the longboat was pulled up very tight to the side of the canal , the ropes that secured it fore and aft wound numerous times around their mooring poles allowing no slack for the vessel to drift , and so with no gap between the path and the sides of the boat rob was able to silently edge himself along the barges flank , hand-over-hand like a mime artist imitating coming up against a brick wall , until he was able to peer in the corner of the small porthole .