OM-7986
Page 4 of 23
Issue A - Rev 8
1.
INTRODUCTION
The Type 7986 Lightweight Release Transponder (LRT) has been designed for use in
continental shelf waters to water depths of 500 meters. The unique design enables small
strings of instruments or seabed devices to be deployed without a surface marker and
automatically recovered upon acoustic command from the surface.
The transponder has been designed to be low-cost, enabling acoustic releases to be
economically and operationally viable in applications where they have traditionally not been
used. At the same time the unit is extremely reliable and rugged, the design being based on
Sonardyne’s successful and well proven Ocean Bottom Seismic positioning system.
The transponder is designed to be small, lightweight and long-life, with field replaceable
alkaline or lithium battery packs giving a listening life from 18 to 51 months.
The unique positive-action release mechanism ensures high reliability even in high bio-
fouling areas. The plastic material used for the release ‘nut’ is impregnated with lubricant to
limit bio-fouling.
The unit is designed to a Safe Working Load (S.W.L) of up to 125kg.
On the deck, using the Type 7967 Surface Unit, the transponder can be programmed in the
field to one of over 3600 unique acoustic identities.
Using various surface systems the transponders can be interrogated to determine the slant
range from the vessel to the transponder. This enables the operator to confirm the
transponder is operational and within range. If the unit has been dragged from its original
location it also enables the transponder to be relocated.
To release the transponder the operator must send 3 unique and secure messages to the
transponder. Upon receipt the transponder replies and activates the motor to turn the
release shaft. This drives out the release ‘nut’ breaking out any bio-foul material and enables
the unit to return to the surface under its own buoyancy.
The transponder is compatible with Sonardyne’s Homer-Pro system, a hand-held relocation
system for use by divers. The unit gives range and direction to swim to guide a diver towards
the transponder. ROV-Homer, the remote vehicle mounted version, can also be used in a
tow-fish for relocation sweeps.
The transponder is also compatible with Sonardyne’s low-cost Long Base Line navigation
system (ROV-Trak) which enables divers or ROVs to be accurately positioned and navigated.
As an optional extra the LRT can be retro-fitted with a variety of rope canisters. On release,
high strength recovery line is deployed from a canister on the side of the LRT, currently there
are options up to a maximum of 160 m. It should be noted that the recovery line may have a
lower safe working load than the LRT.
The 7986-000-06 version of the LRT is fitted with a
Tilt indication
feature, see label. The
ranging behaviour changes if the unit is tipped more than 30 degrees from vertical, as it will
only reply to alternate ranging interrogations if it is tilted.
