The Sonardyne Lodestar has become the first marine AHRS (Attitude Heading and Reference System) using “strapdown” inertial sensors to receive the Wheelmark approval. Such sensors are rigidly strapped down, or attached, to the body of the unit resulting in size and weight reductions, lower cost, and greater reliability. The Wheelmark is the European standard that confirms it has been designed and approved to meet performance standards of Resolution A424(XI) and A694(17) of the IMO (International Maritime Organisation).
The certification followed an intensive testing programme and now enables ship operators to use the gyro compass output of the Lodestar for a range of applications. These can include primary navigation and as a feed for helm, autopilot, radar and ECDIS (Electronic Chart Display and Information System.) This is expected to prove particularly attractive to the operators of ships and offshore vessels that need high standards of heading accuracy for a variety of applications in the subsea construction and survey sectors.
In addition to providing highly accurate vessel heading, Lodestar is also a single, cost efficient, source for heave, roll and pitch data. This can be applied to dynamic positioning systems (DP), helideck monitoring and compensation for mulitbeam sonar and acoustic positioning systems. The Wheelmark certification now means that vessel operators can use a single Lodestar for a wide range of tasks and remain confident that it meets the necessary IMO standards.
Lodestar is a solid state AHRS incorporating six sensing elements, three ring laser gyros (RLG) and three linear accelerometers. It is an extension of the Sonardyne product range and was developed for seamless integration with the company’s widely used LBL (Long BaseLine) and USBL (Ultra-Short BaseLine) acoustic positioning systems. Lodestar is available in surface or subsea configurations depth rated up to 5,000 metres.
The gyrocompass algorithm calculation developed by Sonardyne for Lodestar produces output in real time for heading, roll and pitch. Because of the precision of the sensing elements used in the unit, the instrument produces a highly accurate solution for each rotation in the x, y and z-axis.
Lodestar also provides a robust heave measurement solution by applying a heave algorithm to the vertical motion of the unit. Lodestar is consequently suitable for any application that requires the accurate measurement of heading, heave, roll and pitch in a dynamic marine environment. By combining a motion sensor and gyrocompass in the same unit, significant advantages can be gained in relation to system calibration as the heading and motion frame share a common internal alignment axis. Lodestar is upgradeable to full Inertial Navigation System (INS) providing position, velocity, orientation and angular velocity at high update rates.