Acoustic Release AR-50-AA

(Lower Cost System)

This acoustic release is used to release one or more lines underwater upon the receipt of an acoustic signal from the surface. It is commonly used for the release of a float and coil of line that is attached to an object of interest. There are many additional ways of deploying this release unit.

(Note: This release works in ocean water and typical bay water. It will not work in fresh water since the electrolytic erosion will not occur at a fast enough rate).

Click on the photos below for detailed descriptions.

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  1. Release upon receipt of an acoustic signal by the process of electrolytic erosion of a hoop of metal wire.
  2. Slant range 1,000 to 3,000 feet and up depending on water conditions. (Note: Sound travel is extremely variable in water depending on many factors).
  3. Operating depth is 0 to 600 feet (180 meters).
  4. Topside interrogator is set to the four digit identification number of the unit underwater by pressing the increase or decrease key while viewing the unit identification number on an LCD display.
  5. The release unit has an external LED that flashes once every 10 seconds to indicate that the unit is on and listening and that the micro computer is fully operational. The system can be checked out in air to give assurance that all is operational just before deployment.
  6. The AR-50-AA acoustic release unit uses nine lithium ‘AA’ cells and has a battery life exceeding one year plus many releases.  See menu item ‘Release Links’.  The batteries pack is user accessible and replaceable by someone capable of soldering the two wires (red and black) to a replacement battery pack model BAT-50-AA-L91. As a lower cost operational option the user can make the battery packs.  If this option is considered it is suggested that one of the BAT-50-AA-L91 battery packs be disassembled and examined.

Click on the photos below to see the deployment of the AR-50-AA system

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Click here for a report on the AR-50-AA range and operation.
(Go to page 8 of the original document heading Methods: and heading Discussion:). (Look for ‘AR-50′ and ‘Sub Sea Sonics’ in the text). Note that this is a xxx.pdf file and may be slow to load.


AR-50-AA release deployed using a sacrificial weight.

Video supplied by NAUTA (see NAUTA-RCS.IT). (File size is 9.1 megabytes of type .wmv).


This release unit is deployed underwater and contains the receiver plus a micro computer and batteries and holds a release link with a screw-on retainer cap for link replacement. It turns on automatically when it is placed in the ocean by means of water contact to the link and the coil contacts. It has a unique 4 digit identification number that has been assigned to it by the factory. This identification number is entered into the topside acoustic release interrogator (ARI-50) when a command is sent. When the release command is received the unit applies its full battery voltage to the link (pos) and the ‘coil’ (neg) for 15 minutes. This causes the small hoop of metal to erode away effecting the release. This release unit has a single green LED that flashes once per 10 seconds when the unit is on and listening. There is a checkout command that can be sent to cause the unit to switch on the erosion voltage for only 10 seconds which is useful for checkout.  See picture above for dimensions.

An extra feature of the AR-50-AA release unit is that it can be commanded to emit low power (10 milliwatt) acoustic pings. Receiving these low power pings requires a special acoustic receiver and antenna not supplied with this system. Most users will not have the necessary receiving system but for those who do this signal can be used for verifying that the unit is operational or for locating the unit by sending it a command to emit pings for one minute. Another command ‘release-with-ping’ can be sent to cause the unit to ping for 15 minutes while the release erosion is in process. (Note that the 10 miliwatt power of this reply pinging is so low that it requires a good antenna, a good receiver, and quiet water conditions to pick it up at 1000 foot range.)

EROSION LINKS LK-xx (see menu item ‘Release Links’)

The erosion links are made from a hoop  of metal wire encapsulated in a PVC plastic holder. The erosion link operates by the fast electrolytic erosion of the exposed metal part of its hoop thereby freeing any line passed through it. This occurs when a positive voltage is connected to it by the internal electronics. It is partially coated with a durable paint to restrict the intended erosion to two points at the base of the hoop to speed the release and reduce battery consumption. The erosion link is replaced after each release. An O-ring is used to keep salt water out of the link connection cavity.  A fresh battery pack (BAT-50-AA-L91) will last more than one year.  See menu item ‘Release Links”.


The interrogator is used to send the acoustic signal to the release unit. With it comes a transmitting transducer (TD-50) which is placed over the side of the boat and into the water. First the unit identification of the release unit to be released is set using the increase and decrease keys and viewed on an LCD display.  Second the specific action desired is selected (e.g. release w/ ping). Third the command is transmitted. The signal takes about 15 seconds to send. When a release command is received by the underwater release unit (AR-50-AA), the release unit starts the erosion process.