ERRORS n Environmental factors can introduce errors in

ERRORS n Environmental factors can introduce errors in any system that relies for its operation on the transmission and reception of acoustic waves in salt water. n Errors in Transducer Orientation: The transducers should make a perfect angle of 60 deg with respect to the keel or else the speed indicated will be 1

ERRORS WATER CLARITY : n In exceptional cases the purity of the sea water may lead to insufficient scattering of the acoustic energy and prevent an adequate signal return. n It is not likely to be a significant factor because most sea water holds the suspended and micro organisms that adequately scatter an acoustic beam. n 2

ERRORS AERATION : n Aerated water bubbles beneath the transducer face may reflect acoustic energy of sufficient strength to be interpreted erroneously as sea bottom returns producing inaccurate depth indications and reduced speed accuracy. n Proper siting of the transducer, away from bow thrusters will reduce this error. n 3

ERRORS n VESSEL TRIM AND LIST : n A change in the vessel’s trim from the calibrated normal will affect fore / aft speed an excessive list will affect atwartship speed. n A JANNUS CONFIGURATION transducer reduces this error. 4

ERRORS OCEAN CURRENT PROFILE : n This effect is prevelant in areas with strong tides or ocean currents. n In the water track mode, a speed log measures velocity to multiple layers several feet down in the water. n If these layers are moving in opposite directions to the surface water, an error will be introduced. n 5

ERRORS n SEA STATE : n Following seas may result in a change in the speed indication in the fore-aft and port-stbd line depending upon the approaching sea relative to the ship’s axis. 6

ERRORS n TEMPERATURE PROFILE : n The temperature of the sea water affects the velocity of the propogated acoustic wave. n Temperature sensors are included in the transducer to produce corrective data. 7

ERRORS n n n PITCH & TRIM : Varying angles of pitch or trim from the horizontal introduce a small error factor. This error cannot be corrected, however such errors are negligible. The problem of heaving (vertical acceleration ) can be significant causing an additional error factor. This factor can be cancelled out by using JANNUS CONFIGURATION. 8

Side lobe Error When the side lobe reception dominated over the main beam reception, there will be an error in the speed indicated. n This error is more pronounced on a sloppy bottom, where the side lobe will be reflected at a more favorable angle and will have path lengths less than the main beam. n The error can be reduced by reducing the beam of the transmitted acoustic wave. n 9