Very often she is most noticeable in her endless caprice, by her absence.
More irritatingly than just a day of 'harry flatters' dead calm, when at least you can get on with something else in peace, are days when she arrives all-o'-a-sudden. Or most infuriating of all on the race course, other yachts are in wind and you, poor you, are in a 'hole' or sail into such a place of desparation.
How can we better understand the nature of rapid onset of winds or the occurence of holes?
A Tale of Different Holes
The definition of a hole in the wind would in general be that we see wind other places but find us wind still, or we sail into something which shuts off for a while at least.
Some holes are just that, a patch on the water where there is an abscence of wind. Others are actually not holes at all but bands, and here we get into an explanation of both types.
For a race or cruise then we need to think as we go out of what type of weather we see in front of us, what the forecast says, and how the temperature will vary on land, sea and air through the day due to the effect of the sun, or lack of it. That can inform us as to the likelyhood for holes or bands developing or persisting.
Holes which are bands mark three things:
- There are two winds in different directions that are cancelling each other in a band where they meet.
- That the surface wind is being lifted by convection.
- That there is a seabreeze developing further offshore.
The latter can be a case of the first of the three in fact, more on that later.
What you should do is learn your weather-shift signs, in order to recognise what type of hole you are in, or you can see. Signs such as those nice, hanging cumulus of sea breeze days, thunder anvils in the making, fronts and the calm and windy bands caused sea breeze on the water.
Gradient Wind Days
I never have seen one of those isobars despite a good deal of gazing upon the skies, but our weather forecasters and textbooks tell us they are there. When this so illustrated gradient wind is above 16 knots over land ie flattish coastlines, estuaries and lake areas, then it's effects are often fairly even on the race course, with it tending to go left (anti clockwise, backing) as we near land. Relatively slack wind "Holes" now tend to be places of windshadow, or conversely wind lift, where higher land or buildings cause the verticle wind to reduce.
In lighter isobaric gradient built winds though we have a far more confusing picture. Add to that sailing in lochs or fjords or near long valley systems and it gets more complex. Even a shore side forrest can cause a divergence zone in, and thus a hole which extends some hundreds of meters onto the course you are sailing.
I have actually only heard a few dinghy sailors and otherwise in texts and videos of Olympic briefings about convergence and divergence, but you can bet this theory is one which wiley old sea dogs win races and get home early. It becomes a second sense to the 'empirically' learn-ed who go by years of experience, just knowing that wind along the coast East-West makes for divergence, and convergence West East.
Considering 1 first - Between Two WInds
In gradient wind, we actually have a portion which is usually a 'ridge' between a two low pressures or we are on the edge of where a high pressure's outer ring of clockwise (Northern World) winds are flowing. In the former we can have quite a narrow area in fact because low pressure is establishing itself and eroding the ridge as the pressure gradient builds. But this band is still a good few kilometers, so it is more a general pause between the old and the new gradient wind. Troughs or of course the eye of the storm where pressure is at its lowest are a case of the second.
Another case of between two winds means actually we are where two winds converge and cancel each other out. This is often the case when we have valleys or mountains which split the gradient wind up. Here the effects can be marked even in a lot of wind, depending on how high, or long and what duration it can exert on the wind. You can think of two glacial valleys which train the gradient wind, but then meet over water in nearly opposite directions. Where the mouths meet, and the winds exit the funnel and meet each other, they cancel each other out. This is one reason the infamous "Strone Hole" developes on the old Clyde Championship race course by the Holy Loch. The two lochs are at about 60 degrees to each other, but at the Strone point, they often meet and cancel each other out.
Most often when we are between two winds we are in fact encountering a sea breeze, land convection effect. More on this soon. Also thunder storms draw wind in to them from all edges, and at some place that is of course cancelling out the general gradient breeze out on the fringes of the effect.
