Understanding Spreckels Lake's Winds -- A Freesailor's Guide to Spreckels Lake
- Category: Member Articles
- Published: Sunday, 11 November 2012 00:43
- Hits: 737
A Freesailor's Guide to Spreckels Lake
by Mike Stobbe
My personal view of Spreckels Lake, its wind patterns, and various geographical zones are shown on the accompanying drawing. I have taken the liberty of making up names for different parts of the lake, which I will refer to below. But first, a disclaimer: Spreckels Lake is notorious for shifty, unpredictable winds. The wind pattern I have drawn represents only my opinion of a generalized condition, based on ten years of personal experience. On any given day (or hour) the actual wind pattern may vary widely from that shown. Again, this is my own view. Others may hold a different opinion. Spreckels Lake is anything but consistent, and doesn't readily yield its secrets. In the drawing, the lengths of the arrows are intended to represent relative wind strength. The lake perimeter and outline of the tree growth is traced from a Google airphoto. It's quite accurate.
The normal wind direction at San Francisco is from the northwest. Down at the ground level in Golden Gate Park, however, the presence of trees and open spaces conspire to wreak havoc on the steady and consistent wind over the ocean, only a mile away. The winds at Spreckels Lake typically come in through two widely spaced gaps in the trees, join forces in mid-lake, and exit through a narrow corridor to the east. The dominant gap is at the northwest corner of the lake, and is responsible for what is known as the Street Breeze, referring to Fulton Street. Fulton Street is a wide, straight corridor running due west right to the beach; an unimpeded route for the ocean breeze. A gap in the trees where 36th Avenue enters the park tips the breeze directly onto Spreckels Lake. The second wind gap is located at the center of the lake's south shore. I refer to this wind as the Rhododendron Breeze, as it comes in directly over Rhododendron Island in JFK Drive. It's not really clear to me how the wind comes in here, because it's usually at about 90 degrees to the regional wind direction. But there's no doubt that it does. The Rhododendron Breeze has a strong influence on the Street Breeze, striking it at right angles in the middle of the lake. This collision of winds defines the general pattern on Spreckels Lake, but the actual pattern at any given day or moment will depend upon the relative strength of the Street Breeze compared to the Rhododendron Breeze.
In the drawing, the breezes are shown meeting head-on east of Punto Blanco, in an area I call the Sargasso Sea. The opposing winds cancel each other, creating a "dead zone." Further east, the two breezes join forces and turn east. The line demarcating the Northern Trades and the Southern Trades is an extension of this "dead zone". In point of fact, however, this line, running roughly east-west from Punto Blanco to the Roaring Forties, is constantly being pushed further north or further south depending on the relative strengths of the Street Breeze and Rhododendron Breeze. When the Street Breeze dominates, it may push all the way to the Forbidden Coast. When the Rhododendron Breeze dominates, it often will reach the north side of the lake. It is this endless shoving match that makes the wind on Spreckels Lake so unpredictable.
Further east, the narrowing shape of the lake, together with the trees on either side, tends to funnel the wind, concentrating it. Here, in what I call the Roaring Forties, are found the strongest winds on the lake. Freesailers start and finish at the northeast and northwest corners of the lake. Thus the preferred route is to keep close to the north shore. This is the reason I refer to the Street Breeze as being the dominant breeze. The influence of the Rhododendron Breeze is important to understand, but if you want to win, you'll want to stay in the Street Breeze. SFMYC freesailors begin their racing boards with the run, and finish with the beat. Thus I will begin describing the individual features and areas with Heartbreak Harbor.
Heartbreak Harbor, the start of the freesail run, is the scene of the most perfidious winds known on the planet. As shown by the wind arrows, upon passing the gap, the southern portion of the Street Breeze curls around to the south and becomes much weakened as it spreads out into the available area. What is not shown, is the most diabolical feature of Heartbreak Harbor, and the source of its name. There is a higher-level west wind passing over Golden Gate Park above the trees. As this wind clears the trees west of the lake, localized transient downdrafts penetrate the Street Breeze and come down to the water. When they strike the water, these downdraft bursts spread out in all directions. A downdraft directly in front of you will curl back to blow a starting boat back to the shore, while on either side these downdrafts turn north and south. These adverse winds usually last 15 to 30 seconds, but occur every minute or less. Skippers cannot anticipate these downdrafts, since the west wind is passing high over their heads and the downdrafts strike the water just offshore. It often takes more than one try to get out of Heartbreak Harbor, and it is common to see boats side by side go in opposite directions. Winds are typically light to very light, even on windy days.
