The Stobbe Vane: Tacking Upwind with the Self-Steering Vane by Mike Stobbe

The Stobbe Vane: Tacking Upwind with the Self-Steering Vane By Mike Stobbe

In the previous article, I described how the vanes built by Jeff Stobbe should be prepared for use. Sailing with the self-tacking vane is relatively straightforward. Much of it comes down to careful preparation beforehand. Many thanks to Drew Marshall for his review and helpful comments contributing to this article. It is assumed that the boat has already been dynamically balanced with respect to the mast position and jib pivot position. If the boat is well balanced to windward, it will pretty much sail itself, and the vane will have a very light duty to perform. A "problem" with vane-controlled boats is that even a mediocre vane setting will enable a boat to beat so relatively well, that many skippers are content to leave it at that and not bother to seek the most out of it.

You are now ready to go sailing. This article is not about rigging or the setting of the sails, however, it's worth mentioning to the reader that for good upwind performance, the rigging should be set to ensure that the jibstay is really taut. Set the vane onto the vane post, and engage the operating pin with the tiller slot. Clip on the safety line. Tacking upwind (beating) with a self-steering vane is quite simple. With the vane locked, rotate the vane body until it is pointed exactly straight ahead, with the feather right aft. The correct way to do this, is to rotate the vane until the operating pin is hard up against the end of the tiller slot, and then to continue rotating, against the friction grip of the clamp-screw, until the vane body aligns with the straight-ahead mark obtained from the degree-board. The incorrect way to do this, is to grasp the rudder blade, and rotate the vane while holding tiller in the straight-ahead position. The latter method will torque the tiller's clamping block on the rudder post. It may slip, unnoticed until you release the boat…too late! The correct method puts no stress on the rudder post or the construction joint between the rudder post and rudder blade. The vane must be locked to make this straight-ahead setting. After the vane is set to the straight-ahead position, use the beaded chain to set the rudder-centering elastic to a very weak tension, just enough to keep the beaded chain from dragging on the deck. If the boat is equipped with a slotted comb, set the beaded chain on- center. No rudder offset is used when beating. Note that the centering elastic not only returns the tiller to center, it also offers resistance to the vane rotation. When beating, we want the former, but not the latter. Thus, we want as little tension on the centering elastic as will still do the job. Now unlock the vane. Ensure that the gying spring is hooked on the side of the feather bracket that is nearest to the shore that you will be walking on. At Spreckels Lake, the prevailing wind and shape of the lake dictate beating westward, walking along the north shore. Thus the gying spring will always be attached to the starboard side. If you wanted to sail a windward board walking along the south shore, you would clip the spring to the port side of the feather.

1 With the sheets set in their beating positions, place the boat into the water, pointing into the wind. Holding it by the stern, allow it to pay off until the sails just fill and stop luffing. As the boat begins to heel over to the wind, let it go, and closely observe its progress. Potential adjustments will be to the gying spring tension and the tacking angle.

The tension in the gying spring should be fine-tuned each day that the boat is used. Take note of how the quickly the boat tacks upon release or turn-out with the pole. If it consistently tries to tack immediately, within one or two boat-lengths from shore, then the gying spring is too tight. If it goes all the way across the lake without tacking at all (apart from induced tacks caused by large wind shifts), then the gying spring is too loose. The difference between too loose and too tight is very slight, however. This is a very sensitive adjustment. Make gying spring adjustments of only about ¼" or less, by sliding the transverse adjusting hook on the feather bracket. Observe the boat to gauge its effect before adjusting again. The initial setting should prove to be very close. However, in general, windier days require a bit more tension, and lighter days a bit less tension. Also, be aware that for the vane to flop over, the boat must come upright at least momentarily, due to a lull in the wind or being headed by a wind shift. On Spreckels Lake one can always count on this, but if sailing elsewhere under strong and steady wind, the boat may stay heeled over on its initial tack for a long time; the vane unable to flip over due to the steady wind pressure on the vane feather. In such conditions, the gying spring will need significantly more tension. For the same reason, the boat should be turned out far enough for the sails to fully fill. The boat needs to be heeling a bit as it leaves the shore to ensure that the feather droops to leeward. If it leaves the shore with the feather still flipped to windward (i.e. in the same position it was in when it approached the shore on the other tack), then the boat will immediately try to tack, and will probably fail because it will not have gained enough momentum (known as "way") to complete the tack. Failure to tack is more fully discussed at the end of this article. As mentioned at the beginning of this article, a really well-balanced boat will sail itself, going to windward. A clear advantage of vane control, however, is a faster response to being headed. With or without a vane, a well-balanced yacht will naturally rise to a lift. A headed yacht without a vane, however, will begin luffing, slow down, gradually pay off until the sails fill again, and then gather speed on the new course. A well set-up vane-controlled boat, by contrast, should quickly steer to the new course when headed, with only a brief moment of luffing, provided that the skipper has the correct relationship between the slack gying spring tension and the tiller-centering elastic tension. Upon consideration, one will realize that this relationship also plays a role in a vane-controlled boat's ability to complete a tack, as tacking is essentially a continuation of the response to being headed.

