autopilots

[Blue_Heron]

... generally anyone else on the boat can not keep a true coarse while I am setting out lines and rigging...

I know I'm not answering the question you asked, but...

I set a course, put a buddy at the helm, hand him a beer, point to a cloud formation on the horizon dead ahead and say "steer toward that". This approach works best if you pick the crew member with the longest attention span.
Dave