Anchoring secures a vessel in a fixed general position using its anchor and chain, relying on the anchor’s grip on the seabed to resist the forces of wind, current, and tide.
Choosing an Anchorage
Key factors in selecting where to anchor:
- Adequate depth — enough water depth for the vessel’s draft with safety margin, accounting for tidal range
- Suitable holding ground — seabed composition (sand and mud generally hold well; rock and hard seabed poorly)
- Swinging room — sufficient space for the vessel to swing with wind/current changes without risk of grounding or collision with other anchored vessels
- Shelter from weather, where practical, given forecast conditions
Scope of Chain
The amount of anchor chain paid out (“scope”) relative to water depth significantly affects holding power — more scope generally provides better holding, and standard practice calculates minimum scope based on depth and expected conditions.
Anchor Watch
Once anchored, a continuous anchor watch is maintained to monitor the vessel’s position, since dragging anchor (the anchor failing to hold and the vessel drifting) is a real risk, especially in deteriorating weather. Watchkeepers check position fixes at regular intervals against the vessel’s expected swing circle.
Dragging Anchor
If a vessel’s position moves beyond expected limits, this indicates the anchor is dragging — requiring immediate action, potentially including heaving anchor and re-anchoring, or getting underway if conditions are deteriorating seriously.
Exam Relevance
Anchoring procedures, scope of chain calculations, and anchor watch responsibilities are core Navigation and Ship Knowledge topics in deck officer competency exams.