To both of you, I'd love to exchange ideas on teaching blind swimmers as I've been coaching two for several years. I've completed the Chesapeake myself, and guided my blind friend Mark Rew twice in their 1-mile event, and in 2016 we did a 3K OW. I'm gathering my experiences and ideas together for a book to help those of us with blind friends who want to swim better. I documented some of the experience in a forum string here.
The only blind swimmer I'm aware of who completed the GCBS so far is the absolutely awesome Triple Crown and Hall of Fame swimmer James Pittar of Australia who was guided by a kayaker using a whistle to give "right/left" directions.