Bryan,

I don’t pretend to be an aero-dynamist (spells?), so I just roughly follow ordinary textbooks about sails. And yes, I have telltales along the leech which tells me when I over-sheet and when I am fine.

Cutting off the yard? Njet.

Reason 1: By shortening the yard to make the top square, the compression on the top battens rises. Stronger battens needed:

Reason 2: At least for the rig I make, the yard must not be shortened or it may fall forward of the topping lift when I reef to 3-4 panels.

Reason 3: Why change something that works? The power and closewindedness of the three top panels have surprised me many times.

Arne

David Tyler wrote:

I haven't seen it in the flesh, but on paper, Top Notch 9 looks like a strong contender to me.

Sebastian used Weathermax on Peregrine.  I laid hands on some the other day and it feels very nice to me.  Comes in a fairly wide range of colours, too, and is half the price of acrylic, at NZ$30.50 a metre at 152 cm.

They yard has an interesting provenance.  It started life as a yard - on a square rigger - then became the main mast on a boat that circumnavigated about 25 years ago, with a young family aboard, before ending up as Fantail's yard.  If you decide not to use it, can I have first refusal, please? :-)

I wonder what you both think of shortening the yard and truncating the top panel, leaving the upper edge of the top panel horizontal or nearly so. While the peak of the sail may provide some roll damping on a Bermudan rig I can't see much value in the cloth in the peak of the sail in our case, and retaining Fantail's current yard is appealing. 

David, the foil shape is a something I'm not confident about at all, although it would be a good moot point over a beer and chips. I wrote a long reply as to why I was considering changing it, but deleted the response as both the explanation and justification was poor. In essence I was considering doing something about what I perceive to be Fantail 's greatest weakness - windward ability in chop, slop and swell. In writing it all down I feel less certain that I want to go down that path.    

In a previous life I worked in aerodynamics and computational fluid dynamics; I had a well equipped, 400 square metre workshop to play in and I am a compulsive tinkerer. I'm waiting for issues to be resolved around the rebuild of my house post-earthquake and have time on my hands, and there's something compelling about trying something new... but I am very aware that experience counts for more than theory.

David Tyler wrote:I'd be looking around for a polyester cloth with as little filler as possible.

I'm planning to use Marlen Top Notch 9 for my new sail. It's a "solution dyed polyester fabric with a fluorocarbon finish, resulting in a fabric that is breathable, reversible, water repellent and has a luxurious hand". Weight is 9oz - I believe Dave Zeiger used the 11oz version for his last sail.

About the same price as Odyssey (or a little more) - for which the manufacturers recommend only one side should be exposed to the sun.

Any opinions?

Chris

For some reason, which I have forgotten now, back in January I drew up a modified Fantail sail. It has a less aggressive yard angle, which should make it easier to set, with less loadings on the LHP and on the cloth in the throat area. It also has a straight leech in the sheeted panels, which should make for less snagging when reefed.

Odyssey is basically polyester cloth, like "Dacron" sailcloth, but is very much more loosely woven and depends on its impregnation to keep it stable. Thus, it is still suitable for sails in which the bias stresses are low, but as we now know, not so suitable when the sail design is such that there are larger, cyclical/reversing bias stresses. I don't think I could recommend it for the above sail, even though those stresses would be less than in Fantail's current sail. I'd be looking around for a polyester cloth with as little filler as possible.