Anchoring and Working Anchors and Cables in All Circumstances
Holding Ground vs. Holding Power
These are not interchangeable. Holding ground is a seabed characteristic — how well the substrate grips an anchor. Good holding: firm sand, clay, soft mud. Poor holding: rock, weed, shingle, coral. Holding power is an anchor's mechanical ability to resist the catenary load given its type, size, and the scope deployed. A stockless anchor in firm sand with 7:1 scope has good holding power; the same anchor on rock may have almost none regardless of scope. The examiner wants you to distinguish cause from effect.
Anchor Types and Their Applications
- Stockless (Hall/Pool): standard bow anchor on most commercial craft; stows flush in hawsepipe; adequate general holding, poor on rock/weed.
- CQR/Delta (plough): suits small yachts; superior in sand, weed, soft mud; resets well when wind shifts.
- Danforth/Fortress: high holding-to-weight ratio; excellent in sand and firm mud; poor on rock; favoured as kedge.
- Bruce/Claw: omnidirectional reset; moderate holding; common on leisure craft.
- Kedge: any secondary anchor, often lightweight, used to haul off, prevent swinging, or lay a second anchor in a riding condition.
At command level you must justify anchor selection relative to forecast conditions, holding ground, and vessel characteristics — not just name types.
Scope, Catenary, and Cable Type
Scope is the ratio of cable length deployed to depth of water (add freeboard to hawsepipe height for true depth). A minimum of 3:1 is absolute minimum in calm conditions; 5:1 is working practice; 7:1 or more in heavy weather. The catenary — the sag in chain cable — absorbs surge loads and keeps the anchor pull near-horizontal. Wire cable has less weight and less catenary; it is faster to deploy but demands more scope and an anchor weight (kellet) to replicate catenary effect.
Kellet (sentinel): a weight clipped onto the cable and lowered partway to increase catenary, reduce swinging radius, and improve holding angle. Critical when swinging room is limited.
Letting Go vs. Walking Back
Letting go (free-fall): cable surges under gravity; used in a crash anchorage or emergencies. Risk: cable runs away before sufficient length can be controlled, or anchor fouls under the bow. Walking back: windlass controls the rate of lowering; preferred in normal operations — anchor is placed on the bottom before cable is surged, preventing pile-up of chain on top of the anchor.
Dragging Anchor — Recognition and Response
Signs: bearing change on fixed transits, radar overlay drift, GPS alarm, cable tending in a different direction, excessive snubbing. Response at command level: increase scope first; if dragging continues, let go the second anchor (open or tandem mould depending on conditions); start engines and use them to reduce load on cable; consider shifting berth.
Second Anchor Configurations
- Open mould (Bahamian moor): two anchors from the bow, each laid in opposite directions; limits swinging arc in a tideway.
- Tandem: second anchor on the same cable ahead of the first; increases holding power on a single lead without limiting swing.
- Fore-and-aft moor: one anchor ahead, one astern on separate cables; minimal swing, suited to confined anchorages with predictable wind/tidal axis.