Rio GrandeThe vowel sound "aye" is easier and more dignified to sing than the vowel sound "ee", at the top of your lungs on an open deck. Therefore some place names were creatively revised in the sea chanties. The Peruvian port Ilo (pronounced EE-low) became Hilo (pronounced HIGH-low), and the Rio Grande (REE-oh GRAHND-ay) became the RYE-oh GRAND.
The Rio Grande referred to is not the river separating Texas from Mexico, which would be rather difficult for a sailing ship to navigate. It is the much larger river down in the Argentine of South America.
I can't beat Richard Kopp's version of this.