n Sub-second control of a rudder actuator, with a feedback loop in order to control heading in response to Heading and Rate of Turn (ROT) set points;
n Following a sequence of waypoints by issuing Heading and ROT set points; n Generating or selecting waypoints, and selecting which route to follow; n Enabling waypoint-following, or superseding the mission controller with heading and speed set points calculated by a collision avoidance algorithm.
7.9.2 Note that the MASS’s ability to transmit situational awareness data to an off-board controller has been covered in the previous Section. This, and the ability to receive appropriate and timely commands from the controller, should be borne in mind in cases where some of these functions are performed remotely.
7.9.3 The control functions, (on-board, remote, or distributed) shall be capable of exerting timely and accurate control in such a manner as to maintain safety of (1) the platform; (2) surrounding persons, structures, vessels; and (3) the environment.
7.10 Emergency Stop
7.10.1 The MASS shall have a defined condition of Emergency Stop, which must be fail safe under conditions where normal control of the MASS is lost. Under Emergency Stop, propulsion is reduced to a safe level in a timely manner. In this context:
n “a safe level” means a level at which it is not likely to cause damage either directly or indirectly; Note that some MASS (e.g. wave propelled) may not have any means of cutting propulsion power to zero; but in a harbour or sheltered waters the wave propulsive power may reasonably be expected to be a safely low level;
n “in a timely manner” means within a time that is short enough to ensure that the risk from uncontrolled propulsive power can be contained before it is likely to cause damage. In open ocean conditions this may be relaxed, whereas in a docking situation the propulsion may need to be cut more quickly, within seconds or less.
7.10.2 The MASS shall have the ability to be placed in an Emergency Stop condition by a human or automatic controller or supervisor with access to sufficient Situational Awareness data to be able to determine when an Emergency Stop command is necessary.
7.10.3 In the case of an automatic operator, the design of that controller or supervisor shall be fail safe, in that it shall recognise all known unsafe operating conditions with no false negatives, and shall react to unknown or indeterminate safety conditions by invoking Emergency Stop in a timely manner.
7.10.4 On sensing a failure (or disabling, whether deliberate or not) of all data-links which may carry an emergency stop command, the MASS shall enter a ‘render-safe’ procedure. This should culminate in Emergency Stop. The first action should be that, if situational awareness has been, and continues to be, fully operational, the MASS should immediately shape a safe course and adopt a ‘safe speed’ (making appropriate sound and visual signals when feasible) commensurate with weather conditions, COLREGS and safe navigation at the time of loss of data-link. This should minimise hazards to the MASS and other vessels, whilst the MASS and the control station resolve the situation. If the data-link is not re-established after an appropriate grace time, and/or the MASS’s own situa- tional awareness deems it safe/necessary, the MASS should enter Emergency Stop. Consideration may be made of including ‘dropping anchor’ as part of the render-safe procedure, commensurate with accepted safe navigation practices.
7.10.5 In the event that the MASS experiences loss or compromise of Situational Awareness as well as loss of data- link, then Emergency Stop should be immediately initiated (making appropriate sound and visual signals when appropriate).
Maritime Autonomous Surface Ships up to and including 24 metres in length 35
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