Fellow senior Jack Benoit won the 100 backstroke for Greely, and also contributed to a relay win in the 200 medley with Griffin Fluet, Connor Russell and Dunnett.
Morse High School (263 points) placed second, 26 points back.
Cape Elizabeth (196) edged Camden Hills and Mt. Desert Island by one for third in the 26-team meet, which was contested with times heats rather than the traditional consolation/finals format in order to beat another round of snow.
Dunnett was named performer of the meet. He earned victories in the 200 individual medley, and in the 100 butterfly.
Michael Dempski was the lone swimmer to place in his event Tuesday at the Class B swimming and diving championships for Saint Dominic Academy, finishing 16th in the 100-yard butterfly at Bowdoin College.
Dempski’s time of 1:03.51 topped Burke Riley of Hyde for the final scoring position.