Ship-to-ship transfer operations take place at open sea or at OPL (outer port limit).
Due diligence should take place in the following phases of the Ship-to-Ship operation: The level of due diligence exercised by technical operators and Masters is mainly governed by SOLAS chapter IX (the ISM Code) which mandates the assessment of "objective evidence" towards actions that will ensure safety.
Although the term "due diligence" is vague, its application will be challenged either during an incident investigation, or relevant litigation.
Technical operators should have the means to prove that they are in compliance with both commercial guidelines and statutory requirements.
One should account prevailing weather conditions and most important the interaction forces exerted during approaching.
At that moment the vessel approaches on the quarter of the mother ship and gets on a parallel heading at slow speed.
That's why we will not consider a static reference system but one in translation because a ship needs some speed to maintain her heading.
According to International Maritime Organization regulations vessels transferring OIL CARGO must have an approved STS operational manual that describes the procedure.