Well, when we actually build test sails we use venture tape and sew the seams.

Seams are much wider than a radial sail but all Maxx/Flex sails have wider seams than radial sails.

Attached is a pic of a sail that we have been using for 3 years now and the mainsheet loads on this boat are the same or higher than a Tornado. Seams are done with venture tape and stitching. no movement yet...I think you can even see the stitching on the vertical mitre seam.

Education continues <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

While we're at it, in your professional opinion and based on your experience with Contender, does a 3DL sail have broadseams?