Lightweight Release Transponders


The Type 7986 Lightweight Release Transponder (LRT) has been developed from transponders capable of accurately positioning hundreds of seismic receiver nodes.

It has both receive and transmit functions, unlike similar low-cost release transponders, enabling accurate slant ranges to be measured, release actuation to be confirmed and its position to be accurately determined.

The LRT is depth rated to 500 metres making it the ideal choice for use in continental shelf waters. Field replaceable alkaline or lithium battery packs give a listening life of 18 months and 51 months respectively. A ‘screw-off’ release mechanism ensures a positive release action that overcomes any biological growth and all external parts are made of high strength plastics that provide excellent environmental corrosion resistance.

LRTs are controlled using the Type 7967 Deck Unit comprising a low-cost deck unit and remote transducer on 10 metres of cable. The deck unit is initially used to program the acoustic identity of the LRT, test the transponder and load the release nut prior to deployment. Once deployed, the deck unit can measure ranges to the transponder and prior to sending a secure release command, relocate the transponder. The deck unit can be controlled via RS232 enabling raw range data to be logged to a PC.

The transponder is compatible with Sonardyne’s ROV-Homer and Homer-Pro target relocation systems. Deployed at a point of interest and weeks or years later, the LRT can be interrogated to provide range and direction guidance to a ROV pilot or diver wishing to home back on to it.

Furthermore, the transponder’s exact seabed co-ordinates can be quickly and easily determined using Sonardyne’s Prospector system, calibrated from a dGPS positioned vessel.

A rope canister is also available for pop-up buoy applications, with 75, 120 or 160m lengths of high breaking-strain rope.

As an option, the LRT can give an indication that it is tilted beyond 30° from vertical using the acoustic link, allowing warning of incorrect string deployment before leaving the site.



Feature Type 7986
Depth Rating 500 metres
Operating Frequency HF (35-50kHz)
Transmit Source Level 185dB re 1µPa @1m
Number or Unique Addresses 3609 (Field Program)
Switch On Continuously Operating (No On/Off switch)
Battery Life Alkaline
Long Life Lithium
18 months
51 months
Safe Working Load (at4:1 ratio) 125 kg
Release Load 125 kg
Breaking Load 500 kg
Proof Load 250 kg (Note: A Proof Test Certificate can be provide upon request)
Mechanical Construction Plastic, Stainless Steel and Anodised Aluminum Alloy
Dimensions (LxDia) 63mm (2.4”) x 490mm (19.3”)
Weight in Air 1.7kg
Weight in Water 0.4kg
75, 120 or 160 Metre Rope Canister (Longer lengths available upon request)
Tilt Indication ±30° (Type 7986-000-06 Only)
Release Nut (Order Part No. 830-1641) Note: 5 nuts supplied with each new LRT
Deck Unit Type 7967-000-02 (Includes Transducer and 10 metres of cable)
Safe Working Load - The maximum recommended working load. This is set as a quarter (1/4) of the Breaking Load and allows for factors such as corrosion, fatigue, shock loads, harmonic loads, manufacturing defects and material defects.

Release Load - The maximum in-line load that the whole assembly can release whilst guaranteeing safe and reliable operation. Note that as the load is released in water, this is determined by the maximum upthrust from the buoyancy.

Breaking Load - The load that induces structural failure in one or more parts of the instrument causing the load to part from the release mechanism.

Proof Load - The load to which the actual unit has been tested in the factory. This load should be periodically applied to demonstrate that the unit is still in a safe condition. This is usually twice (x 2) the SWL. A Proof Load Certificate can be provided upon request