Marine Echo Sounder

Summary

This video delves into the evolution of depth measurement at sea, from traditional methods like the lead line to modern echo sounders. It explains how echo sounders work using the principle of sound wave transmission and reception to calculate depth, with a focus on the importance of accurate settings for transducers and understanding potential errors such as speed of sound variations and multiple echoes. The tutorial also covers practical aspects like setting alarms and adjusting for safety margins.

Takeaways

• 📣 Echo sounders are used to measure the depth of water, replacing the old method of using a 'deadline' with a rope and weight.
• 💡 The echo sounder operates on the principle of sonar, sending out a pulse and measuring the time for the echo to return.
• 🔍 The depth is calculated by multiplying the time taken for the echo to return by the speed of sound in water (approximately 1500 meters per second) and dividing by 2, as the sound travels to the seabed and back.
• 🛠️ Modern echo sounders offer features like digital readouts, adjustable parameters, and the ability to display depth in different units (meters, feet, fathoms).
• 📊 The display can show the depth as an absolute value or a value adjusted for the vessel's draft plus an offset for safety.
• 🚨 It's important to set the correct range on the echo sounder to match the average depth in the area to avoid incorrect depth readings.
• 🌡️ The speed of sound in water can vary with temperature and salinity, affecting the accuracy of depth measurements.
• 📏 The Pythagorean effect can cause errors in depth readings on vessels with a significant beam angle, as the sound travels further before reflecting off the seabed.
• 🕒 Second trace echoes can occur when the seabed is soft and the sound waves are slow to return, potentially showing a shallower depth than is actually present.
• 🎶 Multiple echoes can result from a rocky seabed causing the sound waves to bounce back several times, leading to multiple depth readings at the same location.
• 💥 Echo sounders can also be affected by bubbles or cavitation, which can cause errors in depth measurement.

Q & A

What was the traditional method used to measure the depth of the sea in the olden days?

In the olden days, a method called 'lead line' was used. It involved a sticky paste called 'lead' in a line, which was thrown overboard to the seabed. The depth was determined by the amount of line paid out.

What is an echo sounder and how does it work?

An echo sounder is a device that measures the depth of the water by emitting a sound pulse and measuring the time it takes for the echo to return. It uses the principle of echo ranging, where the time taken for the pulse to travel to the seabed and back is used to calculate the depth.

How is the depth calculated using an echo sounder?

The depth is calculated by multiplying the time taken for the echo to return by the speed of sound in water (approximately 1500 meters per second) and then dividing by 2, since the sound travels to the seabed and back.

What is the average speed of sound in water according to the script?

The average speed of sound in water is 1500 meters per second.

What is the purpose of the digital readout on an echo sounder?

The digital readout on an echo sounder provides a numerical display of the depth below the transducer in meters.

What is the significance of the 'actual' setting on an echo sounder?

The 'actual' setting on an echo sounder is used to display the real-time depth, as opposed to the 'record' setting, which shows the history of depths.

How can the range of the echo sounder be adjusted?

The range of the echo sounder can be adjusted by using the 'range' button, which allows the user to match the display range with the average depth in the area.

Why is it important to use the correct scale on an echo sounder?

Using the correct scale is important because if the wrong scale is used, the depth values will be incorrect.

What does the 'draft' setting on an echo sounder represent?

The 'draft' setting on an echo sounder adds the draft (the depth of a ship's keel below the waterline) to the depth reading, providing a more accurate measurement of the minimum depth required for safe navigation.

What are some of the errors associated with echo sounders?

Errors associated with echo sounders include changes in the speed of sound due to water temperature and salinity, the Pythagorean error due to the angle of the transducer, second trace echoes from soft seabeds, multiple echoes from rocky bottoms, and shallow water effects.

How can the speed of sound in water affect the accuracy of an echo sounder?

The speed of sound in water can affect the accuracy of an echo sounder because changes in temperature and salinity alter the speed of sound. If the echo sounder does not account for these changes, it may display incorrect depth readings.