The Wissler, one of the club’s major trophies is a match play knockout competition played through the summer season.
To reach the final Dunn and Beecroft had to beat several pairs, including past champions Shaun Smith and Kevin Henman.
In the final they beat Dale Corcoran and Nick Hudson with the match ending on the 17th hole.
The Wissler Trophy has been won several times by father and son combinations but this is the first time it has been won by a grandfather/grandson pairing.
Dunn, who played over 900 matches for Scarborough Football Club, said “Josh has played really well through the summer and is now playing off three handicap.
“To win a top trophy playing with my grandson feels very special.”