Errors of Echo Sounder Working /Bridge Equipment

In this Video we are going to learn about Echo sounder :
What is an echo sounder?
Why is sound used in ES?
Brief History
Principle of operation of an ES using a block diagram.
Settings on an ES.
Errors of ES
Echo Reflected Sound
To Sound To gauge depth.
The echo sounder is a device used to measure the under keel clearance or the depth of water under the ships keel
Sound is the most efficient medium for underwater work.
Other forms, e.g. electromagnetic or light radiation attenuates rapidly and are therefore have limited use.
Two common equipment used by a mariner are
Echo sounder to measure depth of water
Doppler log to measure speed.
In 1912, sound was first used by German Scientist Alexander Behm to detect icebergs .
It failed but proved useful to measure depth of sea.
Application of echo-sounding principles for submarine detection during World War II.
The main line of defence for the USA against Enemy nuclear submarines with nukes.
1960 onwards great advancement in using sound to detect fish at sea.
Currently the only technology to measure depth of water at sea and which is unlikely to be replaced by anything
Principle of operation of an ES :
ES works on the principle of reflection of acoustic energy.
Short pulse of sound energy is transmitted vertically down from the ship.
This pulse travels towards the sea bottom and after hitting it, is reflected back to the ship.
Main Components :
The Recorder
The Pulse Generator
Transmitter
Transducer
Receiver
Amplifier
A common paper echo-sounding recorder consists of an arm with a stylus on the end rotating quickly across a slow moving electro-sensitive paper.
As the pulse travels to the bottom and returns, the stylus moves a proportional distance at half the speed of sound across the paper, and on detection of an echo, again marks the paper thus indicating the depth.
Why half? Because the stylus has to represent the to and fro journey of the transmitted pulse.
As the paper is also continuously moving a profile of the sea bed can be seen, thereby satisfying the IMO requirement of maintaining record of past depths.
Sequence of Working :
A pulse from the Pulse Generator activates the transmitter which sends a powerful electric Pulse to the Transducer.
The transducer converts the electric energy into sound energy producing a sound pulse .The sound energy travels to the bottom, hits the bottom and gets reflected back to the transducer.
The transducer converts the received sound energy back to an electric pulse and sends it to the receiver.
In the receiver the received signal is processed, amplified and sent to the Recorder.
At the recorder, the stylus which has been moving at a speed proportional to half the speed of sound, creates a physical mark on a paper
On a digital display, a blip will be shown.
Transducer :
A Transducer is a special magneto-striction device which converts transmitted electrical energy into sound energy and the returned sound energy into an emf.
Magneto-striction effect occurs in all ferromagnetic material, but particularly pronounced in iron, nickel and cobalt.
Ferro-magnetic material change their length when an emf is applied. Conversely, when subjected to physical stress they generate an emf.
In an ES, an alternating current is used to create a magnetic flux, which will vibrate the transducer and create a a sound pulse.
Conversely, when a sound pule hits a tranducer , an emf will be created between the ends of the Tranducer.
Errors of Echo Sounder :
Draught Error
Stylus speed Error
Transmission Error
Velocity Error
Pythagoras Error
Beam Width
The system measures the depth under the transducers.
To convert this to actual depth of water, the depth of transducers must be added.
Most systems have a zero adjustment, which can be used to allow for this.
Many navigators however, prefer the display to indicate “clearance” rather than “depth”
Stylus Speed Error
Is the result of the stylus not moving at the appropriate speed for the range scale in use.
Transmission Error
Is the result of the stylus not being at the zero on the scale (or at correct draught) when the pulse is fired.
Velocity Error :
Most systems are calibrated using a propagation velocity of 1500 m/s.
If the actual velocity is different, the depth indicated will not be accurate.
Lower velocities (like 1430 m/s in FW) will give higher reading which is dangerous. Why?
Sound in FW will travel at lower speeds.
It will take longer for travel to bottom and back.
ES will multiply this time with higher velocity settings and give higher than actual depth.
In the red sea, readings are 5% low due to increased temperature and salinity. Echo sounding correction tables together with chart 5330 contain appropriated corrections.
Pythagoras Error on Echo sounder :
Spurious Echoes :
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