ERRORS • Environmental factors can introduce errors in any system that relies for its operation on the transmission and reception of acoustic waves in salt water. • Errors in Transducer Orientation: The transducers should make a perfect angle of 60deg with respect to the keel or else the speed indicated will be inaccurate.
ERRORS • WATER CLARITY : • In exceptional cases the purity of the sea water may lead to insufficient scattering of the acoustic energy and prevent an adequate signal return. • 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.
ERRORS • AERATION : • 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. • Proper siting of the transducer, away from bow thrusters will reduce this error.
ERRORS • VESSEL TRIM AND LIST : • A change in the vessel’s trim from the calibrated normal will affect fore / aft speed and an excessive list will affect atwartship speed. • A JANNUS CONFIGURATION transducer reduces this error.
ERRORS • OCEAN CURRENT PROFILE : • This effect is prevelant in areas with strong tides or ocean currents. • In the water track mode, a speed log measures velocity to multiple layers several feet down in the water. • If these layers are moving in opposite directions to the surface water, an error will be introduced.
ERRORS • SEA STATE : • 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.
ERRORS • TEMPERATURE PROFILE : • The temperature of the sea water affects the velocity of the propogated acoustic wave. • Temperature sensors are included in the transducer to produce corrective data.
ERRORS • 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.
Side lobe Error • When the side lobe reception dominated over the main beam reception, there will be an error in the speed indicated. • 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. • The error can be reduced by reducing the beam of the transmitted acoustic wave.