During our trip, we had a lot of windy nights. A lot. I can't believe it took me nearly three weeks to figure it out, but my Android phone from Telcel is actually a useful tool for these.
There is an anchor watch function on our chartplotter, but even with the brightness turned way down, that thing uses quite a few amps. My phone, OTOH, once it's charged up, (usually done while we're running the genset to make water or run the fridge) uses none. I just load up the Navionics charting app (<$30 from the Android marketplace), turn on tracking, and go to sleep. Every so often I wake up and look at this:
Nope, not moving.
There are also several anchor watch apps in the Android marketplace, which will presumably set off an audio alarm if you start to drag. I'll probably look into those (most require the substantial investment of something like $5, so why not?) but honestly, when it's windy, I'm not going to be sleeping for very long at a time.
BTW, if you don't want to get a Mexico phone with a data plan, if you already have the Navionics app on your US phone, the GPS and plotter functions will work without requiring a data connection.
We are surviving the winter - hah!
1 month ago