Acoustic Releases

ORTs and DORTs are controlled using a frequency band specific Lightweight Command Unit (LCU) which consists of an over-the-side dunking transducer connected either to a splash-proof handheld terminal or, via supplied software, to any PC.

The Type 7663 unit is a Medium Frequency LCU for commanding ORTs whilst the Type 7667 LCU is a Low Frequency unit suitable for use with DORTs

For security of operation, a special coding system provides protection against accidental release by noise or acoustic transmissions from other equipment. Each ORT or DORT has its own unique ‘address’ enabling a number of units to be deployed in the same area without risk of interference.

• Commands and controls ORT and DORT transponders
• Choice of MF or LF operating band depending on acoustic release type
• Controlled using splash-proof Psion handheld terminal or PC
• Supplied with dunking transducer and 40 meter cable drum
• Allows users to range to Compatt transponders and send basic commands

Oceanographic Release Transponders (ORTs) and Deep Oceanographic Release Transponders (DORTs) are tough, reliable acoustic releases designed for deployment in either 2,000 metres or 6,000 metres of water.

• Standard Safe Working Load of 1,275kg (Options for heavier loads)
• Up to 50 tonnes SWL with optional heavy duty release frame
• 2,000 Metre or 6,000 Metre depth rated options
• Highly reliable release mechanism
• Up to 2 years deployment
• Excellent corrosion resistance
• Compact and rugged design

The units are commonly used to moor oceanographic instrument strings on the seabed for periods of up to 36 months. However, their compact size allows them to be easily incorporated into subsea instrument frames or installed on towfish and AUVs to enable ballast to be dropped in an emergency.

Standard features include a Safe Working Load of 1,275kg (at 4:1) and a spring-assisted release mechanism. This type of release mechanism was originally developed by Sonardyne for navigation transponders supplied to the offshore industry of which there are now many thousands reliably in service around the world.

ORTs and DORTs are controlled using frequency band specific Lightweight Command Units (LCU) which comprises of a dunking transducer connected either to a spray-proof Psion or, via supplied software, to any PC. For security of operation, a special coding system provides protection against accidental release by noise and acoustic transmissions from other vessels.

In order to increase the Safe Working Load (SWL) of a standard ORT, DORT, Heavy Load DORT, P-DORT and Heavy Load Compatt 5, Sonardyne offer a range of heavy duty release frames. The frames act as a load amplifier so that only a fraction of the mooring load passes through the acoustic release. Applications include: offshore construction, marine salvage, defence and oceanographic research.

• Safe Working Loads up to 50 Tonnes
• Heavier load frames available on request
• Designed around proven ORT and DORT releases
• Compact size; just over 1 metre long
• Galvanically isolated from acoustic release to maximise corrosion resistance
• Uses industry standard master links

Manufactured from high strength steel which is galvanised and painted, the release frames offer excellent corrosion resistance and are suitable for long term deployment. This can be up to three years if the acoustic release is fitted with a lithium battery pack.

Depending on the type of acoustic release being used, the SWL of the unit can be increased up to 50 tonnes. All the frames can be easily assembled in the field and in most cases, fitted without any modification to the transponder itself. Custom frames for special applications or higher load ratings are available on special request.

LRTs, LATs, Coastal Transponders and TZ/OBC Transponders are commanded using a Type 7967-000-01 transponder deck unit. The system comprises of a deck unit and dunking transducer supplied with 10 metres of cable.

The deck unit is used initially to program the acoustic identity of the transponder, test the transponder and, in the case of the LRT (Lightweight Release Transponder), load the release ‘bit’ prior to deployment. Once deployed, it can be used to measure ranges to the transponder and prior to sending a secure release command, relocate the transponder. The deck unit can also be controlled via RS232 enabling raw range data to be logged to a PC.

• Supplied in rugged, portable case
• Provides command and control of LRTs, LATs and TZ/OBC transponders
• Enables transponders to be tested and programmed with thousands of unique identities prior to deployment
• Highly secure coding sequence prior to commanding LRTs to ‘release’
• Powered by alkaline battery packs; supplied with 2 spare packs
• Can be connected to a PC to enable raw ranges to be collected
• Easy to operate

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

• Safe Working Load of 125kg
• Depth rated to 500 metres
• Over 4 years deployment with long-life Lithium battery pack
• Thousands of secure identities; field programmable with deck unit
• Reliable, ‘screw-off’ release
• Rugged, compact design
• Compatible with Scout USBL, ROV-Homer, Homer-
• Pro and Prospector positioning / relocation systems
• Optional rope canister with 75 metres of 1200kg breaking-strain rope
• Optional tilt indication if ±30° off vertical

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.