Evolution Autopilot unable to hold course in waves

[wstigg]

Hi Forum - Forgive me if this topic has been covered elsewhere. I searched for a bit but found nothing.

My new Evolution AP system (EV-1, ACU400, P70, rudder reference sensor, Type2 Linear drive) in concert with the rest of my ST60 instruments does a swell job holding course in flat water and in moderate waves. When reaching and running in a fresh breeze with waves over a couple of meters, however, the AP struggles. When the waves are over 4 meters, the system can hold a course +/- 25 degrees in leisure mode and +/- 35 degrees in performance mode. Odd that performance mode is worse than leisure.

I can hand steer in these conditions, holding a course of +/- 10 degrees, using very little rudder, but anticipating the waves and making small course corrections before the waves lift the stern and send us surfing down the hill with neutral rudder.

Leisure mode comes closest to hand-steering, but it is still using 3 times as much rudder. Cruising mode is more active on the helm and performance mode seems to be hunting all the time.

We are a Carl Schumacher designed, performance monohull sailboat, 48 feet x 30,000 lbs. In the problem conditions, we are moving at 10 - 11 knots and surging to 14K and up. Sail plan is well balanced.

All components are running latest software builds, except P70 which is at 3.05. (Differences between 3.05 and 3.07 don't appear to be significant to this issue.) ST60 boat-speed is calibrated and accurate.

I've been through the entire dockside setup and linearization process successfully. Deviation on EV! shows 7 degrees.

I have selected Vessel-Type = Sail. Should I try a different Vessel Type? If so, what type might offer good course-keeping?

It sure seems to me that with good rate-gyros sensing pitch, yaw, and roll, sooner than I can feel them, that the system should be able to steer as well as I can in these difficult conditions.

Any help/advice is welcome! Thanks, Willy