Sounding and Ullage explained for dummies

Sounding-Is the measured height (in meters) from the bottom of the tank to the liquid surface.

Ullage-Is the measured height (in metre) from the liquid surface to the top of the tank or sounding pipe.

A simplified diagram to better explain these two concepts.

Manual procedure to take a sounding using sounding tape 

1. Open the cap of sounding pipe 
2. Lower the sounding tape lower the bob until it touches the bottom (the striker plate)
3. Heave up the sounding tape and note the height of the liquid on the tape

Other methods to take Sounding onboard

1. A mechanical sounding gauges-Provision such as float gives the corresponding quantity of tank attached to a point through a pulley
2. Bubber gauge-uses the principle fo hydrostatic pressure to give the liquid level
3. Differential pressure guage-Uses the difference between two pressure points within a process system to give the level
4. Electronic sounding gauge-Senses the pressure inside the sounding pipe or the tank and sends the signal  to a receiver.signal is translated using a PLC circuit and the value of the liquid level is determined
5. Ultrasonic sounding gauge-Uses principle of echo sounder by throwing an ultrasonic wave from the gauge and is being detected by a sensor, routes it through a microprocessor and provides a digital value for the sounding or level of liquid

Manual procedure to take an Ullage using Sounding Tape 

1. Open the cap of sounding pipe 
2. Find out the depth of the sounding pipe and note the value
3. Lower the sounding tape until the bob touched the liquid surface, this can be felt by feeling the resistance, note the height of the tape let go 
4. Heave up the sounding tape and note the height of the liquid on the tape(measured value)   

Ullage=Height of tape let go ーHeight of the liquid on tape

Sounding=Depth of sounding pipeーUllage

Example1: If 1.64m is the depth of the sounding pipe and the height of the tape let go is 1m  and the height of the liquid measured on the tape is 0.14m

Then 

Using the above mention methods and formula

• Ullage=1.0ー0.14=0.86m
• Sounding=1.64ー0.86=0.78m

UTI Gauges

UTI's are heavily used in tankers by the chief officers for accurate cargo calculation, used to primarily gives 3 parameters or data.

• Oil level -ullages
• Oil-water interface
• Temperature

Different maker have different designs and models, to ensure they remain correct in measurement,UTI's are calibrated ones every year by specialist

Practical tip for accurate Sounding/Ullage

• Use genuine and high-quality tapes.
• Clean and maintain the sounding tape regularly.
• Sounding tapes to be cleaned and stowed in a bucket after use.
• Use appropriate paste ie, water finding paste or oil finding paste.
• Consider the effect of trim and list of the ship.
• For accuracy take sounding when vessel at relative calm conditions.