Sail cloth

[Analgesic]

I am in the market for a new main sail.  I have tentatively put in an order with North Sails Direct-they recommended 8 oz Nordac cloth.  I then saw the Fx Sails web site which quotes standard Catalina sails and for the C-34 they recommend 7.3 oz Dacron.  I would be interested in any information on what conditions the different sail cloths might be best for.  I sail in New England, most often 5-12 knots wind but frequently reefing in the low 20s and every Summer at least once or twice I get caught in around 30 knots.  It's not to late to change my order if there is good reason. 
Brian McPhillips

[Ted Pounds]

Nordac is just North's brand name for their Dacron (NORDAC = NORth DACron).  It may have a slightly different, proprietary weave, but it's basically the same thing.  And the difference between 8 oz and 7.3 oz is negligible.  So, if you're happy with the service at North Direct, stick with them.

[Jon Schneider]

The only way to really tell is to get samples of each fabric and decide for yourself.  As long as you're not a competitive light-air sailor, you're probably better off with the heavier fabric, assuming there's a correlation with lower stretch.  That said, stretch is more based on the weave than the fabric itself.  Another consideration, if you believe the two sails to be relatively similar is to ask where they're made.  I'm not trying to be overly jingoistic, but if one is made locally and the other is made in another part of the world, I would go local. 

[Ron Hill]

Brian : For a Main I'd definitely go with the heavier material.  It's less likely to stretch in a blow and is still OK in light air. 
Beside the weave that Jon mentions, I'd guess that the woven threads are also thicker - helping  contribute to less stretch.