After conducting an online search, I was unable to find specific information regarding the boat ramp named Highway 76 4770 located in Brownsville, Tennessee. However, based on general knowledge of boat ramps, it can be assumed that it is a public access point to a body of water for launching boats.

The width of the boat ramp is unknown without further information or local knowledge. The size of boat ramps can vary, but they are typically wide enough to accommodate the launching and retrieval of boats.

Without knowing the specific body of water the boat ramp services, it is impossible to determine what kinds of watercraft are permitted. Different bodies of water may have varying regulations for the types of boats allowed on the water, such as restrictions on motor size or hull length.

In order to obtain accurate information about the Highway 76 4770 boat ramp, it is recommended to contact the local authorities or the Tennessee Wildlife Resources Agency for further details.