Under Keel Clearance, Squat & Tidal Margin Tool

Static UKC • Dynamic UKC • Squat • Tide • Heel • Wave Response • CATZOC • Speed Envelope • S-129 UKCM

Under Keel Clearance, Squat & Tidal Margin Tool

Screen critical shallow-water points and route legs from charted depth through tide, draft, squat, dynamic motion and survey uncertainty. The tool separates static from dynamic UKC, compares the result with the entered company or port minimum, and estimates the speed, tide or draft change needed to recover margin.

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Need much more depth? Click Advanced above.Advanced adds forward/aft drafts, density correction, route legs, CATZOC depth uncertainty, heel/wave allowances, custom squat coefficients, tide × speed envelope, draft/cargo recovery and passage-readiness checks.

Fast10 primary inputs

Core answerDynamic UKC + margin

VisualWater column + speed curve

Single Critical Point

Use the controlling charted depth, actual passage draft and the port/pilot/company minimum UKC. Simple squat is either an approved manual value or a clearly labeled Barrass empirical screen.

Vessel type

Governing static draftm.

Charted / controlling depthm relative to chart datum / controlling reference.

Predicted tide / water levelm above chart datum. Negative allowed.

Speed through waterknots, not SOG.

Waterway type

Squat basis

Approved / manual squatm. Used only when manual squat is selected.

Combined non-squat allowancem for heel/wave/survey/water-level/other allowance.

Minimum required dynamic UKCm from port, pilot, company or approved procedure.

Vessel & Passage Basis

Vessel type

LOA / reference lengthm.

Beamm.

Block coefficient CbUsed only by empirical squat screening.

Forward draft

Aft draft

Governing static draft basis

Fresh Water Allowance (FWA)mm at summer displacement.

Water densityt/m³.

Density correction

Squat & Depth-Uncertainty Methods

Squat method

Custom squat multiplier kUsed only for custom method.

Depth uncertainty method

Additional datum / echo-sounder allowancem added to each route-leg uncertainty allowance.

Additional Master / pilot planning reservem above each leg's formal minimum UKC.

Reduced-speed recovery casekn for comparison.

Advanced Route-Leg Register

Enter each critical channel, bar, berth approach or turning basin separately. The route result is controlled by the lowest dynamic UKC margin. Leg/location text is for on-screen use only and is not sent in Tool Data.

Leg / location	Depth m	Tide m	Surge m	WL uncert m	Speed STW	Current	Waterway	Manual squat m	Heel °	Wave m	Other m	CATZOC	Manual survey m	Min UKC m

Commercial / Loading Context

Optional planning values. These do not change the navigation gate.

TPC at passage displacementt/cm.

Vessel / berth delay valueselected currency/day.

Expected tide wait if window missedhours.

Extra cargo net contributionselected currency/tonne.

Currency

Use draft reduction as recovery option

Passage Readiness

Latest chart / ENC and notices appliedControlling depth and obstructions are current. Latest tide / water-level source verifiedPredicted and observed water levels are appropriate. Port / pilot UKC requirement confirmedNo generic threshold replaces local requirements. Vessel draft verified for passage conditionTrim, hog/sag, density and ballast changes reviewed. Squat basis accepted for this waterwayPilot/port/vessel data takes priority over empirical screening. Weather / wave response reviewedHeave, pitch, roll and surge allowances included as required. Passing / bank interaction reviewedMeeting, overtaking and close-bank effects considered. Contingency / abort point identifiedPlan includes action if tide, speed or UKC deviates.

Navigation limitation: this tool is a passage-planning screen, not a navigational authorization. It does not replace the Master’s judgement, pilot advice, port UKC policy, official ENC/chart and notices, hydrographic/tidal services, vessel-specific squat data, dynamic UKC service, loading computer, stability information or company SMS.

Reference basis: IMO Resolution A.893(21), Guidelines for Voyage Planning, calls for safe speed in relation to available depth, allowance for increased draught from squat and heel when turning, and minimum under-keel clearance in critical restricted-depth areas. IHO S-129 Under Keel Clearance Management Edition 2.0.0 is the first operational S-129 edition and has been in force since 1 January 2026. IHO S-67 / S-68 describe CATZOC and bathymetric-data accuracy. No universal IMO minimum UKC percentage is hardcoded; port, pilot, Administration and company requirements control.

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Under Keel Clearance, Squat & Tidal Margin Tool