Whether you are out in front defending or attacking from the back of the pack, huge gains can be made on the downwind leg of a yacht race. Making sure your spinnaker trim is fine tuned will help you get down to the bottom mark in a winning position and whether you have a symmetric or asymmetric spinnaker, understanding not only how to trim the sail but what angles to steer is essential for good VMG and gaining a competitive advantage.
We asked the experts at North Sails to give us a few tips on how best to trim your spinnaker downwind. One of the world’s leading sail designers and manufacturers, North Sails is well placed to help you get the most out of your sail, whatever the race track throws at you.
Symmetric spinnakers are very common amongst IRC rated racing yachts and are controlled by the spinnaker sheet, pole and guy. Understanding how to set up all three of these controls is vital to good downwind trim - use these correctly and in harmony and you’ll achieve good speed on the downwind leg of the race. This, of course, can be difficult to achieve and requires focus and attention to detail as you constantly tweak all three aspects according to your ever changing direction of course and wind shifts, but put the effort in and you’ll get results.
In most conditions you should set the pole so that it is at 90 degrees to the wind direction. This will change as you sail down the course, so your guy trimmer will need to be alert and ready to change the position of the pole constantly; if the shoulder is rolled out, and the foot is too round, then trim the guy to pull the pole aft, if the foot is stretched flat, and the tack is poking out to windward, then ease the guy to let the pole forward. Also, unless it’s very windy, the guy can actually be trimmed further aft than square to the wind to get the luff to run vertically from the shoulder of the spinnaker down to the tack, and to get the shape across the foot to match the mid shape.
In most cases you should fine tune your pole height to ensure the pole and tack are level with the clew. However, on a close or beam reach, try lowering the pole so the tack is lower than the clew (by a foot or more) to pull the draft forward and open up the leech giving you a faster reaching shape. Conversely, on a broad reach fly the pole higher, keeping the two corners (clew and tack) even. In a fresh breeze beware of flying both corners too high, as this will let the spinnaker get too far from the boat and may reduce stability. If the boat is rolling side to side, try lowering the pole, pulling the pole aft, and/or choking down the sheet lead.
The job of your spinnaker trimmer is to constantly ease and pull on the spinnaker sheet to ensure that the spinnaker luff is slightly curling at all times. They should never take their eyes off the sail, as tiny movements in boat direction or wind speed can cause the sail to quickly fill or collapse. Make sure they have a dedicated winch grinder who has their full attention so they can react quickly to trimming calls and have another crew look out behind the boat to call in the gusts or lulls to help the trimmer to preempt any changes.
Asymmetric spinnakers trim differently to conventional spinnakers. Flown from a bowsprit, an asymmetric spinnaker is controlled by the sheet, halyard and tack line. Some boats also have tweakers to choke down the sheet. Like with the symmetric spinnaker, high concentration levels are required to achieve optimum performance downwind and lots of practice and experience in different conditions will really help you to gain a natural feel for the controls and improve your performance on the water.
Asymmetrics don’t go dead downwind so optimum speed is achieved when you reach across the downwind leg, zig zagging down the course. Although you will sail further, the extra speed more than makes up for it. The optimum sailing angle can be as much as 40 degrees above dead downwind – nearly as wide an angle as we sail upwind, but sailing at these high angles increases the apparent wind, which in turn increases boat speed.
The trick is to build speed at an aggressive apparent wind angle, and then to push down to a lower course, with the boat speed holding the apparent wind forward. The driver and trimmer must coordinate efforts for best effect. As the load builds in the sheet, either from aggressive sailing angles or a stronger gust of wind, the trimmer should ask the driver to bear away, while easing the spinnaker sheet to unload the helm. As the load in the sheet drops, trim the sheet and head up to rebuild power and speed. Then once you have better speed, carry it down again. You should always feel the breeze blowing across the boat – not over the stern, so when you lose apparent wind flow across the boat, head up, rebuild speed and apparent wind, and slide down again. Continue to do this all the way down the leg and you’ll be on course for a good race.
We asked one expert trimmer for advice on sailing deep with an asymmetric spinnaker, and he said:
“Remember these three things: Ease, ease, and ease. Ease to a curl, pause and the curl disappears. Ease again. Carry a curl, and keep easing. Ease some more. Usually the sail stalls from being over trimmed. Ease.”
Regardless of the point of sail, the basic principles apply - ease to a luff and trim. Given the rapid acceleration, the apparent wind angle is changing all the time so aggressive trimming is required in order to keep up as the boat builds speed. An equally aggressive ease is needed to prevent a stall as the boat slows down - remember, over trimmed is slow.
On a close reach, trim to the telltales, or keep a small curl, and on a broader reach force the sail out to a bigger curl. You will be surprised how far out it can go.
At times, on a broad reach, it may also pay to ease the tackline a foot or two. This will allow the entire sail to rotate further out to windward. There are a couple of things to guide you in how far you ease the tackline: Does the sail rotate out to windward? Can you sail lower or faster? If the sail sags to leeward instead of rolling out to windward, then pull the tack line back down to the bowsprit. Likewise, if you lose control with the tackline eased, snug it down. With refinements in modern A-sail design, there is less of a need to ease the tack line these days, but experiment to find the optimum setting for your boat and sails.
As the true wind builds to around fifteen knots, you may be able to plane downwind, depending on your boat design and sail area ratio. Even for a dead downwind course, it will pay dividends to reach up onto the plane and carry optimum speed. Your fast planing speed will overwhelm the extra distance sailed to get on a plane, and see you move ahead of the fleet. On the other hand, if the winds are light and you can’t plane, don’t waste energy going the wrong way. There is a fine line in achieving the best angles downwind with an asymmetric spinnaker, but practice and experience of different weather conditions will help you to get a feel for your VMG settings.
Overall, understanding spinnaker trim and the impact it can have on your downwind performance is crucial to a good race. Finding your optimum trim settings and steering angles will propel you up the fleet and help you to improve throughout the season. Every boat and sail is different, so it will take time to find the optimum symmetric or asymmetric settings, for all of the different weather conditions and race formats, but if you put in the effort to fully understand your spinnaker trim set-up, you’ll get closer to the results you want on the race course.