that's a very pretty quilt, and I've done several similar. It's not Y seams, it's a lot of rows sewn on diagonal and then sewn together into 8 pointed sections. What I dislike the most is no seams nest, so you need to be extra careful getting them lined up when sewing rows together. It does require more exact sewing than most, and getting a tiny bit off can cause you to end up with edges starting to curve and then you don't get a flat piece when you are done. One method is to break it down to larger diamonds and trimming them to exact size before sewing more together.