From the moment she stumbled off a dock and broke her back, Maureen McKinnon never really felt true despair. Paralyzed from the waist down, the 51-year-old from Marblehead, Massachusetts, was determined to carry on and find a competitive outlet. It took some searching, connections and coincidence, but eventually that outlet became high-level international sailing. She reached the pinnacle of the sport, winning a gold medal with Nick Scandone in the 2008 Paralympic Games. Now, eight years later, she is intensely focused on this year’s Games in Rio with helmsman Ryan Porteous, sailing the SKUD 18. In speaking engagements, her themes are empowerment, disability awareness and determination, which she says resonates with her audiences. “It’s an unsaid message of ‘I can do it with this wheelchair, as a single mother, skippers…