A method for monitoring an efficiency of a vessel during waterway navigation, the method comprising: - initially determining a reference efficiency term (EEOl r); - obtaining an efficiency indication (SEl i) corresponding to a time interval (Δt i) including: - acquiring an indication of a fuel consumption (FC i) by the vessel in the time interval; - acquiring an indication of a distance (D i) travelled by the vessel in the time interval; - calculating a current efficiency term (EEOI i) based on the indications of the fuel consumption (FC i) and the distance (D i) acquired for the time interval (Δt i); - acquiring an indication of fluctuation of a rudder angle during at least the time interval; - comparing the indication of fluctuation of the rudder angle against a first threshold value; - maintaining the reference efficiency term (EEOI r), if the indication of fluctuation of the rudder angle equals or exceeds the first threshold value; - overwriting the reference efficiency term with the current efficiency term (EEOI i), if the indication of fluctuation of the rudder angle remains below the first threshold value, and - calculating the efficiency indication (SEI i) including determining a ratio between the reference efficiency term (EEOI r) and the current efficiency term (EEOI i); wherein the method further comprises: - providing the efficiency indication to a display device. - initially determining a reference efficiency term (EEOl r); - obtaining an efficiency indication (SEl i) corresponding to a time interval (Δt i) including: - acquiring an indication of a fuel consumption (FC i) by the vessel in the time interval; - acquiring an indication of a distance (D i) travelled by the vessel in the time interval; - calculating a current efficiency term (EEOI i) based on the indications of the fuel consumption (FC i) and the distance (D i) acquired for the time interval (Δt i); - acquiring an indication of fluctuation of a rudder angle during at least the time interval; - comparing the indication of fluctuation of the rudder angle against a first threshold value; - maintaining the reference efficiency term (EEOI r), if the indication of fluctuation of the rudder angle equals or exceeds the first threshold value; - overwriting the reference efficiency term with the current efficiency term (EEOI i), if the indication of fluctuation of the rudder angle remains below the first threshold value, and - calculating the efficiency indication (SEI i) including determining a ratio between the reference efficiency term (EEOI r) and the current efficiency term (EEOI i); wherein the method further comprises: - acquiring an indication of a fuel consumption (FC i) by the vessel in the time interval; - acquiring an indication of a distance (D i) travelled by the vessel in the time interval; - calculating a current efficiency term (EEOI i) based on the indications of the fuel consumption (FC i) and the distance (D i) acquired for the time interval (Δt i); - acquiring an indication of fluctuation of a rudder angle during at least the time interval; - comparing the indication of fluctuation of the rudder angle against a first threshold value; - maintaining the reference efficiency term (EEOI r), if the indication of fluctuation of the rudder angle equals or exceeds the first threshold value; - overwriting the reference efficiency term with the current efficiency term (EEOI i), if the indication of fluctuation of the rudder angle remains below the first threshold value, and - calculating the efficiency indication (SEI i) including determining a ratio between the reference efficiency term (EEOI r) and the current efficiency term (EEOI i); - providing the efficiency indication to a display device.