"luc" wrote in message
ups.com...
who cares what the rudder does, as long as the boat is going in the
right direction?

How true. However sometimes the boat is not going in the right
direction! Now, a decent autopilot has to "think" how quickly the "wrong"
direction came about, how long does the Captain want to wait until we are
back on course, how many over (or under) steering swings he is comfortable
with, and how often these course errors are taking place.
How much should the autopilot move the rudder to achieve what makes the
Captain happy? How does the autopilot know when the rudder's pump or grinder
has moved the rudder to the correct position? Computer determined timed
motor runs are often used, but are not nearly as accurate and positive as
simply telling the "Iron Mike" where the darned rudder is at all times!

Old Chief Lynn