Būṣiyy names a kind of boat, and Dijlah is the River Tigris. Muṣʿid presents the vessel travelling upward, against the current or toward the upper reaches. Sukkān is the component used for steering its direction.
This riverine image broadens the imagery of a desert poem. It is the upright, angled steering apparatus of an advancing boat that illuminates the lifted neck. Reducing sukkān to a generic paddle can obscure the more specific visual resemblance.