If it's the Queensferry near Edinburgh i can't find a BOAT marked on the map. Are you sure it's a BOAT or could it be just an unclassified road? Green Lanes are usually BOAT's (Byways Open to All Traffic) ....
If it's the Queensferry near Connahs Quay in Flint then again I can't find one anywhere near that name .. there is a BOAT marked across the river Dee called Kingswood Lane .. and a few small ones at Ewloe/Burntwood/Drury but I can't find any others.
Lots of interesting looking unclassifieds around the area and further out towards Mold etc, but nothing close to the name you gave ..
I think you need to be a little more specific.