Hi there,

(translated from Portuguese)

Luiz, please check if my answer is worth posting. I'd rather not start too serious a controversy - only healthy discussion. I'd really have no time for it and it is not without a certain sacrifice that I write those texts. Please use a spell checker in my replies because I have none in my computer. My English is rusty because most of the texts I've been writing lately are in French.

If you find anything too strong, please take it out.

Regards,
Arnaldo,

(end of translated text)




Dave Calvert’s paragraphs on the way he arrived to a best all around design are perfect. They help us in understanding that there is no basic contradiction between the quest for an “all around sail” and the creation of a sail with the ability to change its geometry. Such a sail would also be “an all around sail”. The difference is the following: whereas Dave’s way considers the sail geometry as essentially fixed and relies on the rigging for sail shape control; I believe that the sail itself can be part of the solution.

In his description he says:



A sail that could self flatten in the breeze would enlarge its useful range, possibly to a wider extent than could a “fixed geometry” type of sail (since the latter would rely only on rigging changes for shape control).

He then follows the thread by saying:



Whereas PHRF sailors may refrain from buying many different sails, a great number of classes indulge in a frenzy of specific sails. Tornado is one of these classes (especially for jibs), but even old designs as the Snipe do follow this trend - not that I agree with it. I'd rather keep sail inventory to a minimum. What I say is that nowadays many classes admit that a great number of sails may be necessary for a boat to be adequately competitive.

Then the question of the Tornado sail comes back:



First of all, a correction and an apology. I wrote that Zuccoli Tornado sails cover a very limited wind range. I was referring to the jibs. The mainsails do show a wide range of use, for reasons explained below.

In fact, if the Tornado sail I mentioned (99% of the boats use it) WERE flat, I would totally agree with Dave. It happens that a Zuccoli mainsail is NOT flat when set on the mast. It’s just its construction that is flat. The flying shape is not, due to the battens, to the mast and to a small number of almost secret details. The conclusions are far reaching, as they mean that you don’t need to put draft in a sail to see draft when the sail is properly set (*). Zuccoli mainsails are reasonably full in light winds and no one can deny they are a blatant success. But since they are (1) radial and (2) built flat, they respond much better to luff tension, outhaul tension and mast bend than previous sails. It was Dave himself who wrote:



What he is describing is - precisely - a sail that has variable geometry, that is, a self-flattening sail. The only mistake, in my opinion, is his reference to a “stable cloth”. Is is precisely because the sailcloth stretches that the sail geometry changes. The merit of Zuccoli and some other sailmakers, is to have devised a construction of sails in such a way that cloth flexibility is an aid in the control of sail shape, rather than an enemy to fight.



Keeping with the example of Zuccoli sails, it seems that the self-flattening ability of his mainsails could not be emulated on the jibs. The reasons may not fit in the present discussion, but the absence of an efficient way to tension the luff, together with incorrect cloth choice, may account for it. The fact is: one needs to have as much as four different Tornado jibs to work with a single mainsail. For me, this is a clear demonstration that these jibs could profit from a different approach, as construction techniques go. Of course the boats might also have to sport new trimming resources.

The subject than changed to low stretch and low weight:



Dave correctly states that low weight is always better and that is a sought-after characteristic in most sailboat classes. But my question was rather: why BOTH characteristics (lightness and low stretch) at the same time? I still think that a careful choice of sailcloth flexibility, with more stretch on the leach (for instance) may widen the useful range of the sails.

Then comes a new question:



I'd rather refrain from commenting on the exact details, but as you can certainly figure, building features like this into a sail requires a lot of skill and is a labor intensive task. Basically, one has to start by abandoning the pre-conceived idea that cloth flexibility is always bad. Once it is assumed that flexibility can be put to play in your team, instead of against you, the rest will follow - not necessarily in an easy way. But with a researcher’s mind and A LOT of experimentation and hard labor, one can eventually develop a consistent way to create self-flattening sails.

Remark: it may is interesting to note that also on the boats side some improvements are necessary. The powerful purchase on the luff tensioning system of the Tornados is one of these changes.

Cheers

Arnaldo

(*) I said above “you don’t need to put draft in a sail to see draft when the sail is properly set”. This is not new, of course. It has been known for about 3000 years. But the submission of human intelligence to sailmaking softwares is somehow erasing this information from the minds of otherwise well informed sailors.