The Release Mechanism
A central element of any acoustic release is its release mechanism. The function of the release mechanism is to open a gate to release an anchor line and attached anchor weight, which allows the now buoyant assembly to travel to the surface. There are also variations of this use, such as exemplified by Kintama Research where a light-load release sets free a flotation sphere, which travels to the surface trailing a strong tether that remains attached to the instrument. The sphere is recovered and the heavy instrument is then hauled aboard using a winch.
The general function of a release mechanism is shown in figure 2, using the example of a fusible link release, a patented mechanism. Prior to release, the lever (A) is held in the closed position by a fusible wire (B). To trigger the release, a jolt of electricity of approx. 14 kW is passed through the fusible wire, causing it to melt or evaporate in a matter of a few milliseconds. The lever is now free to open (by the force of the instrument flotation), releasing the anchor or other release line (C).
The design goal for release mechanisms is maximum reliability while offering an appropriate load rating. Release mechanisms can fail due to bio-fouling or corrosion that can impair the motion of its components, failure modes that designers try to counter by minimizing the count of moving parts subject to seizing or applying high torque to overcome resistance. But failures also occur due to factors of use and environment such as rigging and ocean currents or surge that can result in an entanglement of the device.
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| Mechanism type | Method and characteristics | Sample devices | |
| High-torque motor | A strong motor opens a gate. Motor releases can handle heavy loads up to thousands of pounds. However, containing several moving parts, they are also relatively complex and bulky. Motorized mechanisms are employed by numerous manufacturers. | Benthos 865, IXSEA, Sonardyne COMPATT 5, ORE CART, ORE 8242 | |
| Fusible link | A wire is rapidly melted or evaporated using a strong jolt of electricity. The mechanism is fast acting, very compact, and, with a single moving part, simple. However, a load limit of tens to 100 pounds generally restricts this release to smaller instruments unless mechanical advantage is used. | Desert Star Systems ARC-1 | |
| Electrolytic erosion | A stainless steel wire loop holding the anchor line is electrolytically eroded by a DC current. This mechanism is very simple with no moving parts. However, the erosion process takes several minutes and depends on water salinity. Like the fusible link release, this release is generally used with lighter loads. | Sub Sea Sonics AR-60 | |
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