QUESTION 4.2.2

Under-keel-clearance control

Oil, Chemical, LPG, LNGBridge

What is being checked

The inspector is checking whether the vessel maintains company-required static and dynamic UKC at every critical point using realistic depth, tide, squat, heel and survey-accuracy inputs, and whether plans, records and interviews demonstrate that the procedure is applied during real voyages rather than completed only as paperwork.

Ready onboard

0/6 complete

PROCEDUREThe UKC policy defines minimum margins, calculation points, CATZOC or survey allowance, squat method, tide source, wave response and escalation below plan.EVIDENCERecalculate the latest critical point from charted depth, height of tide, draft, squat, heel or list, density, wave allowance, CATZOC and company margin.RESPONSIBILITYThe Master and responsible officers can identify who prepares, verifies, approves and monitors each stage.DRAFTMaximum actual or expected draft includes density, hog or sag and operational change.SQUATThe method reflects vessel speed, blockage, channel geometry and the relevant critical location.ECDIS LINKSafety contour, safety depth and no-go areas follow the approved UKC result and available ENC contours.

Practice questions

Answer aloud, then open the preparation point.

1What is the operational purpose of under-keel-clearance control?

The vessel maintains company-required static and dynamic ukc at every critical point using realistic depth, tide, squat, heel and survey-accuracy inputs.

2Show how the procedure was applied on the last voyage.

Recalculate the latest critical point from charted depth, height of tide, draft, squat, heel or list, density, wave allowance, CATZOC and company margin.

3Which decision requires the Master's judgement?

The Master decides whether source uncertainty and actual conditions justify an allowance greater than the policy minimum or require speed, timing, route or loading change.

4What happens if the planned control becomes invalid?

Reduce speed or alter timing and route as safe, obtain updated local data, recalculate, notify the company or authority under policy and do not proceed below an authorised safe margin.

5How are changes communicated and recorded?

Brief the affected bridge and machinery personnel, amend the controlled plan or record, obtain required approval and retain the reason and revised limits.

Where an observation may arise

PAPER COMPLIANCE

Records exist but the bridge team cannot relate them to the actual voyage or operation.

CHANGE UNCONTROLLED

A material change is not reassessed, approved, briefed or recorded.

CATZOC OMITTED

Depth and positional survey uncertainty are ignored without better local information.

STATIC ONLY

Squat, heel, wave response or density is excluded from a dynamic condition.

TIDE ASSUMPTION

Predicted tide is used despite known meteorological or local variation without assessment.

Past observations for practice

Process

The squat tables displayed on the bridge did not match the squat calculations issued from the software required to be used for UKC assessment.

Human

The OP was not aware of how to apply allowance to UKC for barometric pressure. Operator's procedures gave specific guidance.

Human

The shallow depth alarm was set to 4.00 mtrs at echo sounder, which was not suitable as a higher setting for pre-warning, while the minimum UKC required was 0.70 mtrs at berth as per SMS.

Master's practical note

Recalculate one critical point independently. The most common weakness is not arithmetic but an input presented as exact despite survey, tide or squat uncertainty.

Equipment boundary and references

Equipment boundary: No universal CATZOC deduction is prescribed by OCIMF. The company policy and Master's documented assessment must use available survey and local information rationally.

References

OCIMF SIRE 2.0 Question Library Part 1, Version 1.0, Question 4.2.2
IMO Resolution A.893(21)
OCIMF Recommendations on Usage of ECDIS and Preventing Incidents
ICS Bridge Procedures Guide

Last reviewed: 2026-09-11