At the Connecticut Long Course Junior Swimming Championship in New London on July 15, 1971, swimming for the Stamford, Connecticut Dolphins Swim Club, Sinnott demonstrated diverse stroke skills, swimming a 1:07.9 for the Boys' 110-yard
backstroke, and a 2:28.0 in the 220-yard medley in the 15–17 age group. By 1972, he had distinguished himself as a High School All American, placing third in the 200 freestyle at the AAU Metropolitan Championships in Roslyn, Long Island in July, 1972. In the summer Sinnott played softball, and was a very capable hitter, knocking in 17 runs while hitting three home runs as a sixteen year old in the Saugerties Softball League playoffs. Helping his Stamford Dolphins Swim Club win the meet on points, Sinnott won both the 400 freestyle and the 200 Individual Medley at the Region 1 AAU Long Course Swimming Championships in
Princeton, New Jersey on July 21, 1970. By winning the regional meet, the Dolphins and Sinnott advanced to the Eastern Championships. Again swimming for the Dolphin Swim Club of Stamford, Connecticut, Sinnott placed third in the 400-meter individual medley at the Eastern
USA Swimming Championships on August 7, 1971. == Swimming for SMU ==