A well-known man in the blue water area,  Frederick Moore, passed away yesterday (Thursday) morning at the age of 74.  Moore was the former chairman of Diamond Crystal Salt in St. Clair and DSLT Inc.   He was also known as a community activist, real estate developer and philanthropist.  The Diamond Crystal Salt Company in St. Clair was founded in 1886 by his great-grandfather.  Moore was appointed chairman of the board in 1982, leading the company through the sale of its sale division to the International Salt Company in 1988.  Mr. Moore also stared Diamond Boat Works of Fort Gratiot with a partner in 1989.  The company, which is now located in Lexington restores vintage boats and motors.  He was also involved in MainStreet Port Huron and was a recipient of the Spirit of Port Huron Economic Progress award.  Moore was active in a number of local boards and committees.  Funeral arrangements have not yet been completed.