Good to see we have someone else interested in sailboats.
We have an enhancement request here to add support for sailboats and I’m pretty motivated to make it happen. Philip Rowse is also working on a windvane. He showed me a picture the other day of it mounted on a thunder tiger sailboat (I have the same boat).
We will certainly need to modify the navigation code so that it doesn’t attempt to sail too close to the wind.
If you’re looking to implement something yourself until we built it out officially in ArduPilot then I think using Rover’s Guided mode would work. And then the arduino could send in commands to sail to locations so that the vehicle never tries to go upwind.