Object compared: the she-camel’s long neck when it rises.
Comparison image: the rudder of an upriver boat on the Tigris.
Point of likeness: elongated form, elevated angle, and directed movement.
The prefix ka- in ka-sukkāni introduces the simile. Idhā ṣaʿʿadat bihi supplies its condition: the likeness is fully apparent when the camel raises her neck. That condition is central to the figure, not incidental decoration.