I've been thinking about it some more and realised there is another aspect to the functionality. A couple of other points are...

Without the reinforcement tape, the leech tension would still be transfered to the head along that bypass route more than over the top of the head, but the sail material would stretch more.

This tension along the bypass route also holds the batten relatively straight where they cross. Imagine the bow string analogy (that's a good term for it) with an extra bow string going along the bypass route and fixed to the batten where they cross. The batten will be held there and bend either side of it. You can see this if you capsize your boat on land and crank the downhaul on till the top is completely flat and the batten starts to behave funny, it may even invert.

Back to the original question.

If you look closely at the panel configuration of the sail you can see the panels closest to the luff appear to converge at the head of the sail at the halyard lock. But look at the panels towards the rear of the sail & you can see the panels start to depart from the head point & spread out over the width of the head. Ullman have simply put the reinforcing tape to help the panels that do not align with the head board. Radial sails need the seams to be as close as possible to the load lines as the maximum strength is primarliy along these lines. It is extremely difficult to satisfy all the loads at the top of these sails & I dont believe any sailmake has solved the problem......but it looks as though Ullman are heading in the right direction by covering both bases as you can not configure you panel layout to the forward head of the sail as the material in the upper panels with self destruct in a short amount of time & sailors will be pissed off. <img src="http://www.catsailor.com/forums/images/graemlins/mad.gif" alt="" />

Most sailmakers (they are generally restricted by their software)will spread all of their head panels evenly across the head of the sail & try and get the head reainforcing to pick up the shortfall that occurs as a result.

An interesting point out of all of this is that F18 would not allow this type of construction as I tried to enquire about a tape drive style of sail & was informed that if the sail was likely to cost more the class rule was likely to prohibit it. <img src="http://www.catsailor.com/forums/images/graemlins/confused.gif" alt="" />

Ok, thanks again Marcus.

So the reinforcement is there to take off-axis loads from the cloth. Much as suspected, but it would be very interesting to see the result from a finite element stress calculation.


Adding some high modulus tape like this can not drive cost up much(?) Doing a tape/string sail on the other hand.. But prices are dropping there as well.