2. The Surface Wind is Being Lifted
When the surface wind is lifted it can create a substantial hole, where winds are very light. Again this is dependent on lower wind speeds. In the absence of warm water or solar effect on the land, this can be caused by a nearby high land area to lee of the holes position, which is lifting the gradient wind upwards and creating a hole zone because it hinders the wind ever reaching the surface. The Strone hole above, produces also when the wind is blowing UP the Lochs so I consider this effect to be present, or perhaps the 'suck' of the Lochs makes a dead zone, like the bubble on the foresail luff.
More often though the surface wind is being lifted by a temperature gradient effect, causing verticle convection. This means we have the effects of the sun inevitably unless you are in a volcanic area I haven't heard people sail on. The effects can either be upon the land, nearby if a hole is present, or on the water, or from a waver pattern in the air rolling down with the wind direction.
The latter is the shift pattern in gradient breeze, when we often see small cumulus clouds. The moisture in the atmosphere and the action of the sun means that the clouds are lifting areas and the clear skies to their rear are where the gradient wind and cooler air descends. So we have both more wind and it is usually then veered (N.Hemisphere) to the right, clockwise. As we sail upto and under the cloud we experience a lull and a header on Starboard tack, as we come out behind we experience often a gust and a lift on the same tack. We can use this of course to our position and When the wind is really light but this effect is marked, then we can get holes in the leading edges and under whole clouds.
3. THE SEA BREEZE EFFECTS
This is actually its own little chapter. Sea breeze in the summer, and its own Yan, the night time land breeze, are the greatest friend of those who dare hoist sails aloft. Also it they are a frustrating test of patience especially for those who have long distances to cruise and would rather not rever to motor, or those regatta folk who find they need to wait until 2pm for God to flick the switch, or worse, they find their nice gentle offshore wind replaced by a hole and a 180' wind shift whcih messes up the best of triangular courses.
You can look up the sea breeze yourself, by plenty of the basic videos on youtube and diagrams. However it is fickle when there are complex lands around or when there is gradient breeze in addition.
Remember here that gradient breeze may not mean a low pressure is upon you, it an mean that the centre of the high pressure has moved away and you are experiencing the clock wise winds on its edges. Or the opposite can be true, that low pressure resides but is in a mostly clear zone, with light winds, such that the sun can build up large thermals. Or that either of the 'true' wind's isobaric conditions squeeze over the established/ing sea breeze as the day goes on, in either case of low or high pressure.
Complexities of the Sea Breeze and Its Holey Unholy Effects on the Wat-ter
We have three wonderful sailing areas in the UK which demonstrate admirably the complexities of the sea breeze in our preferred summer months. The Solent, The N.Bay of Cardigan and The East Patch on the Clyde. Also we have a different phenomenon on the west coast and the south coast of Norway as a variance on the case.
Here we see the same phenomenon in the first three places. Local sea breezes can establish themselves if the sea is quite cold relative to the land. Here the sun heats the land from 5am in the morning, and we can get say the Isle of Wight developing a marked sea breeze especially if a new tide has come in and the water is cool. That is on shore pretty much where ever you are around the island. It can take a time to reach the shore in which case you may find a thin, banana shaped band of strangely lonely wind mid solent ( read up about how it reaches into the shore after hitting the water) . Now we have the mainland and this is a much bigger effect due to the south downs getting nicely warmed by lunch time on a sunny day. This means that a sea breeze will also develop there and you may get quite a complex situation where you have in the morning two wind bands at 180 to each other, with a dead zone and occaisionally these two winds kill each other out.
The same is true of the Pwhelli area, where the peninsula makes its own gradient and in fact warms quicker than the shadowy western mountain sides in the morning. On the clyde we have a kind of reverse situation, where the East patch (and most anywhere else) is like a lake thus experiencing winds towards the shore all around it, and dead zones towards the loch entrances.
As the day goes on though, a dominant sea breeze take grip and sucks the air inwards towards the south downs and Hampshire on the Solent, or the mountiains of west wales. The clyde can remain fickle, but usually the centre belt sucks in more than Ayrshire or the North clyde hills.
