A Diving Support Vessel is a vessel used as a floating base for professional diving projects. The key requirements are the ability to accurately and reliably maintain position throughout a diving operation, often in close proximity to drilling or production platforms, to allow positioning to degrade slowly enough in deteriorating conditions to allow divers to be recovered without undue risk, and to carry the necessary support equipment for the diving mode being used.
Modern offshore diving support vessels are typically dynamically positioned (DP) and double as ROV support vessels, and are also capable of supporting seismic and cable laying operations. DP enables a wider range of operations, but the platform presents some inherent hazards, particularly thrusters, making bell launch and recovery common. They may use a moon pool to protect the position where the bell or ROV enters and exits the water, and the launch and recovery system may also use a bell cursor to limit relative motion through the splash zone and heave compensation to minimise bell depth change during the dive. Accommodation should be provided for crews supporting the functions for which the vessel is contracted.
DSVs for nearshore operations are generally much smaller and may operate while moored for shallow water operations. Boat operations are considered unacceptably hazardous for surface diving unless a step or bell is used to hold the divers' umbilicals away from the vessel's thrusters
