After conducting research, it appears that there is a boat ramp named Williamsburg County in South Carolina. This boat ramp is located at latitude 33.49481964 and longitude -79.96054077.

According to the South Carolina Department of Natural Resources, the Williamsburg County boat ramp is a freshwater boat ramp that services the Black River. The Black River is a 150-mile-long river located in the eastern part of South Carolina. It is known for its scenic beauty and is a popular destination for boaters, fishermen, and kayakers.

As for the size of the boat ramp, there is no specific information available on its width. However, it is described as a "moderately sized" boat ramp that can accommodate a range of watercraft.

In terms of the types of watercraft permitted on the Black River, it appears that there are no restrictions. However, boaters are encouraged to follow all safety guidelines and regulations set forth by the South Carolina Department of Natural Resources.

In conclusion, the Williamsburg County boat ramp in South Carolina is a freshwater boat ramp that services the Black River. It is described as being moderately sized and can accommodate a range of watercraft. There are no restrictions on the types of watercraft allowed on the Black River, but boaters should follow all safety guidelines and regulations.