وَأَتْلَعُ نَهَّاضٌ إِذَا صَعَّدَتْ بِهِ
كَسُكَّانِ بُوصِيٍّ بِدِجْلَةَ مُصْعِدِ
Her tall, readily lifting neck, when she raises it, resembles the rudder or steering projection of a boat making its way upstream on the Tigris.
Atlaʿ describes a long, high neck; nahhāḍ emphasizes its capacity to rise. Sukkān būṣiyy is the rudder or steering member of a type of boat.
The resemblance concerns more than length: elevation, angle, and purposeful movement make the boat’s steering projection an effective comparison.