Anchor Scope & Catenary Tool Holding Power, Chain Length, Swing Circle & Drag Risk

Anchor Scope • Static Chain Catenary • Touchdown • Holding Margin • Wind / Current Load • Fairlead Tension • Swing Circle • Zero-Uplift Chain • Drag Screen

Anchor Scope & Catenary Tool Holding Power, Chain Length, Swing Circle & Drag Risk

Screen an anchored vessel using more than a simple scope ratio. Simple mode calculates static all-chain catenary geometry under a specified horizontal load, identifies seabed contact versus full suspension, estimates anchor/fairlead loads, holding factor and swing radius. Advanced adds wind/current force buildup, anchor/soil derating, optional chain-on-seabed friction, chain and deck-holding-device utilization, reverse chain-length planning and multiple environmental scenarios.

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Need wind/current load buildup, MBL checks or multiple weather scenarios? Click Advanced above.Simple solves an inelastic static all-chain catenary and keeps holding capacity separate from chain geometry.

GeometryScope + touchdown + uplift

LoadsAnchor & fairlead tension

Watch circleLoaded + maximum swing

Anchoring Condition

Water depthm below present water level to seabed.

Hawse / fairlead height above waterm.

Additional water-level allowancem for tide/surge increase.

Chain paid outm from anchor to fairlead.

Submerged chain weightkN/m.

Mean horizontal environmental loadkN before dynamic/load factor.

Dynamic / load factor

Effective anchor holding capacitykN, user-entered for actual anchor/seabed/setting condition.

Required holding factorUser/company screening target.

Bow fairlead to furthest vessel pointm added to anchor-to-fairlead radius.

Anchor Geometry & Chain

Base water depthm.

Hawse / fairlead heightm above water.

Chain paid outm.

Maximum chain availablem available for planning.

Submerged chain weightkN/m.

Chain minimum breaking loadkN.

Deck holding device / stopper limitkN allowable/selected screen.

Bow fairlead to furthest vessel pointm.

Swing-circle safety clearancem added outside furthest vessel point.

Target chain lying on seabedm beyond the zero-uplift catenary requirement.

Anchor Holding & Seabed

Nominal horizontal anchor holding capacitykN for the actual/assumed anchor and soil condition.

Anchor / soil condition factor% applied to nominal horizontal capacity.

Vertical anchor capacitykN. Use 0 where uplift is not credited.

Required horizontal holding factor

Include chain-on-seabed friction

Chain / seabed friction coefficientDimensionless, only used if enabled.

Environmental Load Model

Wind projected aream².

Wind drag coefficient

Air densitykg/m³.

Wind direction FROM relative to bow0° from ahead, 90° from starboard.

Underwater projected aream².

Current drag coefficient

Water densitykg/m³.

Current set TOWARD relative to bow

Other-load direction TOWARD relative to bowUsed for wave/other horizontal load in scenarios.

Environmental Scenario Register

Each row independently builds wind/current/other horizontal load, applies its load factor, solves catenary geometry at the scenario water-level increase and checks anchor, chain, stopper and swing radius. Wind/current coefficients and directions come from the global inputs above.

Wind m/s	Current m/s	Other horiz. kN	Load factor	Water-level +m

Anchoring Readiness Checks

Anchor/chain certificates verifiedActual chain size/grade, MBL and anchor particulars are confirmed. Seabed / holding ground assessedHolding-capacity input reflects actual soil and anchor-setting quality. Depth and tidal range verifiedMaximum expected water level is included. Weather / current forecast reviewedScenario speeds and directions cover the required anchoring period. Swing circle clearCharted hazards, shoals, traffic, nearby ships and shore clearance are checked. Anchor watch / position alarms setDragging is monitored independently of this static calculation. Chain stopper / windlass arrangement verifiedOperational load path and allowable holding device are confirmed. Contingency plan preparedEngine readiness, second anchor, veering/heaving and departure criteria are defined.

Anchoring limitation: this is a static screening model. Real anchor performance depends strongly on seabed type, penetration/setting, vessel yawing, gusts, waves, snatch/dynamic loads, chain elasticity, seabed slope/friction, yaw angle, shallow-water/current interaction and operational handling. IACS anchoring equipment is intended for temporary anchoring in suitable conditions and is not designed to hold a ship off fully exposed coasts in rough weather or to stop a drifting/moving ship. Use ship/class/company guidance and the master/pilot’s judgment as controlling.

Method basis: static all-chain catenary equations use horizontal tension H, submerged chain weight per length w and a = H/w. With seabed touchdown and zero anchor uplift, suspended length s = √(h² + 2ah), horizontal suspended reach x = a·asinh(s/a), and fairlead tension combines H with suspended chain weight. If paid chain is shorter than the zero-uplift suspended length but longer than the vertical separation, the tool solves the fully suspended catenary and reports vertical anchor load. IACS UR A1 uses a minimum chain scope of 6 as an anchoring-equipment design assumption and warns that poor holding ground significantly reduces anchor performance; this tool shows that context but does not treat scope 6 as a universal safe-operating rule.

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