We Constellation Marine Services as an independent survey company did performed or witnessed ship’s tanks soundings for various purposes and it is extremely important that to check the soundings of all bunker tanks in a ship in the presence of an independent surveyor (if appointed) during bunker intake or other related activities like on/off hire or ROB bunker survey.
The process of checking level of fluid in a bunker tank or other various tanks of ship is known as “sounding” of the tanks. From the sounding value of the tank, the total quantity of fluid (oil, bilge, sludge, or water) inside a ship’s tank can be easily determined with the help of certified calibration table. The initial process is to first measure the depth of the fluid from the surface to the bottom of the tank by using sounding tape.
Methods for taking sounding on a ship
ships are provided with sounding pipe through which a ship’s crew or surveyor can insert a sounding tape to measure the level in the tank manually. All bunker tanks on ship need to be gauged prior and after taking a parcel of any liquid bunker. Some of the most common gauging/sounding methods used on ship’s bunker tanks are:
a) Manual sounding
Manual sounding basically carried by using sounding tape which comes in meter or feet metric and is normally made up of brass and steel with a weighted bob attached at the end of the tape using a strap hook. If the fluid content inside a tank is more, usually free space of the tank (known as ullage) is measured which also can be converted into volume from the calibration table.
b) Electronic sounding Gauges
In electronic sounding, a sensor is used which senses the level of the fluid inside the tank or by sensing the tank pressure and sends a signal to the receiver. Here the signal is translated to the tank’s content value. The value is displayed using electrical operated servo gauge or electrical capacitance gauge.
Important points to be noted while sounding of ship’s bunker tanks
+ If the ship is rolling due to cargo operation or sea swell, surveyor need to check the sounding or ullage of tank at least 3 times and take average
+ Surveyor to check always the reference height of the tank and ensure that it is matching with calibration table. If any difference noted, add or minus the difference value to the measured sounding/ullage reading.
+ Apply correct oil finding paste to get clear oil cut especially for white oils
+ Surveyor to verify the condition of sounding tape by comparing with surveyor’s own measuring tape or ruler and be aware using wrong size of bobs. Always use a ruler to check exact sounding especially if it is below 20 cm.
+ Surveyor to ensure the battery is fully charged if sounding is carrying with electronic devices
+ Always wear appropriate PPE