Ocean currents are continuous flows of water within the oceans, influenced by factors such as wind, temperature differences, salinity and the Earth’s rotation. They play an important role in regulating the global climate, distributing heat and influencing weather patterns in many parts of the world. In addition, ocean currents also have a significant impact on marine life and human activities. They play a role in the distribution of nutrients and organisms, which is critical to fisheries productivity and the health of marine ecosystems. On the other hand, changes in ocean current patterns due to climate change can lead to adverse impacts, such as an increase in the frequency and intensity of storms, and changes in habitat for marine species. Therefore, the collection and analysis of ocean current data is crucial in mitigating and adapting to environmental change. Ocean current velocity data are critical to understanding ocean dynamics and their interactions with the global climate. Current speeds can affect everything from the distribution of heat and nutrients in the ocean to the migration patterns of marine species. By monitoring current speeds, scientists can identify changes in the ocean system, which are often linked to climate phenomena such as El Niño and La Niña. In addition, ocean current velocity data also has significant practical implications for a variety of sectors, including fisheries, maritime transportation and marine resource management. In the fishing industry, an understanding of current velocity can help fishermen determine optimal fishing locations, as currents can affect the distribution of fish. On the other hand, in the context of navigation, knowing the current speed is essential for planning efficient and safe shipping routes. Thus, collecting and analyzing ocean current speed data not only supports scientific research, but also contributes to sustainability and efficiency in marine resource management. This material will discuss one of the marine portable instruments that is quite often used to measure current speed, namely the Current Meter.
Current meter Mechanical is a tool specifically designed to measure the speed and direction of water currents in aquatic environments, such as the sea in low or shallow water flow, rivers and lakes. This tool is the most widely used speed measuring device because it provides quite high accuracy. The measured flow velocity is the point flow velocity in a particular flow section. The principle used is the relationship between flow velocity and the rotating speed of the current meter propeller. The Basic Principle of Current meter is to work based on the principle of converting linear motion of water into angular motion. When the water current flows, the propeller or rotor on this tool rotates. The rotation speed of this rotor is then measured to determine the current speed. The current speed can be calculated by a formula involving the hydraulic pitch of the propeller and the number of propeller revolutions per second. The signal generated from the propeller rotation can be processed into accurate current speed data.
Components – components that exist in Current Meter Mechanics in general:
- Rotor or Impeller; This part rotates when water flows through it. The rotation speed of the rotor is proportional to the speed of the water current. The rotor is usually made of corrosion-resistant material and designed to minimize flow resistance
- Shaft; The shaft connects the rotor to the metering system. When the rotor rotates, the shaft also rotates and transmits this motion to the speed measuring part.
- Speed Indicator; This part converts the rotary motion of the shaft into a current speed value in readable units, such as meters per second (m/s) or knots. This can be a mechanical system (such as a dial) or an electronic system.
- Housing; The housing serves to protect the internal components from damage and provide a stable structure. It is usually made of materials that are water and corrosion resistant.
- Sensor or Transducer; Some modern mechanical current meters are equipped with sensors or transducers that can convert mechanical motion into electrical signals for further processing or data logging.
- Cable or Connecting System; If the device is equipped with an electronic system, a cable or connecting system is used to transfer data from the sensor to the reading device or data logger.
- Base or Support; Function: The base or support is used to stabilize the tool when used in water. This can be a foot or fastening system that allows the tool to remain in the desired position.
- Scale or Indicator; Function: Some mechanical current meters are equipped with a scale or indicator that shows the current speed directly, allowing users to read the measurement results without the need for additional tools.
How Mechanical Current Meter Work
Measurement of water current velocity with a Mechanical Current Meter can be done by several methods, including;
- Velocity Curved Method: This method requires measurements at many points in a vertical line from the water surface to the riverbed. In general, measurements are taken at every 1/10th of the depth. This measurement starts from point 0.1 or 10% of the depth up to 0.9 or 90% of the depth. This method is used to obtain accurate measurement results and is carried out at a representative location, where the water flow is quite stable and not affected by external disturbances
- Two-Point Method: A technique used to measure the velocity of water flow in a water body, such as a river or channel, using two measurement points at different depths. This method is often used because of its simplicity and its ability to provide a good estimate of flow velocity without requiring measurements across the entire cross section. technique used to measure the velocity of water flow in a body of water, such as a river or channel, using two measurement points at different depths. This method is often used because of its simplicity and its ability to provide a good estimate of flow velocity without requiring measurements across the entire cross section. In this method, two measurement points will be taken at different depths, usually at depths of 0.2 and 0.8 of the total water depth. The first point (0.2D) is at 20% of the total depth, and the second point (0.8D) is at 80% of the total depth, where D is the total depth of flow. Once the velocity at both points is measured, the average velocity of the flow can be calculated by taking the average of the two velocity values obtained. This average provides an estimate of the flow velocity in the cross section.
- Six-Tenths Method: The Six-Tenths Method is a technique used to measure flow velocity in a water body, such as a river or channel, by focusing on measuring the velocity at a single point within the flow cross-section. This method is based on the principle that water flow velocity varies with depth, and measurements at a specific point can provide a representative estimate of the average velocity across the cross section. In this method, velocity measurements are taken at a depth determined as 0.6 of the total flow depth. In other words, the measurement point will be at 60% of the total depth (D). If D is the total depth, then the measurement point will be at depth (0.6D)
Mechanical Current Meter Advantages and Disadvantages
- The relatively simple design makes mechanical current meters easy to understand and use, even by inexperienced users. .
- Mechanical current meters are generally more affordable compared to more sophisticated types of current measuring devices, such as acoustic or electromagnetic.
- They do not require an electrical power source to operate, so they can be used in remote locations without access to electricity.
- Mechanical current meters can be used in various types of water bodies, including rivers, lakes, and open channels.
- Sensitivity to Dirt and Sediment: Moving parts, such as the rotor, can be affected by dirt, sediment, or foreign objects in the water, which can reduce measurement accuracy.
- Limitations in High Current Conditions: In very fast or turbulent currents, mechanical current meters may not be able to provide accurate measurements as the rotor may get stuck or spin too fast.
- Depth Limitations; Most mechanical current meters can be used at depths of up to 10-20 meters.
- Limited Measurements at One Point; Mechanical current meters usually measure current velocity at one specific point, so to get a more complete current velocity profile, multiple measurements at various depths or locations are required.
Writer : Galuh Pramudya
