Because the Alden oars have a square shaft, rounded bottom oarlocks wouldn't work. Traditional sculling oars are square but they used a light-weight gated oarlock which Arthur didn't like because it was too complex and not hardy enough for the Aldens. He wanted an oarlock design that was simple to use but very dependable in managing the long stroke of the 9'-9" oars.
Douglas Martin quickly went to work on this problem and carved a wooden prototype the very same day.
Known as the Douglas Oarlock, this simple yet elegant solution continues to be sought after almost 30 years later.