I would tend to agree with Wolfgang in general. Though we sailed a Dean 365 cat across from
South Africa many years ago without a
windvane, using an
autopilot, I believe that a
windvane could be used... particularly in downwind conditions. The trick on other points of sailing is to get a clear air flow and, with wide hard dodgers that cats typically have, that can be difficult.
Our cat was rigged for a
wind vane with auxiliary
rudder to drive the main rudders and, fortuitously, that saved our bacon when our
steering cable broke halfway across the Atlantic. Though the
wheel and
autopilot were disabled we were able to steer using the auxiliary
rudder for two entire weeks.
As Wolfgang says, it's nice to have redundant systems.
Ted Miller