Pre-swirl stator

A pre-swirl stator is an energy-saving device fitted just ahead of the propeller, a set of fixed vanes on the hull or stern boss that imparts a swirl to the inflow opposite to the propeller’s rotation. The pre-rotation lets the propeller recover rotational energy that would otherwise be lost in the slipstream, raising propulsive efficiency and cutting fuel consumption by a few percent. It is one of the wake-equalizing and flow-conditioning devices counted toward EEXI and EEDI improvement under MARPOL Annex VI. Unlike a post-swirl device such as rudder-bulb fins, the stator works on the flow before it reaches the disc, and it has no moving parts.