The words y'all, yawl sound the same but have different meanings and spellings. Why do y'all, yawl sound the same even though they are completely different words?
The answer is simple: y'all, yawl are homophones of the English language.
Chiefly Southern U.S. Variant of you-all. See Regional Note at you-all.
A two-masted fore-and-aft-rigged sailing vessel similar to the ketch but having a smaller jigger- or mizzenmast stepped abaft the rudder. Also called dandy.
A ship's small boat, crewed by rowers.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.