The zone of these downdraft bursts, which have broken so many hearts, doesn't ordinarily extend beyond the limit shown for Heartbreak Harbor. Thus, if you've made it as far as Point Eureka (hooray!) you can count on not being blown back to the starting line. Point Eureka is marked by a large cypress tree near the water's edge. This cypress tree also casts a wind shadow, Deception Pass, which is usually only a minor inconvenience but on occasion has been known to turn back a beating yacht into a 360 degree turn.
The Sargasso Sea is a large extended zone of light and shifty winds, often with calm spots. It is caused, in part, by the wind shadow of trees behind Punto Blanco (White Point), but primarily by the collision of the Street Breeze and Rhododendron Breeze as described earlier. The southern curl of the Street Breeze often carries running boats into the Sargasso Sea, where the race is usually lost while they eventually muddle out of it. Punto Blanco is so named for the generous layer of bird guano found there. A place to be avoided!
Running boats not carried into the Sargasso Sea will find themselves in the Northern Trades. This is the ideal place to be, truly the Spreckels "sweet spot", if I can be excused the pun. Winds here are relatively steady and reliable by Spreckels standards (i.e. not very). If you are running close to the north shore, as is usual, note that the influence of the Rhododendron Breeze bends the wind direction to the north, sometimes more strongly than is illustrated. This will cause your boat to crowd the shore, requiring steering adjustments to hold it off. As one proceeds eastward, the effect becomes greater, requiring further steering adjustments. Until, that is, you reach Point Sayonara, which is the point at which you can kiss your boat goodbye!
Point Sayonara is that point where the wind usually takes a more westerly direction, as well as becomes stronger. You will suddenly find yourself overcorrected, and instead of crowding the north shore, your boat will suddenly veer south, heading for certain shipwreck on the dreaded Skeleton Coast. You have left the Northern Trades and have entered the Roaring Forties. On windy days, boats often broach here, especially if they are Braine-controlled. At every regatta, freesail skippers are observed breaking into a run at Point Sayonara in a desperate bid to reach the Skeleton Coast before their boat wrecks there. They are usually puffing hard by the time they round Cardiac Cove, hence its name. A boat striking the Skeleton Coast invariably swings around to point west, thereby failing to finish the run until its skipper arrives, clutching his chest.
On the run, boats that have been set too far to the south or have passed through the Sargasso Sea may find themselves in the Southern Trades. The winds here are generally quite good, however since the vane was ordinarily set in anticipation of being in the Northern Trades, boats usually track across the Southern Trades to a lonely shipwreck on the Forbidden Coast. This stretch is too remote for any skipper to reach in time and the bumper boards bear the faint impressions of innumerable past wrecks. Even if the boat tracks northerly enough to just skim past Last Chance Point, by now you will have sailed so far from your proper course that your race is almost certainly lost.
When one considers how the narrowing shape of the lake concentrates the wind in the Roaring Forties, you may be forgiven for thinking that it must be a veritable hurricane in Cardiac Cove. However, this is not usually the case. To be sure, on very windy days, it can blow hard in Cardiac Cove. But on light or moderate days, the wind strength here falls off markedly. This is because the trees surrounding the east end of the lake force the wind to rise up, lifting off the water and leaving light swirling eddies below. Wisely, the eastern start-finish line is, for the most part, located west of this effect.
