‘Vital signs’ of key systems
Bilge water levels (including any separate engine bilge), duty cycle of automatic bilge pump(s), battery level
All three signs are required to understand issue and severity, e.g. bilge water level may be ‘medium’ and stable, however if bilge pump is running repeatedly and battery voltage is low, the captain knows they have limited time to take contingency action – e.g. seeking shelter to enable crew transfer to tender in safety.
Tender instability
Surging and yawing of the tender in building sea and swell height
The tow arrangement is likely to fail first under shock load, generated when tender surges on a wave and overruns tow, so towline goes slack then takes up again with a shock often exposing the weakest part of the tow system.
Tender motion
Pitching and rolling in difficult sea conditions, bow down trim, angle of list
Increased key motions indicates tender no longer in the stable configuration when tow started and must be rectified.