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.

Figures represent
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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

m below present water level to seabed.
m.
m for tide/surge increase.
m from anchor to fairlead.
kN/m.
kN before dynamic/load factor.
kN, user-entered for actual anchor/seabed/setting condition.
User/company screening target.
m added to anchor-to-fairlead radius.

Anchor Geometry & Chain

m.
m above water.
m.
m available for planning.
kN/m.
kN.
kN allowable/selected screen.
m.
m added outside furthest vessel point.
m beyond the zero-uplift catenary requirement.

Anchor Holding & Seabed

kN for the actual/assumed anchor and soil condition.
% applied to nominal horizontal capacity.
kN. Use 0 where uplift is not credited.
Dimensionless, only used if enabled.

Environmental Load Model

m².
kg/m³.
0° from ahead, 90° from starboard.
m².
kg/m³.
Used 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/sCurrent m/sOther horiz. kNLoad factorWater-level +m

Anchoring Readiness Checks

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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