It's a pretty long walk, if they're talking about walking to Great Bay Beach, which would seem to me to be the closest one to the ship. It's about a 10 minute cab ride, so maybe a half-hour walk. Maybe I just remember it being further than it actually is. I do know it's never occurred to me to walk, and I walk everywhere.
They easiest way, in my opinion, is to take the water taxi. It's $5 for the day for unlimited trips. It leaves from the foot of the cruise ship pier and will drop you off right at the beach.