 We chug along at around 10 miles an hour. Over the loudspeaker, the automated tour begins. We're 52 miles from the Gulf of Mexico and the open sea. Just a few short hours, these large cargo ships make their journey to the end of the channel. We're not going the whole 52 miles down the channel, Lisa Ashley Daniels with Port Houston tells me. We step outside onto the dock and pass aging warehouses and city docks.