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ECHO SOUNDER

Online study material for mates-Mariner Edition > Function 1 > Bridge Equipment > ECHO SOUNDER

Oral-Navigation (FUNCTION –1)

The following questions came from WhatsApp group where candidates posts the question right after they had finished their oral exam.
  • Should be capable of measuring UKC between 2 m and 200 m
  • Should provide minimum two range scale i.e. shallow range up to 20 m and deep range up to 200 m
  • The display should show at least 15 min of sounding
  • Should function properly when ship is rolling ±10° and/or pitching ±5°
  • Should function properly at ship speed from 0 to up to 30 knots
  • Speed of sound in water should be set at 1500 m/sec
  • The pulse repetition rate should be not slower than 36 pulses per minute for shallow range & not slower than 12 pulses per minute for deep range
  1. Stylus speed error:- The stylus is rotating with a certain constant speed and speed of the stylus is such that time taken by stylus to travel from top to bottom on the paper is exactly equal to time taken by sound waves to travel twice the distance of the range selected.
  2. Pythagoras error:- This error is found when dual transducer are used, one for transmission and one for reception. Due to the angle of beam, the measured depth is greater than actual depth.This error is calculated using Pythagoras principle.
    This error becomes more prominent, when distance between two transducer is more than 2 meters. In that case, manual should be referred in order to use the table for corrections.
  3. Multiple echoes:- Some strong echoes may bounce back and forth several times between ship’s hull and seabed, and hence providing multiple depth marks on the paper.
  4. Thermal and density layers:- Density of water varies with change in salinity and temperature of seawater which affect velocity of sound waves in seawater and cause error in depth recorded.
  5. Zero line adjustment error:- If the zero is not adjusted properly, it will give error in reading.
  6. Cross noise:- If sensitivity of amplifier is high, just after the zero marking, a narrow line along with several dots and dashes will appear. This is due to cross noise which occurs when small part of transmitted signal is picked up by receiver. This is controlled by swept gain control.
  7. Aeration:- When sound waves are reflected from air bubbles, it will appear as a dots on paper. This is known as aeration. This is due to pocket of air bubbles created during heavy weather, large alteration, pitching in ballast condition or astern propulsion.

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