Port dagger board and spring gone after broad sided by 6' bow wave of 'Contrarian', a 70' super yacht. This was on top of 2-3' chop in the harbor. She crossed me within 50-75 yards under heavy air -20-25knts. I was knocked of the boat, bruized and shaken. I approached the captian later that day at the marina and he accepted reponsibility for his actions($315).