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Echo sounder — Navigation B — Instruments, Mashit 30

14 questions on echo sounder, from the Navigation B — Instruments exam of Mashit 30. The transducer, its care and comparing the sounding with the chart. Every question is shown with its correct answer, as in the official question pool.

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Questions on Echo sounder

  1. What is an echo sounder used for? Safety at sea, navigation, route planning and anchoring.
  2. Where is the echo-sounder transducer fitted? The depth at which it is fitted does not matter, because the display can be adjusted to show depths from the deepest point of the draught; but the beam must not be disturbed by bubbles or nearby objects.
  3. How should you look after the echo-sounder transducer? Gently remove weed and marine growth from it (not with a metal tool).
  4. How should you look after the echo-sounder transducer? Paint it with a paint that contains no metal.
  5. When would you use the echo sounder? For safety at sea, navigation and anchoring.
  6. While underway, the echo sounder shows a depth of 12 metres, while the chart shows 10 metres at the same place. The vessel's draught is 1.2 metres. What causes the difference? The chart gives depths at the lowest low water, and at the time of the sounding the height of tide is 3.2 metres.
  7. Which of these does not affect the accuracy of an echo sounder? The electric field created by the friction of the rudder against the surface layer of the water.
  8. The echo sounder shows a depth of 10 metres, your vessel's draught is 2 metres and the height of tide is 1 metre. What depth should the chart show? 11 metres.
  9. While underway, the echo sounder shows a depth of 12 metres, while the chart shows 10.8 metres at the same place. The vessel's draught is 1.2 metres. The difference arises because: The chart gives depths at the lowest low water, and at the time of the sounding the height of tide is 2.4 metres.
  10. If there is no echo sounder, or it is not working, how else can you estimate the depth? Choose the most practical answer: For small depths, use a line with a weight on it; for greater depths, read and work out the depth from the chart's figures and symbols, allowing for high and low water.
  11. When you increase the depth range on an echo sounder: Fewer pulses are transmitted per unit of time.
  12. What is the function of the transducer in an echo sounder? To convert the electrical (radio-frequency) pulses into sound waves when transmitting, and to convert the returning echo back into an electrical signal when receiving.
  13. How should you look after the echo-sounder transducer? If it is an oil-filled ceramic type, check the oil level and top it up if needed.
  14. Assume the echo sounder shows the depth below the deepest point of the hull. A vessel with a draught of 1.5 metres measures a depth of 1 metre, while the chart shows 2 metres. What is the reason for the difference? The chart depth is given for the lowest low water, but at the time of measurement the tide is 0.5 metres above the charted level.

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