Patent ID: 7483336

Claim:
An avoidance device for a ship, allowing said ship to avoid floating or slightly submerged objects situated on a route of the ship or in a zone close to said route, comprising: two transmitters of acoustic waves spaced apart from one another; an acoustic receiver, whose reception band is suitable for the transmission frequencies of the transmitters, said receiver being configured to receive echoes resulting from the reflection of the signals transmitted by each of the transmitters; means of processing of the received signals, said processing means performing, from the echoes received, a measurement of the difference of the propagation times of the waves transmitted by each of the transmitters after reflection of the waves by an object as well as a measurement of the Doppler effect which affects each of the transmitted waves; said processing means implementing a process for determining the position of said object comprising the two following stages; a first stage, during which a coarse determination of the position of the object is carried out by calculation of the difference (T 2 -T 1 ) of the propagation times of the waves; a second stage during which the position of the object is determined in a more precise manner by calculation of the differential Doppler frequency Δf d of the waves from the frequencies F 1 and F 2 transmitted by the transmitters, and from the frequencies Fr 1 and Fr 2 received by the receiver, said differential Doppler frequency Δf d being defined by the following relation; Δ f d =ΔFr−ΔF wherein Δ Fr=Fr 2 −Fr 1 and Δ F=F 2 −F 1 .