Problem
Oceanographic instruments are often moored at varying depths to collect data. Researchers then have to recover the instruments to obtain the data. Timed release mechanisms are often used to part the mooring cable. Mechanical devices have been used but they are susceptible to corrosion and fouling and are not always reliable. Explosive devices have also been used but they pose a handling hazard and are not allowed on some ships. AO was asked to develop a reliable, safe and inexpensive release mechanism.
Solution
We conducted research into the technique of parting a 200-lb nylon monofilament mooring line by melting it. This method has the advantage of no moving parts to foul or corrode and no explosives hazard. The load bearing mooring line passes through a close fitting tube filled with silicone grease to conduct heat to the line and exclude moisture and debris. An electrical heater raises the temperature of the tube above the melting point of the mooring line.
The release mechanism includes a processor to time the release and trigger the release mechanism. Our inductive interface is used to program the release time. A small battery powers the processor and a much larger battery provides power for the release mechanism. The entire assembly is encased in a urethane casting to keep the assembly dry and provide sufficient protection from pressure to allow the unit to be used in all but the greatest ocean depths. The nylon line is attached to shackles at both ends of the release. One shackle is attached to the release mechanism and the other is free to pull away after the nylon line melts.
Both the battery and heater elements are redundant. Test firing and replacement of the load bearing nylon monofilament can be performed to verify the unit is operating correctly.
Results
The 9522 Meltline Release has been used with a variety of oceanographic projects.
