The long awaited OSV STCW NVICs are now available on the OMSA website at: 

These four Navigation and Vessel Inspection Circulars (NVIC) outline the reduced formal training and assessments that will be accepted by an applicant for an STCW endorsement limited to service on an OSV.  They also announced that the existing 500 grt/3000 GT or 500 grt/6000 GT tonnage limitations will be removed from all existing OSV limited STCW credentials at the next mariner credential transaction!  For new OSV STCW endorsements issued under these NVICs, no tonnage limits will be placed on the Chief Engineer, Assistant Engineer (OICEW), and Mate (OICNW) endorsements. The Master/Chief Mate OSV has two tonnage limits;  less than 1600grt/3000 GT, or 1600grt/3000 GT or more, depending on the amount sea service above 1600grt/3000 GT.

Please see the OMSA website for more details.