According to USCG's suggestion, it requests different dock line diameter to different boat size.Amarine Made has different sizes of different colors of double braided dock lines.
For boat length under 20 feet,dock line dia should be 3/8 inch;
For boat length from 20 to 30 feet,dock line dia should be 1/2 inch;
For boat length from 30 to 40 feet,dock line dia should be 5/8 inch;
For boat length from 40 to 46 feet,dock line dia should be 3/4 inch;
For boat length from 55 to 63 feet,dock line dia should be 7/8 inch;
For boat length from 64 to 72 feet,dock line dia should be 1 inch.