After a little practice, you will soon become familiar with the effects of the gying spring tension. Once you're experienced enough to be confident of the effects of adjustments to the gying spring, you may even try using it as a racing tactic. Two scenarios are likely possibilities during a race. In the first case, shown on Figure 14, one is nearing the last tack of a windward board on a lake where the wind direction is far from perpendicular to the finish line. Under such conditions, one end of the line will be favored over the other, and a shorter sailing distance will be required to reach the favored end. Note, as depicted on Figure 14, that if two boats leave Point "B" the skipper who increases his gying spring tension to

2 force a short tack, may reach the finish line at Point "C". The skipper who continues with a gying spring having a low tension, makes a long tack, and is shown reaching the finish line at Point "D". The second skipper will only have reached Point "D' " when the first skipper finishes.

Figure 14. Short Tack vs. Long Tack to the Finish Line

Figure 15. Short Tack vs. Long Tack for the Best Wind

The second scenario involves using the gying spring tension to induce a long tack or a short tack to avoid known wind shadows caused by trees, or to stay as much as possible in areas of the lake known to have the best winds. An example is shown on Figure 15. A word of caution, however. On a lake with very shifty and unsteady wind such as Spreckels Lake, the distance a boat will travel before self-tacking is very uncertain. One must weigh the risk of wasting the time for a change of trim for the purpose of taking advantage of what may be a very fleeting wind condition, against a benefit that may or may not be realized.

The vane tacking angle must also be fine-tuned, but once set, will not need to be adjusted very often. Once you are satisfied with the tacking angle, you can leave this adjustment alone much of the time. The final tacking angle is dependent upon many factors; some are under the skipper's control, and some are built in to the hull design and cut of the sails. Notice I don't refer to the "correct" tacking angle. There is no "correct" tacking angle. There is only the tacking angle best suited to your boat and the way you like to sail it. Good windward work depends entirely upon sail trim. The angle at which a boat sails into the wind will vary with the trim of the sails. To make her point higher, you pull the sails in a little closer. This will require a smaller tacking angle setting on the vane. The general principal is that the narrower the boat's tacking angle relative to the wind direction (i.e. the closer you "point" to the wind), the shorter the distance the boat will have to travel to get up the lake. At the same time, the closer you point to the wind, the slower the boat will go. With a wider tacking angle, the boat will go faster, but it will have to travel farther, perhaps requiring an extra tack to reach the finish line. It's a trade-off between "pointing" and "footing", which depends, in part on the personal preferences of the skipper and the shape of the hull. A boat's tacking angle, for a given hull shape and sail camber, will be determined by the angle of the main boom and jib boom to the centerline of the boat. Generally speaking, deep, narrow, vee-shaped hulls can carry their booms closer to the centerline than can wider flat-bottomed hulls. The optimum boom angles needed to make your boat point its best while still moving fast can only be found through experience. The important point to remember is, that regardless of the boom angles used, the tacking angle set on the vane must be in harmony with the actual angle of boat's course relative to the apparent wind. A vane set to a wider tacking angle must correspond to an easing of the sheets to give a wider boom angle. A narrower tacking angle on the vane must be used in conjunction with a narrower boom angle. If there is a significant discrepancy between the vane setting and the boom setting, the yacht will naturally try to point as a result of the sail trim, and the vane will be continually working to force it to sail higher or lower as the case may be. The persistent helm imparted by the vane will slow the boat down and cause an erratic course.

