Competence assurance for rotational and offshore crews

Rotation makes competence assurance awkward. The assessor and the person being assessed are on opposite rotations, the evidence sits on an installation with limited bandwidth, and a certificate expires while someone is on leave. What we see working is assessment planned into the rotation like any other scheduled task, assessors on each crew rather than one central assessor, and expiry dates managed against the rotation calendar rather than the calendar year. How do you handle it, and what happens when someone arrives offshore with a lapsed certificate?