10-3
1 Introduction
1.1 Basic Functional Description
WATER TRACK U is an electronic Speed and Distance Measuring Equipment board designed
to be used in JLN-900 Speed Log. To create a working log the WATER TRACK U docks to a
motherboard within the Sig.Processor where the measuring sensor (transducer), speed
indicators and optional repeaters are also connected. The signals from the transducer are
processed within the WATER TRACK U and the result can be read from
IEC 61162/NMEA telegram syntax and how to connect cables carrying IEC 61162-serial
signals are described in document Section 11.
The speed-log works technically like two small, synchronized echo sounders built together,
comparing echoes from water particles close to the hull. The calculation is based on cross-
correlation, a mathematical method to estimate the similarity of two waveforms (described
below), which entails that it is very dependable and reliable in all kinds of waters. Logs based
on WATER TRACK U has no moving parts and no parts extending below the hull of the ship.
1.2 Definitions and abbreviations
Abbreviation Description
Sig.Processor Main Unit JLN-900 Speed Log
NMEA0183 IEC 61162-1 serial interface standard
JLN-900 Speed
Log
Combined SOG and STW log.
STW Speed Through the Water.
This is equivalent to Water Track (WT) speed (relative)
SOG Speed Over the Ground.
This is equivalent to Bottom Track (BT) speed (true)
TRU Transducer
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