SATURDAY was a special anniversary for three Southampton men - Mr. Walter Hurst of 5 Granville Street, Mr. Leo James Hyland of 11 Burlington Road, and Mr. George Kemish of 14 Begonia Road. Exactly 46 years ago these three were part of the crew aboard the Titanic, up to that time the greatest luxury ship ever known, the night it sank in mid-Atlantic on its maiden voyage. Struck by an iceberg, 300ft of its underbelly was ripped out and the ship, which had been called ''unsinkable'' went down with a total loss of 1,503 lives.