Positive buoyancy comes from objects that have an upward directed force when submerged, that is, objects that have a density that is lower than the water around it. Negative buoyancy represents a downward force. To determine the buoyancy of an object, knowledge about the mass and the volume of the object is essential. Remember that the actual buoyancy is the mass of the seawater the object displaces minus the mass of the object (Archimedes' Law). It is of primary interest to keep a mooring as vertical as possible; therefore, sufficient buoyancy is essential, at the same time as the handling of the deployment is not affected (e.g. not too heavy).
The apparent immersed weight of an object in water can be calculated using (1):
| \begin{equation} \text{Apparent immersed weight} = \text{weight of object} - \text{weight of displaced fluid} \end{equation} |
(1) |
Here, the weight of the displaced fluid is constant and depends on the volume of the object submerged. This remains consistent even when the object's contents (such as batteries) change. In the context of determining buoyancy for instrument deployment, the primary task involves straightforward addition and subtraction to account for changes in the object's weight when submerged. Understanding these principles is fundamental for optimizing the design and performance of underwater equipment.
For detailed buoyancy data, visit our website. Under "Products," locate your specific instrument, and under "Technical Documents" or "Technical Drawings," you'll find a general assembly drawing containing all the necessary information for buoyancy calculations. Due to the variety of battery combinations available, we only specify the weight of the instrument itself. To determine the total instrument weight with additional batteries, simply add the weight of the chosen battery option. For specific battery weight information, refer to our website under "Products" and "Spare Parts."
If weight details are not provided on the drawing, please reach out to Nortek Support for assistance.
Example calculations
Signature 500 with Standard Housing and 180Wh Battery:
- Weight in Air:
- Weight of Signature 500 (standard housing, no battery): 6.4 kg
- Weight of 180Wh battery: 1.8 kg
- Total weight in air: 6.4 kg + 1.8 kg = 8.2 kg
- Weight in Water:
- Weight of Signature 500 (standard housing, no battery): -0.3 kg
- Weight of 180Wh battery: 1.8 kg
- Total weight in water: -0.3 kg + 1.8 kg = 1.5 kg
Signature 500 with Long housing and 540Wh Battery:
- Weight in Air:
- Weight of Signature 500 (long housing, no battery): 8.6 kg
- Weight of 540Wh battery: 5.1 kg
- Total weight in air: 8.6 kg + 5.1 kg = 13.7 kg
- Weight in Water:
- Weight of Signature 500 (long housing, no battery): -2.5 kg
- Weight of 540Wh battery: 5.1 kg
- Total weight in water: -2.5 kg + 5.1 kg = 2.6 kg
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