Echo Sounder Flashcards
What is the principle of an echo sounder?
To measure the time taken for a pulse to travel from the ship to the bottom of the seabed and back.
What’s the equation ?
Range = speed x time / 2.
Speed is known as 1500m/s.
Echo sounds record depths from?
2m to 400m
When setting up a echo sounder, what 4 things are you going to consider.
Alarms
Gain (sensitivity)
Discriminator
Datum
Why do you set up alarms on echo sounder when setting up?
Set alarms that are preset to warn of depths less then expected.
Why set up the gain when setting up the echo sounder?
It controls the receiver sensitivity.
Must be set correctly for accurate results.
Why set up the discriminator?
Shortens pulse length.
Helps distinguish bottom returns from noise and fish etc.
Why set up the datum?
Echo sounder a allow offset correction therefore sounder shows DBK for safety.
DBS?
Depth below surface. Relies on correct draft.
DBT?
Depth below transducer. Warns when likely to run aground.
Name 3 echo sounder errors
Index error
-due to faulty offset correction.
Separation error
-reciever and transducer fitted, the horizontal distance between them causes an error in depth.
Second trace returns
-in deep water.
-echo from one transmission may be received after the next has been sent therefore indicated depth will be shallower than the true depth.
Name 3 propagation effects:
-Aeration **
Bow waves cause AIR BUBBLES under hull 1/4 length fwd and 1/4 length aft. Blocking signals.
Reversing propellas have same effect
also high speed aggravates it.
-propagation speed error**
Readings less in hot saline seas then in cool fresh water.
-water layers of differing salinity/ density/ temperature.
Name some false echoes
-Multiple echos (may bounce number of times between sea bed and surface/hull.
Cone effect
Side echoes
Fish shoals
Fresh water springs
Kelp
Turbulence from other ships wash.