The sea breeze has a quiet zone in the abscence of higher gradient winds, and that then in the classical conditions shrinks towards the shore until the full effect switches on. The most dramatic I have experienced was about 18 -22 knots which can funneling up the Forth to the Bridges area we were sitting wind-still in the DB2 "Rhett Butler" and it was quite a sight to see the roaring water fill the river and it hit us like a ton of bricks!
In the solent the land mass of Kent often creates a super thermal, and this becomes the most dominant effect so that the wind goes right as the sea breeze builds during the day.
On the south coast of Norway - as a meteorological feature, and sometimes on the W. Coast of Scotland, the 'draw' of the thermals of the sea breeze track westward and northward with the sun's movement over the day as different land areas and mountain ranges heat up. This is because the sun is at a lower angle and the "Kent" or central belt land mass does not happen , the valleys and hills being uneven in their heating inland.
The sea breeze can also spend it's whole day 'off shore' or down the estuary, never filling in, but blowing very merrily out there. THis is where sending someone up the mast can help or using binoculars. On the big year of 'DNF's for the Norwegian 1000 boat regatta, the Færderen Race, we were windstill on the way out near Horten (where the race finished after its traverse down the fjord to Færdern (Tristein) Light) . We noted a mast on the horizon, which through binoculars we could see was the 100 ft Wally being helmed by Knut Frostad. They were well heeled, and that boat cannot be heeled much to lee by her crew. So we percievered and within a couple of hours were into the sea breeze band and enjoying 12-14knts wind, while 700 boats behind us retired and went right into Horten for beers.
Gradient breeze and Sea Breeze- Friends and Foes
The gradient breeze can help or hinder and complicate the picture and is worth a good read with diagrams.
What you can summate though is that direct offshore or slight east to west helps the sea breeze get going, when it is less than about 14 knts forecast. When it is onshore it often hinders the sea breeze. Cross shore will make the sea breeze vector bend towards the direction of travel, it feels like it is more west in an easterly and so on. Convergence and divergence play their parts on how the sea breeze comes to land and where the still bands lie, a diagramatic issue beyond my current tea break capacity I am afraid.
A sea breeze which can then be contrary to an early, light off shore gradient wind. If though a big gradient developes during the day, the sea breeze can be puffed out like a candle. A just-right gradient can also fuel the sea breeze longer into the evening and darkness too. If forecasters say it is not to be very sunny, and there is low pressure, yet it turns out to be sunny and the sea is still quite cold, then you can see a wind at the surface blowing 20 knots to the contrary of a 6 knot wind blowing from 180' the opposite way!
ON DIGGING ONESELF OUT OF HOLES
On a race course we often have the luck of seeing other boats ahead or around us, racing against us or in another fleet or even just cruisers, to act as dozens of little wind vanes. Here we can read where the wind is, and with a little knowledge of phenonmena and a study of the forecast, we can predict both an immediate tactical route to avoid holes, and a wind strategy if we expect more wind to arrive or depart. It can often pay to sail bananas round boats in holes, as I called sailing down the Sound of Mull where 'Defiance' was sitting becalmed in the middle, while there was breeze along the Mull shore. Or it can pay to stay away from a tempting light breeze, especially a local sea breeze to the extreme side of the course if you expect a new wind to settle in, even kedging to hold position and just wait for it to come in such that you end up longer to windward or leeward as required,Out at sea in the N. hemisphere it is an old mariner's saying to haul over to port tack and sit it out, creeping towards the new wind, and that is largely true in the open sea in low pressure because we will either sail into a new wind band or into gradient breeze gradually as the system tracks west to east.
But take a step back here too is that when is a hole actually just very light wind? Get out that cigar or cassette tape band ( an ever rarer commodity now) and see if you need to change gears. Get someone out with binoculars to see if there is wind elsewhere. Often you can percievere through and watch for weather signs underway.
Weather signs are 'tell tale ' in order to recognise what type of hole you are in, or you can see in your way. Signs such as those nice, hanging cumulus of sea breeze days, thunder anvils in the making, fronts and the calm and windy bands caused sea breeze on the water. Look up, think of the temperature in the water and land, look ahead and look all around you.
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