Elvstrøm downwind sails are renowned for their stabilty and therefore speed and performance. These tenets are just as important racing or cruising - an unstable sail is difficult to trim, and is therefore usually slow.
In racing terms this ease of use can be translated into straightline speed, and a tolerance to wind or directional changes - in the fast and lively boats of today, this becomes a very important factor in downwind speed. No wind tunnel testing can predict this, so results from this source need to be interpreted intelligently, and on the water testing needs to be exhaustive.
In cruising, all of these attributes allow for the sail to be trimmed less frequently, and be much more forgiving.
Asymmetric spinakers have given a great deal of fun and speed to all sorts of boats. They heel the boat less, and are more efficient, especially at tighter wind angles. Gybing is easier, and although the boat slows a little more than with a spinnaker gybe, it can be done with less crew. Early examples of Asymmetrics were difficult to trim and could be a little unstable, this has been eliminated on all Elvstrøm asymmetrics, racing or cruising. It is important for your enjoyment of these sails that they are well designed - there is a large difference between a good asymmetric and a poor one!
The panel layout is extremely important part of any downwind sail. As with upwind sails, the stresses and loads on the surface of the sail can be mapped out. The panels must be laid as carefully as possible to these stress lines, ensuring that changes in angles are kept to the minimum.
Within reason the greater the number of panels, the smoother, faster and more durable the sail will be. This involves a longer time to construct the sail, both in cutting and sewing, and increases the cost - it is the single biggest factor in the price of any downwind sail.
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