Our worst experience by far with weed and the
autopilot was crossing the Atlantic when the weed masses were as large as a foot ball field. Our first indication at night was the
boat yawing, and speed dying rapidly, and the "off-course"
alarm going off. Our first reaction was generally to reverse both engines when we'd generally find the weed was blown away. During the day when we could see the masses, we'd try and navigate around them either with the
autopilot in 10 degree increments, or by hand as required. Our
Raymarine AP and integrated systems worked well. Around the islands in the
Caribbean not so bad, and we only
cruise by day so can see the masses and anticipate what might occur. The much larger problem around the islands is the hundreds of poorly marked and randomly laid
fish trap floats often consisting of a couple of clear plastic large-size soft drink bottles that are hard to see. You need to keep a good lookout as we had one foul our port prop but we were able to untangle it without too much problem using our
SCUBA. They can be laid in waters up to 90M in
depth so being well
offshore sometimes doesn't help!