START ROCKAWAY BOARDWALK UNIT Borough President George U. Harvey of Queens held a rope which guided a heavy timber pile into place on the ocean beach at the foot of 86th st., Edgemere, Queens, yesterday, and work on the third section of the Rockaway boardwalk officially commenced. The section will cost $61,240, is to be 40 feet wide, and will run from Beach 56th st. to Beach 21st st.