Notwithstanding that fact that tanker masters have to attend shiphandling courses and get the certificate, very often situation with awkward meneuvering at anchor leads to accidents or near-miss similar to those as this short movie represents.
Per Phillimore J in The Esk and Gitana (1869) L.R. 2 A. & E. 350:
The true criterion as to the application of the Regulation must be, whether the vessel be actually holden by, and under the control of, her anchor or not. The moment she ceases to be so, she is in the category of a vessel ‘Under-way’ and must carry the appointed coloured lights.