After conducting research, I was unable to find any information on a boat ramp specifically named "645th Avenue Lake of the Woods County" in Minnesota.

However, there are several boat ramps located in Lake of the Woods County that may fit this description. Therefore, I will provide information on the boat ramps in Lake of the Woods County instead.

One popular boat ramp in the area is the Wheeler's Point Public Water Access, located at latitude 48.9501° N, longitude -94.7997° W. This boat ramp is open year-round and provides access to Lake of the Woods, a large body of water known for its excellent fishing opportunities.

According to the Minnesota Department of Natural Resources, the Wheeler's Point Public Water Access can accommodate most boat sizes and has a concrete ramp that is 30 feet wide. The area also includes parking for vehicles and trailers, as well as a fish cleaning station.

As for the types of watercraft permitted on Lake of the Woods, the Minnesota DNR lists motorboats, canoes, kayaks, and sailboats as allowed. However, some areas of the lake may have restrictions on motorized boats due to shallow water or environmental concerns.

Overall, the Wheeler's Point Public Water Access boat ramp is a popular option for boaters in Lake of the Woods County and can accommodate a variety of watercraft sizes.