I purchased an Autopilot ST4000 in January, 2003 for my ODay 39 which specs out at 18,000 lbs. It was professionally installed. The ST 4000 has not worked for two seasons. I have been in touch with Raymarine customer service quite often but they don't seem to have an answer. It tends to be try this or that. The first problem is that it won't track under sail or under motor. It will either snake under motor or veer severely off course under sail. Late last summer after sending the head unit to Raymarine it started to work but the post that guides the gear process that attaches to the wheel keeps popping out. It didn't start popping out until after it started to track correctly but when I tack it appears to put too much pressure on the wheel insert and pops out. They sent me a new post and suggested it was too short. I am going to install the new post this next couple of weeks and test it. I am wondering if anyone else has had difficulty with this particular autopilot. Thanks Bob H.