A circular casing enclosing the propeller. The propeller operates with a small gap between blade tips and the nozzle internal wall, roughly at the narrowest point. The nozzle ring has a cross-section shaped like a hydrofoil. The nozzle increases the thrust at low speeds. The Wärtsilä high efficiency nozzle increases bollard thrust up to 30% at low vessel speeds. Tugs, fishing vessels, dredgers, and inland waterway vessels, which typically have heavily loaded propellers, will gain more thrust under these demanding conditions. Some types of general cargo vessels with relatively low sailing speeds might also benefit from installing a nozzle.