Operation Type refers to the type of voyage being scheduled. These are system-defined and controls the business logic of how the voyage behaves.
The following default types are available:
OVOV: Owned Vessel, Own Voyage
OVTO: Owned Vessel, TC Out
RELT: Cargo Relet
TCOV: TC In Vessel, Own Voyage
TCTO: TC In Vessel, TC Out
VCOV: VC In Vessel, Own Voyage (must be enabled for you by Veson Nautical)