1.10 Level Measuring Device and Technique

Level measuring devices are essential tools used on ships to monitor and control the levels of various fluids such as fuel, oil, water, and other liquids in tanks and systems. Understanding these devices is crucial for maintaining the safe and efficient operation of the ship's engine room. As an engine cadet, you will encounter these devices frequently during your duties, and a clear understanding of how they work and how to use them will be a key part of your training.

Why Level Measurement is Important?

Level measurement plays a critical role in maintaining the balance and stability of the vessel. It ensures that fuel and lubricating oil levels are within the safe operating range, helps prevent overflow and spillage, and aids in the efficient management of ballast water and bilge systems. Proper level monitoring is essential for avoiding engine failure, environmental incidents, and ensuring the safety of the ship and crew.

Techniques for Level Measurement

Level measurement can be direct (sight glasses and floats) or indirect (using sensors and transmitters). Each technique has its advantages and limitations, depending on the type of fluid, tank configuration, and environmental conditions.

Manual Measurement: In some cases, manual sounding rods or tapes are used to measure levels. Although less common on modern vessels, this technique is a reliable backup method.
Automated Systems: Most modern ships are equipped with automated level measuring systems that continuously monitor fluid levels and display the data on control panels. These systems can also trigger alarms if levels are outside safe ranges.

Manual measuring tools

For manual level measurement on board ships, especially in engine rooms and tanks, several traditional measuring tools are commonly used.

1. Sounding Tape (Dip Tape)

Description: A calibrated steel or fiberglass tape with a weight (bob) at the end, used for measuring the depth of liquid in a tank.

Usage: Lower the tape into the tank until the bob touches the bottom. Pull it up to read the level at the wetted portion of the tape. It’s widely used for fuel, oil, ballast, and freshwater tanks.

2. Ullage Stick

Description: Similar to a sounding tape, an ullage stick measures the empty space above the liquid level (ullage) in a tank.

Usage: Lower the stick until it contacts the liquid surface. The reading shows the distance from the liquid surface to a reference point (usually the top of the tank).

For e.g. If the sounding tape is lowered till 500 cm and the tape measures oil in the tape as 100 cm. The total depth of the sounding pipe is 1600 cm. Hence the ullage is: 500cm- 100cm= 400cm, and sounding value can be calculated as

1600 – 500 +100 = 1200 cm

3. Sounding Rod

Description: A solid metal rod, often graduated, used primarily for measuring in smaller tanks where tapes might not be suitable.

Usage: The rod is inserted into the tank, and the wet mark left on the rod indicates the level.

4. Water-Finding Paste and Fuel-Finding Paste

Description: Special pastes applied to sounding tapes or rods that change color upon contact with water or oil, helping to differentiate between different layers of fluids.

Usage: The paste is smeared on the bottom of a tape or rod before measurement. It changes color upon contact with the specific fluid, indicating the water or fuel level in mixed-content tanks.

5. Dipstick

Description: Special pastes applied to sounding tapes or rods that change color upon contact with water or oil, helping to differentiate between different layers of fluids.

Usage: The paste is smeared on the bottom of a tape or rod before measurement. It changes color upon contact with the specific fluid, indicating the water or fuel level in mixed-content tanks.

6. Ruler or Graduated Scale

Description: Used for open tanks where levels can be measured directly.

Usage: Place the ruler or scale into the tank to measure the liquid level.

7. Calibration Charts

Description: Not a tool per se, but essential for converting measurements from sounding tapes, rods, or other manual methods into volume or capacity figures based on tank geometry.

Usage: After taking a level measurement, refer to the calibration chart specific to the tank to find the corresponding volume.

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