Helm enclosure front window zipper?

[GordMay]

Greetings and welcome aboard the CF, Sandgroper.

[vorpal blade]

Do the inverted U and make the radius on the corners at least 10". Also get them to use a coil zip (most commonly seen on suitcases) not a Vislon-type tooth zip (like on a wetsuit). It could be they are suggesting straight zips as sewing around a radius is not as easy as it seems, sailmakers sew great straight lines. Sew around the outside edge first, sew and pleat the onside edge to match and then cut the opening.
A 9 coil zip with twin slides is probably the ideal.