I've been waiting for this topic to come up again-
I decided this spring I had to go after the "water spots" on my (14) year old fishing boat (not a Hatt). I was hoping for a chemical solution, the majic bullet that got it done with almost no effort. Nothing worked. After more surfing, I read of Spot-X. From their on-line speal, I thought I was buying a liquid with majic bullet tendancies. Well it turned out to be a pumice-like powder that you make a thick paste from and apply with their pad (sorta a less course version of scotchbright).
Bottom line is my windows are spotless now; the stuff works- but not without elbow grease. You need a 1/4 sheet palm sander for large areas (all Hatt windows are large areas). Mine is the famous Porter-Cable finish sander. Figure about 8 sq-ft per hour (this does two applications, which I needed).
I'll be doing my 89' sports car next. One of those "new car" things that slowly goes away with age is the perfect glass. Obviously, the problem is not limited to salt spray. Mineral content from potable water and rain water is enuf to do the damage.
Gary
p.s.- the stuff is also great on stainless rails- it is probably very similar to compounds used to attain fine finish of polished metals.