After conducting research, I was unable to find a boat ramp named Beach Avenue in Whatcom County, Washington with the given latitude and longitude coordinates. Therefore, I cannot provide accurate information about the ramp's width, the body of water it services, or the types of boats allowed to launch from it.

It's possible that the name or location of the boat ramp may have changed, or that the coordinates provided are incorrect. Without further information, I am unable to provide a detailed description of the boat ramp.