Set your main and jib sheets where you want them (as determined during dynamic balancing), and the vane tacking angle at the initial setting previously recommended. Generally, a vane-controlled boat should be set with the mainsail sheeted in a few degrees closer than the jib. Send the boat off and observe the forward edges of the sails, the luffs, as the boat sails. Be sure to observe the boat on both tacks. If the luffs start fluttering, especially the jib luff, then you are trying to point too high. If you are pointing too low, the sails remain full and there is no visual indication that the boat is sailing below its potential. In this case, it is useful to tape colored pieces of yarn, called tell-tales, to each side of the sail to provide a visual indicator of the airflow along the sailcloth. Tape a piece of red yarn on the port side and, a couple of inches lower, a green yarn on the starboard side, near the jibstay, streaming aft. When pointing correctly, both yarns will point straight back. If pointing too low, (i.e. away from the wind), the leeward yarn will hang straight down. Laminar flow has been lost, and the air moving over the sail has become turbulent. The condition is comparable to an airplane wing stalling.

Figure 16 Setting the Tacking Angle

If the boat is trying to point too high, widen the tacking angle one degree at a time until the luffs stop fluttering (one revolution of the large washers, Figure 16). If pointing too low (the leeward yarn hangs down), tighten up the tacking angle one degree at a time. Adjust both sides equally. When the sails neither flutter nor the yarns droop, this will be the best tacking angle for that boom position, but at the beginning of each windward board, the booms should be consistently sheeted in to the same spot. If the mainsail begins luffing before the jib does, the mainsail is being backwinded by the jib. Try to correct this by sail adjustment before changing the vane setting. Either a.) ease the jib sheet and/or tighten the mainsheet, or b.) ease the leech tension on the jib and/or flatten the mainsail's camber by tightening the foot. To help grasp what is happening, it is also useful to have sensitive mast- head wind vane.

Once set, the vane tacking angles can be left untouched for all normal wind conditions. The only time you may want to fiddle with them is under special wind conditions. These are a.) very light or very heavy winds, and b.) winds approaching at a large angle from the direction of the windward board, i.e. when a reaching course would be preferred to a close beat. The vane tacking angle found by the procedure described above will be suitable for all moderate wind strengths, but, without changing the boom angles, the vane may be set for a slightly narrower angle (say, 2 degrees) in very light wind, and a slightly wider angle (say 1 degree) in very strong wind. The reason for this is that changes in boat speed are not directly proportional to changes in wind speed. If the wind speed doubles, boat speed will increase, but somewhat less than double. This, in turn, changes the angle between the true wind and apparent wind.

6 Of course, when the boom angles are changed, the tacking angle always needs to be changed to suit. In extremely light or drifter conditions, I prefer to ease the sheets to keep the boat moving at the expense of pointing a bit lower. At the opposite extreme, if one has no smaller suit of sails to use in gale conditions, it's also advisable to ease the sheets and point lower to reduce the yacht's heel. A yacht consistently pressed down to more than 30 degrees of heel will travel more slowly and lose much more to leeway. As a rule of thumb, most yachts are just putting a rail under when heeled at 30 degrees. Under either of these conditions, the tacking angle on the vane should be widened to suit the increased boom angle.

