Actually F18's and other have similar devices as well. It is very noticeable on this Ullman sail but since then I've recognized similar things in sails of many other designs. Pretty much the leech load on a large squaretop sail is about 400 kg. If all of that or most of it is taken up by the batten then you would simply push the batten through its cap on the luff and jam it into the luff rope and sail track. This is actually what happens on my sail when I use stiffer top battens to flatten the sail. I had to bolt the whole assembly up to repair this issue. Since then I've stopped used stiffer battens to flatten out the top and just found other ways (trim) to get a similar effect.

The Ullman sail has two of these tapes in the sail and overdid it. The top of the sail (squaretop) now just weathervanes even in sub trapeze conditions and now amount of leech tension can bring it back. Together with the owner of the boat we looked long and hard at it and even put the boat on its side and cranked on the mainsheet to see what happened there. The top 500 mm just flaps about in the wind.

Personally I think this setup may be regard both as a benefit and a serious drawback. For a novice sailors this sail is very easy to use as it is impossible to oversheet the mainsail which would make the boat feel really bound up and slow. Additionally the boat is mild mannered. The drawback is of course that a capable crew is blowing off power that they otherwise could use to become really competitive. Double trapezing upwind is extremely rare with this sail. It seems the experience is that it is surprising good for singlehanded sailing but a little underpowered for doublehanded sailing. Pointing with it is difficult as well. Probably because the leech falls aways too soon. Careful mast rotation control and really well adjusted downhaul can get it back up to speed and recover some pointing (when doublehanding) but it is difficult.

It is not a bad sail but it was expected that a renowned sailmaker like Ullman would have come up with a more convincing design. In my personal opinion the new Glaser sails are heaps better. And I would even go as far as to claim that the recent achievements by Matt and Gina McDonald are to a significant extend the result of switching to a Glaser main sail.

I think Ullman needs to look at the experiences with this design and develop a new F16 sail that adresses these issues. If it remains as it is now then it will not be comparable to competing designs from Glaser, Ashby and soon enough also Landenberger.

Wouter