Tension meter or musical note
We bought a tension device from West Marine that I've seen frequently used in our marina. The Cat 30 Owners manual says something about creating enough tension to hear a musical note when "plucked." Master rigger, Brian Toss, has a book with some vague descriptions on proper tuning. In the end I went with Larry Pardy's observation, "a straight mast is a strong mast" and used the tension meter to put equal tension on upper and lower shrouds.