Figure 17. Asymmetrical Tacking

7 Aside from very light or very strong wind conditions, the second special wind condition calling for a change of vane tacking angles is where asymmetrical settings could be advantageous. This would be when the prevailing wind direction is so far removed from the main axis of the lake that you would like to be close-hauled on one tack, but reaching on the other. This is illustrated in Figure 17, above. For this condition, the booms will be pulled in close on one side, but let out further on the other side. The vane tacking angle for the reaching tack will need to be widened to correspond to the wider boom angle. Not all vane-steered boats can be set up this way. It requires that both jib and main sheets are passed through travelers on the deck, and that the travelers have adjustable stops for the sliding sheet fairleads. A boat with no travelers, but only single, fixed, sheet fairleads on the deck centerline cannot be set up asymmetrically. Even with travelers, not all Stobbe vanes have been built with extra adjustment room on the curved threaded rod to permit a wider tacking angle. If your boat does have travelers, and the vane does have the capability for extra-wide tacking angles, the same principals discussed above relating luffs, yarns, and tacking angles still apply. However, you won't have time to fine-tune it during a race, so you'll just have to make your best guess. Don't change the sheet settings, just control the boom positions with the traveler stops.

From these discussions, you will now see the importance of having an easily read tacking-angle scale affixed to your vane. The tacking angles found for a close beat are critical and worth preserving. Without such a scale, avoid any temptation to adjust the tacking angle settings after once you've found them, as you may lose the original settings and have to derive them all over again.

To recap, tacking upwind with the vane is primarily a question of properly setting up the vane beforehand. Once set up and adjusted, very little needs to be done at lakeside to sail a windward board:

1.) With the vane locked, rotate the vane to exactly the straight-ahead position on the vane base disk. 2.) Set the rudder-centering elastic to a weak tension, on the deck centerline.

3.) Unlock the vane.

4.) Set your main and jib sheets in their beating positions.

5.) Send the boat off with the sails full and drawing; some heeling is needed.

6.) Watch closely to see if the gying spring needs any more adjustment.

If the boat just doesn't seem to work properly, or behaves erratically, sometimes pointing just fine, and sometimes not, the cause is likely to be either a rudder not accurately set in the straight-ahead position, or else some point of friction or binding in the vane/rudder assembly. In the calm air of indoors, you should be able to easily activate the rudder by blowing on the vane feather from three feet away.

If a vane-controlled boat points well on say, the port tack, but the sails luff (i.e. flutter) on the starboard tack, then there is a fault somewhere in the vane set-up, the rigging, or in the hull. A number of possibilities exist. The degree scale obtained from calibrating the vane on the degree board (see Article 1) may be wrong. The tiller clamp-screw may have slipped or been set with the rudder slightly at an angle. The tiller-centering elastic may not be set on deck centerline. The traveler stops may be set unequally, allowing the sheets to move further out on one side than the other. The vane feather arm may have been bent. The forward portion of the tiller, which guides the centering elastic may have been bent. The vane-tiller-rudder assembly may have a point of friction where it binds up. The hull may have been built with an inaccurately placed keel fin or rudder skeg. The mainboom vang pivot at the heel of the mast may be off-center. This will cause the vang to be slack on one tack and tight on the other tack, which in turn may cause the sliding sheet fairlead to bind on its traveler. The same problem can result from the mainboom gooseneck being off-center. Everything needs to be carefully checked.

A common problem with vane-steered boats is to fail to complete a tack. When this happens, the boat typically makes it half way round, but then comes to a standstill, pointing straight into the wind with all sails flapping. This is known as being caught "in irons". Flapping sails are an effective brake, and will quickly stop the boat. Eventually, the boat begins to make sternway, moving backwards, and usually will fall back onto the tack it was on originally. The entire episode is known as "missing stays". Failure to complete a tack can be a difficult problem to solve. Some boats seem to be more prone to miss stays than others. Why this should be so isn't always clear, but appears to be at least in part, related to the hull design. Full-keel designs with rudders near the pivot point of the hull are more easily turned than are fin-keel-and-skeg designs with the rudder placed well aft. This can be immediately felt when turning a boat with a bamboo pole. In shifty winds, all boats will occasionally miss stays if hit with an unfortunate wind shift in the act of tacking. If your boat often fails to complete a tack, however, you will have to do something about it.

