The words crewed, crude sound the same but have different meanings and spellings. Why do crewed, crude sound the same even though they are completely different words?
The answer is simple: crewed, crude are homophones of the English language.
Operated by an onboard crew: a crewed space flight.
Being in an unrefined or natural state; raw.
Lacking tact or taste; blunt or offensive: a crude, mannerless oaf; a crude remark.
Characterized by uncultured simplicity; lacking in sophistication or subtlety: had only a crude notion of how a computer works.
Not carefully or skillfully made; rough: a quick, crude sketch.
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.