radial design
The "tri-radial" design simply means the the corner panels in the sail are cut to radiate from the attachment points. This allows numerous panels to be aligned vertically with the luff and leech, and horizontally with the foot. The great benifit in this design is to allow stronger, heavier panels of cloth to be placed in the higher stress areas of the leech and foot, and lighter weight panels to be placed in lower stress areas near the luff and center of the sail. This "step-up" construction has been used in racing sails since the mid 80's. As it applies to cruising sails let me quote from Tom Whidden's "The Art and Science of Sails"...... "The step-up construction allows the heavily loaded leech and the foot panel--the latter being vulnerable to waves breaking over the bow-- to be made of heavier cloth. The panels get lighter and, at the same time, show less strength moving toward the luff (this part of the sail is less highly loaded). The result is a sail that is stronger for its weight. This is so important because the cruising sailor is now demanding a headsail that has the same range as a main, that is , not so heavy that it fails to work in 5 knots or so light that it stretches dramatically or evern self-destructs in 30 knots. Such a hybrid headsail is impossible without step-up construction. "When roller furlilng, one other benefit of the vertical sail with the radial clew is that the leech and foot panels can be made out of special UV-resistant fabric. With cross-cut lay-ups, a separate UV-resistant panel must be sewn to the leech. This vertical panel sewn across the horizontal panels that make up the leech adds unnecessary weight, compromising the performance of the sail in light air."Performance is the difference. Longevity, I believe, is affected more by the sail's cloth type, its care and mainenance and how it's used -- rather than by its design.Cost justification is an individual decision.