Looking in more detail at the route map would suggest that you are right Perryman. Although the canal follows the line of Davids Road if the map is correct it was actually located between Davids Road and Havelock Walk so the wall outside the Hob would be on the wrong side and the ramp couldn't lead to the water.

A shame if that is so because I always liked to think that was a little bit of history that had survived!