Ranging and Phasing of EchoSounder

In an echo sounder the stylus is rotating with certain constant speed and transmission takes place when the stylus passes the zero mark.

When higher range scale is selected, the transmission will still take place when the stylus comes to zero. But the stylus speed is reduced because the stylus has to remain on the paper for longer period of time since the echos are returning from greater depths.

This system is known as “ RANGING “.

The range scales are generally provided as :

0 – 100 mtrs

0 – 200 mtrs

0 – 300 mtrs

0 – 400 mtrs

and so on.

Since the same length of paper now covers a larger depth the graduations become closer and it becomes difficult to read the depth accurately.

PHASING arrangement is used to avoid this.

In Phasing arrangement, the speed the stylus motor is kept constant, but the transmission point is advanced.

As shown in Fig, four sensors are positioned around the stylus belt and stylus is rotating at a constant speed.

A magnet mounted on the belt generates the pulse when it passes the sensor, which in turn activates the transmitter.

When the minimum range ( 0 – 100 mtrs ) is selected, the sensor 1 is used and the delay circuit arrangement is such that the transmission occurs exactly when the stylus passes the zero mark.

The bottom scale of the paper will depend on the speed of the stylus motor and it is set to 100 mtr.

On selecting the higher range ( 100 – 200 meters ), the sensor 2 is used for activating the transmitter and the zero of the scale so shifted that the top of the paper corresponds to 100 meters.

Since the speed of the stylus motor remains same, the bottom graduation corresponds to 200 mtrs.

Similarly, for measuring higher ranges different sensors are selected and the transmission time will be advanced accordingly.

It is always advisable to start the echo sounder at minimum range scale when phasing facility is provided, so that shallow depths are not missed.

Thus the danger of missing shallow waters can be avoided.






Autopilot-How it works?

The Autopilot is basically used when a ship has to steer a set course for a long time without alteration because any deviation from the set course is controlled electronically and automatically.

3 Types of controls:

a) —PROPORTIONAL CONTROL —The effect on steering when only proportional control is applied causes the rudder to move by an amount proportional to the off-course error from the course to steer and the ship will oscillate on either side of the required course-line.


—The rudder is shifted by an amount proportional to the rate of change of ship’s deviation from the course. The ship will make good a course which is parallel to the required course and will continue to do so until the autopilot is again caused to operate by external force acting on the ship.


—There are certain errors due to design parameters of the vessel which have to be corrected. Data signals are produced by continuously sensing heading error over a period of time and applying an appropriate degree of permanent helm is used for this purpose. The permanent helm acts as mid-ship.

—The output of these three controls is combined and the net resultant drives the rudder. This type of autopilot is also called as PID Auto Pilot.





The output from a gyro or magnetic compass is coupled to the comparator, in the control unit , along with the input signal from manual course setting control. Any difference between the two signals causes an output error signal whose magnitude is proportional to the difference between the two signals and hence the comparator is also referred to as proportional control. In addition to the proportional control, the control unit also consists of derivative and integral controls which analyse the signals from the gyro or magnetic compass and the course selector

—A summing amplifier is used to obtain a resultant error signal from these controls. This error signal is fed to the error amplifier which also gets feedback signals from the rudder, consisting of the rudder position and its movement. The output of this error amplifier is fed via telemotors to the steering gear unit and in turn operates the rudder. The telemotor has two units, i.e. Transmitter and Receiver situated on the bridge and steering gear compartment respectively. There will be no output from the control unit when the difference between the two signals is zero and hence no movement of the rudder results.







Difference Between AIS and LRIT

 AIS system does not communicate any globally available data, whereas LRIT is a globally available, satellite-supported system which meets the requirements of the authorities of having access to the data of individual ships globally and at any time. Time and frequency must be freely configurable by the authority requesting the data at all times. Manipulation by ships (e.g., entering incorrect data) must be eliminated.




  One of the most important differences between LRIT and AIS, however, is that AIS is a so-called broadcast system, i.e., is public, whereas LRIT data are only available to institutions which have a (governmental) entitlement to the data and guarantee the confidentiality of these data.

Another main difference is that  AIS is a Collision avoidance system mandated by the IMO whereas  LRIT is a Reporting system mandated by the IMO.