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

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 1,275 kg (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 with many thousands reliably in service around the world.

ORTs and DORTs are controlled using frequency band specific Lightweight Command Units (LCUs) which comprises of a dunking transducer connected either to an iRelease 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.

The Programmable Deep Oceanographic Release Transponder (P-DORT) combines the features of a heavy duty acoustic release transponder with hardware to allow automatic release at depth.

The P-DORT has two modes of basic operation. Firstly, like a standard DORT, it responds to securely coded acoustic commands from the surface in the LF (8–14 kHz) frequency band. Secondly, it can be pre-programmed prior to deployment to automatically release when it reaches a certain depth.