Before you change anything, check to see if any basic vane settings are wrong. Failure to unlock the vane (a common mistake) will invariably cause the boat to go into irons. Make sure the tiller-centering elastic is not too tight relative to the slack tension of the gying spring. If the boat has been in a collision earlier on the same board, check to see if the vane body has been forced away from the straight-ahead position on the base disk. (It will be necessary to momentarily lock the vane to check it's straight-ahead setting). If the vane set- up appears to be correct, then the cause of missing stays is more subtle, and will require a determined period of observation while trying various remedies (one at a time).

9 The first thing to check is the set of the jib. As mentioned earlier, the jibstay must be really taut. If this is OK, look at the curve of the leech, which may be too slack, causing the jib to spill too much wind. (Note that if you've just tightened the jibstay, you will have simultaneously increased the leech tension). This is best checked with the boat on shore. Hold the boat into the wind as if beating, and look down the jib's leech to observe its behavior during a gust. If the leech billows out during a gust, the leech tension should be increased. This is done by slackening the jib's topping lift if one is fitted, or increasing the forward-projecting portion of the jib-boom ahead of the boom's pivot point. If the mainsail becomes backwinded, you've made the jib leech too tight. If the jib leech looks good and needs no adjustment, then try moving the jib-boom pivot forward one space on the deck track. This will move the sail's center-of-effort forward, which will depress the boat's head and cause it to point a bit lower, but travel a bit faster. The greater speed will give the boat a bit more momentum to complete the tack. It will also cause the boat's bow to come around quicker once it has passed through the eye of the wind. Easing the mainsail's leech tension by very slightly loosening the sheet and/or the vang will have a similar effect by spilling some of the mainsail's wind. However, as this will reduce the sail's drive, it's best to first try adjustments to the jib, unless the day is so windy that the boat is being overpowered, in which case the mainsail may be usefully depowered. To miss stays may not be the fault of the vane. However, it may also be worth a try to slacken the gying spring a little (using the transverse adjustment). The reasoning here is that the boat may be trying to tack too soon without having sailed far enough to develop sufficient forward momentum. As mentioned above, flapping sails create a lot of drag and quickly slow the boat. A slacker gying spring will help the boat to stay on it's initial tack long enough to build up more speed, and hopefully, carry it's momentum through the eye of the wind to the opposite tack. If neither sail adjustments nor vane adjustments are effective, a third remedy to cure missing stays may be to install a "Liverpool Boy" (Figure 18). This is a light elastic cord attached to the tip of the jib-boom, ahead of the jib pivot point, or attached to a short arm sticking out perpendicular to the jib-boom on the weather side. The elastic is threaded through a bowser and run back to the side-stay chain plate, where it is doubled back to the bowser. The bowser is adjusted to provide just enough tension to hold the jib boom out on the "wrong" side as the boat passes through the eye of the wind. The idea is that, while the mainsail is still in irons, the jib is being held out to weather to catch the wind first and will help push the bow around onto the other tack. Once the boat is on the new tack, the wind pressure on the jib sail should overcome the strength of the Liverpool Boy elastic, and the jib-boom swings over to match the main boom. The Liverpool Boy is only needed on one side, the same side as the vane gying spring. Attentive readers will note (with alarm) that the operation is very like being momentarily "hove-to". All sailors know that to bring a boat hove-to fully stops the boat in its tracks, thus the risk of using a Liverpool Boy is that the selected tension may be too much, holding the jib boom out to weather longer than absolutely needed. The Liverpool Boy is disconnected during the run.

Figure 18 The "Liverpool Boy"

It's hard to say what solution will work for any particular boat. If the boat misses stays in only one direction, for instance, when turning from starboard to port, but not from port to starboard, then one of the many possible contributors discussed above for unequal tacking performance may be to blame. On a lake such as Spreckels, however, this is very difficult to observe, as all tacking is done along the north shore, and there is little opportunity to observe tacking along the south shore.

After sailing for the day, unlock the vane to relieve the gying elastic, and detach the beaded chain to relieve the tiller-centering elastic. The boat should never be stored with any tension on the elastic cords or else they will soon lose their elasticity. If you have used a rubber band, throw it away.

In my third article, I will discuss using the vane when running downwind.

Mike Stobbe, San Francisco Model Yacht Club, Aug. 30, 2010