I've read that everything after the first four chapters is a major rewrite. I have the old edition and plan to get a copy of the new one - lots of changes in equipment, etc. since the first one came out.
I don’t have the 1st edition to compare to, but in his introduction Casey states:
"If you own the original...the first 5 chapters will seem familiar to you, but those you likely don’t need anyway. The stuff you do need has been completley rewritten... original topics extensively updated to reflect changes in technology, boating environment, and in my knowledge.”
1991 to 2008: I imagine there could be some updates!