Patent ID: 7417924

Claim:
An apparatus comprising: (a) at least two vessel hull-mounted transmitters, each positioned on the under side of the vessel hull, or bulb of the hull, the transmitters stationed on members a known distance from a known vessel reference point and adapted to generate a spread spectrum signal having an orthogonally encoded signal sequence; (b) a plurality of acoustic receivers adapted to be along or in one or more cables, the cable adapted to be in or traversing through the fluid with a vertical component, each receiver adapted to receive at least the spread spectrum signals; and (c) a calculation unit adapted to cross-correlate the spread spectrum signals detected by the receivers with the orthogonally encoded signal sequence of the spread spectrum signals, and adapted to use measured time differences between detection of the spread spectrum signals at each receiver and measure differences in arrival time between signals from different transmitters to each receiver, to calculate distances between the receivers.