North Sails NEWS
Sport boat asymmetric spinnakers (also known as “kites”) trim differently from conventional spinnakers. And due to their extended, fixed position bow sprit, they differ from a cruising asymmetric flown from the stem.
Aside from the sheet and halyard, the only other control over spinnaker shape is the tack line, which runs from the end of the sprit to the spinnaker tack. Some boats also have twings to choke down the sheet.
Reach Up to Go Downwind
Asymmetrics don’t go downwind, at least not dead downwind. The fastest way to reach a downwind destination is to reach up and sail fast. The extra speed more than makes up for the extra distance. The optimum sailing angle is as much as 40 degrees above dead downwind – nearly as wide an angle as we sail upwind. Sailing at these high angles increases the apparent wind, which 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. As load builds in the sheet, either from aggressive sailing angles or a puff, the trimmer should ask the driver to bear off, 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. Get speed, then carry it down. Work up to rebuild, and drive down again.
You should always feel the breeze blowing across the boat – not over the stern. When you lose apparent wind flow across the boat, head up, rebuild speed and apparent wind, and slide down again.
For best broad reaching performance the sheet must be eased to allow the sail to roll out to windward. As the boat bears off, ease the sheet to take pressure off the helm. As you head up, trim the sail to add helm and bring the boat up.
Ease, Ease, Ease the Sheet
We asked one expert trimmer for advice on sailing deep with a sprit boat, 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.”
At times on a broad reach it may also pay to ease the tackline a foot or two as well. This will allow the entire sail to rotate further out to weather. There are a couple of things to guide you in how far you ease the tackline: Does the sail rotate out to weather? Can you sail lower or faster? If the sail sags to leeward instead of rolling out to weather, then pull the tack line back down to the sprit.
Likewise, if you lose control with the tackline eased, snug it down.
Note: With refinements in design and A-sails purpose-built for VMG sailing, there is less need to ease the tack line.
Marginal Planing Conditions
As the true wind builds to around fifteen knots, you may be able to plane. Even for a downwind course, it will pay to reach way up to get on a plane and then carry the plane down. Your planing speed will overwhelm the extra distance sailed to get on a plane, and crush the competition. On the other hand, if you can’t plane, you will waste plenty of energy going the wrong way… only practice and experience will teach you the best angles for your boat in a given condition.
Ease and trim
Regardless of the point of sail, the basic principles apply: Ease to a luff and trim. Given the rapid acceleration of sport boats, the apparent wind angle is changing all the time. Aggressive trimming is required to keep up as the boat builds speed, and an equally aggressive ease is needed to prevent a stall as the boat slows. Overtrimmed is slow.
On a close reach, trim to telltales, or keep a small curl. On a beam reach, the asymmetric is much faster than a symmetric spinnaker. On a broader reach force the sail out to a bigger curl. You will be surprised how far out it can go.
On a close reach snug the tack to the pole for a gennaker shape. On a broader reach, add power and allow rotation out from behind the main by easing the tack line a couple feet.
There are a couple of clues to indicate how far to ease the tack line:
- The tack should pull to windward as the tackline is eased. If the tack sags to leeward, keep the tackline down.
- Easing the tack line adds power, so in light air you may want to ease it a little even on a beam reach. Broad reaching in a big blow, you probably will want to keep it tighter than you would in lighter air.
- Another valuable guide is the spinnaker telltales. Add telltales 1.5 to 2 feet aft from the luff at 1/3 and 2/3 height. When your tackline is set at the proper height, the telltales should behave similarly high and low.
Let’s Go Fast
Truth is, there is more to it than point and trim. Often you can use techniques similar to those described for upwind VMG sailing to improve speed on a reach. Here’s how:
Rather than simply point and trim, head up slightly to build speed and apparent wind. As speed builds the apparent wind will build and move forward. As the apparent wind angle goes forward you can drive off, carrying the extra apparent wind speed and boat speed at a lower angle.
When performance cycles down, heat it up (head up) again. Rebuild speed, and drive off.
The trimmers and driver must coordinate efforts to optimize performance. If the helm loads up, it will be difficult to drive off. As speed builds the trimmers will need to ease to allow the boat to drive down without loading up the helm. Similarly, trim the sails to help head the boat up, rather than steering too much with the rudder.