A Lodestar is born
The first marine Attitude Heading and Reference System (AHRS) that used ‘ strap down’ inertial sensors has received IMO Wheelmark approval. The ‘ strapdown’ part of the system is particularly important because it means that sensors are directly attached to the body of the Sonardyne Lodestar unit, resulting in greater reliability while also giving size and weight reductions. It is also a cheaper alternative.
There are obvious advantages to combining a motion sensor and gyrocompass in the same unit. System calibration becomes simpler as the heading and motion frames share a common internal alignment axis.
Lodestar’s certification followed an intensive testing programme and this official recognition enables ship operators to use the gyro compass output of the unit for a range of applications, including primary navigation and as a feed for helm, autopilot, radar and ECDIS, while remaining confident that operations meet the necessary IMO standards.
It 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 source for heave, roll and pitch data. This can be applied to dynamic positioning systems, helideck monitoring and compensation for mulitbeam sonar and acoustic positioning systems.
The unit is solid state, incorporating six sensing elements, three ring laser gyros and three linear accelerometers. It has been 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 5,000m.
The gyrocompass algorithm calculation developed by Sonardyne for Lodestar produces output in real time for heading, roll and pitch data. Because of the precision of the sensing elements used in the unit, the instrument produces a precise solution for each rotation in the x, y and z axis. Directional accuracy comes to within 0.10 secant latitude rms, while roll and pitch readings are 0.01 accurate. Lodestar also provides a robust heave measurement solution by applying a heave algorithm to the vertical motion of the unit. Heave data is within 5% or 5cms (whichever is greater).
The unit is fairly robust, remaining operational at between -10C and +55C, at a depth of 5,000m. Once the system has had its five minute warm up, it provides virtually instantaneous updates at 500 per second.
