I'm also curious about this. There seems to be no information out there on sailing the Mexican east coast. Check out publication 148 from the National Geospatial-Intelligence Agency
. It says:
Puerto Veracruz, Tampico, and Coatzacoalcos are the principal ports for large vessels, but there are also several small ports for vessels with shallow drafts.
Where are those small ports? I would like someday to sail out of Corpus and visit the Mexican east coast.