No 8 Pontoon was at Smith's Dock, North Shields and it was a floating dock with one side. The "high" side of the pontoon was attached to the river bank by a jointed arm that allowed the pontoon to rise and fall but not move in any other direction.
See:
viewtopic.php?f=147&t=14527viewtopic.php?f=147&t=14525viewtopic.php?f=219&t=12889&p=30885#p30885So presumably the AMBLE was about to be docked, but I don't know when.
EDIT: Having now seen the later photos, the AMBLE was docked on the 20/09/1938