Going into a new port at night, you may be safe relying on the
GPS for navigation, but it is a good idea to back it up with visual markers or, at a minimum,
radar.
Last year I was coming up to the Marieta Islands near Puerto Vallarta sometime before daylight. Several miles out, I noticed that the
radar showed the island over a mile in the wrong place. I thought the
radar might be broken.
I slowed down to arrive after dawn. (You can see the jags in the boat track at the bottom of the screen where we were floating around.) It turned out that the
GPS data (Navtech) and the admiralty
charts show the islands more than a mile off their true position. I am glad I noticed this sooner rather than later, because the shore is rather rocky.
Marietas Islands, west of Puerto Vallarta
The Rains' Boating Guide to Mexico shows the islands in the correct place.