Pop-up buoy
The pop-up buoy is recommended when use of a surface buoy is impractical. Most of the pop-up buoy’s life is spent submerged, secure from storms and surface traffic. It functions by attaching one end of a line to e.g. the bottom frame and the other end to the buoy. Upon receiving an acoustic command, the buoy rises to the surface and the line attached to the buoy can be used to pull up the equipment directly. The Spin buoy by Abyssus, the Fiobuoy by Fiomarine and the 875-PUB by Benthos are good alternatives. Make sure to obey the depth limitations specified by the manufacturer.
Acoustic release
An acoustic release system is deployed in-line on a mooring, close to the anchor. When activated from the surface unit, the release system disconnects from the anchor, and the mooring aided by its flotation elements, ascends to the surface for recovery. To ensure successful retrieval, it is essential that the mooring system has sufficient buoyancy to overcome the weight of the remaining submerged components. Buoyant elements should be strategically placed near the acoustic release and/or distributed along the mooring line. This ensures that once released, the mooring rises efficiently and reliably to the surface. If buoyancy is inadequate, the mooring may remain suspended in the water column or ascend too slowly, making it difficult or impossible to locate and retrieve.
It is recommended practice to utilize a pair of releases to provide redundancy. Ensure both units are independently addressable by the acoustic command system and conduct pre-deployment tests of each release on deck to confirm functionality.
Gimbal
When deploying instruments on uneven or sloped seafloors, maintaining proper orientation of the instrument head is essential for accurate data collection. In such cases, a gimbal mount is often used to ensure the transducer head remains upright regardless of minor variations in the seabed. The gimbal functions as a pivoting platform that uses gravity to self-level the instrument, keeping it aligned in the correct vertical orientation for reliable measurements. It must be properly balanced to function effectively. This means that a counterweight is required below the instrument, particularly for top-heavy sensors like the AWAC
It is equally important to ensure that there is enough vertical clearance beneath the gimbal. On uneven terrain or with seabed sediments that cause the frame to settle unevenly, the bottom of the gimbal assembly may come into contact with the seafloor. This contact can interfere with the gimbal's freedom of movement, potentially causing the instrument to tilt or become stuck in a non-upright position. In areas with strong bottom currents, a gimbal can become counterproductive. If the instrument is mounted in an open-bottom frame, water flow can enter from below and destabilize the gimbal mechanism. This can cause the instrument to oscillate, tilt, or behave erratically, negating the benefits of the self-leveling design and possibly leading to compromised data.
AquaFin / AquaClamp
Nortek's AquaFin optimizes the instrument’s ability to measure without flow disturbance while simplifying in-line deployment and be utilized when working with an Aquadopp. The AquaFin shackles in-line and swivels the instrument so that its beams always face into undisturbed flow. The need for an Aquafin depends on the mooring construction, e.g. whether the instrument is suspended below a surface buoy or deployed above an anchor using floatation elements. The instrument’s compass has no trouble compensating for the heading changes.
The AquaClamp is similar to the AquaFin in that it is used to mount an Aquadopp current meter or profiler on a mooring line. The AquaClamp mounts in-line in the mooring line, and it is used when clamping the instrument directly to the mooring line is not practical or desired. The AquaClamp provides a stable setup and will not rotate with the flow!
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