Zephyr Sail Evaluation

Chris Salthouse kindly provided an independent assessment of the new sail. His report is below.

Objective ;  Evaluate a new computer designed, machine cut sail against a standard class sail cut off the existing pattern.

Dimension Comparison: We layed the new prototype sail over the existing class sail. Both sails had the same length luffs and only a small variation in leech and foot lengths, the test sail being 10mm longer on the leech and 15mm shorter on the foot. Batten positions were similar but not identical, the top two pockets being 70mm lower on the prototype sail. This would make little or no difference to the shape of the sail but could be shifted on subsequent sails to match the existing class standard. The prototype sail also has 25mm less roach at the second to top batten. These are all fairly small and insignificant differences and in actual fact the prototype sail is closer to the original sail plan than the existing class sail.

Shape Comparison: Using the same set of battens we looked at both sails on the same rig. The prototype sail having a top stripe depth of 14.2% @ 40% back from the luff and a bottom stripe depth of 14.1% @ 37% back from the luff. In comparison the class sail had a top stripe depth of 13% @ 41% back from the luff and a bottom stripe depth of 13.1% @ 40% back from the luff. Making the prototype sail a little deeper and slightly more draft forward. This is due mainly to a little more luff curve.

Summary:  I think the differences between the two sails would be difficult to detect on the race course, they are certainly close enough dimension wise. The only suggestion I would make would be to maybe reduce luff curve on the prototype sail about 10-15mm which would bring it back very close to the existing class sails.

I feel that making the change to computer designed and cut sails would be a great step forward for the class in terms of consistency, Doyle Sails have done a nice job here of reproducing a sail very close to the original shape and specs. With the small luff curve change I believe the new sails will be equal in performance to the existing class sails with the bonus of being the same size and shape year after year.

Regards

Chris Salthouse
6 September 2006

Update 30 November 2006

Following the luff recut by Doyles as recommended in the above report we re-photographed the test sail with the same set of battens and on the same spars.

The recut sail now has a top stripe depth of 13.4% @ 39% back from the luff and a bottom stripe depth of 13.3% @ 40% back from the luff. This is almost identical to the class sail which had a top stripe depth of 13% @ 41% back, and a bottom stripe depth of 13.1% @ 40% back.

I was happy with the overall shape of the sail and it is most unlikely that there would be any detectable performance differences between the new design and the existing class sail. I would therefore have no hesitation in recommending the adoption of the new design with whatever cosmetic refinements the class may feel are necessary to preserve the appearance of the sail and allow the existing battens to be retained.

Regards,

Chris Salthouse

December 2006