The return beat starts at the north end of the line. Compared to the numerous opportunities for disaster on the run, the freesail beat at Spreckels Lake is a cakewalk. Right out of the gate, if you find that your boat hasn't been set up to tack properly, you will wreck on the Skeleton Coast. Unlike the run, however, as the hull swings around to the west it will be pointing in the right direction and, with luck, your boat will complete a "bounce-tack" and be on its way. It may stay "pinned" to the shore for a while, but it's no good running around Cardiac Cove because the boat will always break free and be gone just before you reach it. How it knows to do this, is a mystery.
Most of the time, the beat is straightforward and uneventful. But bear in mind that the wind becomes lighter and more fitful as one approaches Point Eureka. Many a straggler has caught up to the leader in the last few feet to the finish line. As we say here, "It ain't over 'til it's over!" However, there are two general conditions that can cause trouble on the beat: when the regional wind is more northerly than usual, and when it's more southerly than usual.
When the wind is more northerly than usual, the Street Breeze can drive all the way to the Forbidden Coast, pinching off the Rhododendron Breeze. It will also squeeze out between the trees along the north shore in discrete localized vortices. If you've just poled your boat out for a starboard tack when one of these bursts occurs, you may suddenly find the wind directly behind you and your boat may do a close-hauled jibe and circle around for a 360-degree diversion. This risk is greatest between the starting point and Point Sayonara. Also, with a northerly wind, your boat may crowd the shore on a starboard tack. Under these conditions, if your boat is equipped for it, you may try to set it up for asymmetrical tacking: close-hauled on the port tack, and somewhat looser on the starboard tack. The risk, of course, is that wind conditions are so changeable at Spreckels, that by the time you've made the adjustments, the wind has swung back to westerly again. One last item: when the wind is more northerly than usual, the wind shadow thrown by the big cypress at Point Eureka will be angled further out into the lake, making the Deception Pass zone much larger. Here also, beating boats sometimes get turned back for a big 360-degree detour.
When the wind is more southerly than usual, the Street Breeze is squeezed closer to the north shore. Under ideal conditions, the beat is conducted entirely within the zone of the Street Breeze. With a strong southerly, the Rhododendron Breeze may come so close to the north shore that boats on the starboard tack can venture into it before turning back onto the port tack. When this happens, a beating boat may be unwillingly lifted too far south on the port tack. Where it ends up depends largely on where it entered the Rhododendron Breeze and how southerly the wind direction is. If it entered near the starting line, it will very likely be carried all the way into Motor Boat Bay, the haunt of the Power Squadron. There is no exit from Motor Boat Bay. One must make the long trudge, pick up the boat, and carry it to the finish area. If the boat enters the Rhododendron Breeze nearer to Point Sayonara, it is more likely to be carried into the Sargasso Sea. Here, the winds are lighter, and very unpredictable, very shifty. With luck, the boat may be deflected back into the Street Breeze for a successful finish. Equally likely, the boat may eventually fumble into the Bermuda Triangle or Turtle Bay. Tall eucalyptus trees to the south create a very pronounced wind shadow here. The Rhododendron Breeze curls westward around these trees in a pattern of transient gentle vortices with no clear direction. Although not triangle-shaped, the Bermuda Triangle shares one feature with its more famous Floridian namesake: boats entering here are never heard from again. Past Clubhouse Point lies Turtle Bay, so named for the large decorative concrete turtle found there. If by some miracle your boat manages to make it this far, it may actually finish. It will be a pyrrhic crossing, however, for your competitors will probably have already gone home by then. Turtle Bay never has wind, none, ever, nada.
If, on a day with the wind more southerly than usual, you've managed to keep to the north side and stay in the Street Breeze beyond Point Sayonara, then you'll likely stay in it to the finish. The risk of being lifted to the south shore originates almost entirely between the start of the beat and Point Sayonara. To guard against it, you can try setting your tacking angles asymmetrically, as described earlier for a northerly wind, but this time easing the sheets for the port tack.
I hope you will find this description of Spreckels Lake wind conditions useful. If I've made freesailing on Spreckels Lake sound like a grim proposition, take my advice: lower your expectations, enjoy the day, and find satisfaction in challenging what must be one of the most difficult lakes in the world to sail on. After all, you wouldn't want it to be ho-hum, steady and consistent every day, would you?