Techelet Tzitzit Tying Customs
Often tallit buyers who opt for techelet for the first time are unsure about the various tying customs.
For Sephardim, we follow Ptil Tekhelet Association's recommendation that they adopt the Rambam tying custom, also known as Yemenite tzitzit. Rambam/Yemenite tying can be done with either 7 chulyot or 13 chulyot (scroll to bottom). The traditional Sephardic tying custom used for all-white tzitzit is not recommended for techelet. Some Sephardim opt for Ben Ish Chai tying, which is similar to Chabad/Arizal tying, but with a spiraling ridge, and more spacing between the chulyot.
For Ashkenazim we usually tie techelet either according to the Arizal, which looks much like regular Ashkenazi tzitzit tying with a 7-8-11-13 windings pattern, or else according to the Vilna Gaon (aka "HaGra") or Sefer HaChinuch.
Vilna Gaon and Sefer HaChinuch tzitzit look quite similar, with alternating segments of white and blue chulyot throughout. With the Arizal tying custom, almost all of the twists are blue.
Also, according to the Arizal you wind up with seven white strings and one blue string, whereas with the Vilna Gaon (click here) and Sefer HaChinuch, you end up with six white and two blue.
A further option is the Raavad tying custom, which alternates white-blue throughout, broken up by five double knots, much like the Ashkenazi 7-8-11-13 custom for white-only tzitzit.
Note that the term "Raavad" can be somewhat confusing, because when sold separately, Ptil Tekhelet tzitzit strings come in two versions: Rambam and Raavad. The Rambam type is used not only to tie Rambam, but also Arizal (sometimes referred to as "Radzyn" or "Chabad"), and likewise the Raavad type is used to tie not only Raavad, but also Vilna Gaon, Sefer HaChinuch and other customs.
Another option is Tosafot (labeled "Raavad 7" in the photo below), which uses two full strings of blue on each corner, and consists of just seven chulyot. Because this approach uses twice as much techelet, the cost is considerably higher.
A further option is Amram Gaon, which is a very straightforward approach of 13 chulyot tied in a single unbroken section, with a standard double knot at the top and a tucked knot at the bottom.