake is very clean and we only use a four stroke (only engine on the lake.) But my guess is that they are oil slicks, natural oils from the environment that want to cling together. This would also explain the slimy foam on the lee shores after a long big blow. I developed this theory reading about how sailors will dump oil to stop the development of white caps.

[Chip-skiff]

There's a type of wind-driven circulation called Langmuir Helices, that occurs with a steady wind (in both speed and direction) right around the speed required to raise waves.

The surface appears to form lanes or streaks, along the wind, often edged with bubbles where deeper water rises to the surface and the gases in solution bubble out.

Here's a diagram from a textbook Limnology by Robert Wetzel, 1983.

http://farm3.static.flickr.com/2434/3846438682_ac363e32bf.jpg

[wtarzia]

No, no motors on this lake. It really seems to appear from the wind. I have tried to notice the same thing when sailing on the coast, but the water around New Haven, CT, is ually too rough. On the doldrums days I think I have noticed this 'roads' and associated flotsam (sea veggie matter) and used to think it was a feature of the tide or other currents, but I am now not sure. -- Wade

[wtarzia]

There's a type of wind-driven circulation called Langmuir Helices, that occurs with a steady wind (in both speed and direction) right around the speed required to raise waves. ...

--- That's it, that's it! Many thanks for taking the time to scan that image and post it. This was interesting.... -- Wade

[Ian McColgin]

The Langmuir phenomenon is a little different from cat's paws, which I grew up reading on Long Island Sound's Long Island side. Cat's paws are the water rippling under intermittant zephers. Anyone who sails such waters much knows them and the good racers know how to stay with one rather than sail out into the inter spaced dead air zones. Cat's paws are not liniar in the same way and often have a slightly globular profile at their leading edge, hense the suggestive name.

[wtarzia]

...Cat's paws are not liniar in the same way and often have a slightly globular profile at their leading edge, hense the suggestive name.

--- Are these the downdrafts off the circulation cells (large cumulus clouds for example)? -- Wade

[rooster]

http://forums.sailinganarchy.com/



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I was sailing on a calm-ish lake the other week and noticed that, between the ripply areas that signalled a breeze in that direction, there were "roads" of more glassy water. These roads were about 20 feet wide let's say, and went off with minimal meandering for hundreds of feet. If you crossed these roads at right angles more or less, there was some wind (yes, there were large blobs of ripply areas on either side of the roads, so there was going to be wind, but the wind direction seemed to follow the roads, which I thought interesting)

I asked for wisdom from my proa-sailing www buddies and I got lots of it. One guy, a marine biologist, suggested the wind caused upwelling, brining up different water with different surface-tension characteristics, perhaps even biogels. Another guy reminded me the wind likes to curl and spiral as it flows along and perhaps the 'roads' were features from such movements (picture the convergence of twin vortexes and how they affect the water, I guess).

In any event, I am here to ask, if there are some web-sites or publications that deal specifically with reading the surface of the water to guess what is going on with wind, current, chemistry, bottom shape/depth, and tide? Hopefully, with a sailor audience in mind. To be of use it would be a publication with excellent line drawings or photographs. Just wondering. -- Wade

[johngsandusky]

There are windrows far out at sea also. I like the explanation of a wind hump. I've had the curious experience of sailing a small boat along on an oily calm sea. It was a melonseed (mast height 10') sailing on LI Sound early spring. My conclusion at the time was that the light breeze didn't disturb the surface of the water because a layer of cold air sat still atop the water.

[Chip-skiff]

First noticed the windstreaks when I was sampling alpine lakes in the Wind River Mountains. There was one long, narrow lake, very deep, that lay along the prevailing wind. With white bubbles on the surface of the near-black water, the lanes were regularly spaced and strikingly well-defined.

I didn't find the name of the phenomenon for a few years, when I took a Limnology class— nice to have one of those Eureka! moments.

[paladin]

The same thing happens at altitude. In a sailplane with electronic thermal sensors you can watch the lift from under one wing pass as a wave right under the plane and pick up the other wing, just reading the lift levels. A neat toy that I borrowed for my Baby Bowlus was an electronic version that used the sensors on the wing, and if you added a couple more, would actually graph the air currents under you, and also noted that the temperature varies in the troughs and crests.