just me wrote:
I have a 7001 smart pilot and a RL80CRC at the helm on my sailboat.

Everything worked well for about a year and then one day with the autopilot
on, the helm went hard to port. I quickly put the autopilot on standby and
brought the boat back on course. When I looked at the plotter, the image of
the boat was showing the boat going sideways thru the water.

I went back and re-calibrated the autopilot and that corrected it.

During a two day sail, the second day it did it again. Has anybody
experienced this? Any ideas of what's going on and how to fix it?

experienced this behaviour on 3 different boats.
2 times the power connections to the autopilot-computer where too small,
rewiring it with 4mm2 strong wires helped
1 time problem was solved thru software upgrade (changing chip in
autopilot-computer