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Under keel clearance (UKC) is the term and calculations used in seafaring to ensure sufficient navigable water is available for ships at sea. It is most commonly described as the height and width of available water below the keel (hull of a ship). More simply, it can be described as how much water is left between the bottom of the ship and the seabed.

Master mariners should ensure there is sufficient minimum UKC for their ships and ports should ensure sufficient minimum UKC for the type and draft of ships due to arrive in the port. Ships typically calculate their UKC to meet criteria for ports to minimise the risk of maritime incidents. A minimum UKC value is determined, which includes a safety margin.

Methods of calculation

At a basic level, it is typically calculated in metres using the formula: Charted Depth − Draft -/+ Height of Tide = UKC. Ship masters and deck officers can obtain the depth of water from Electronic navigational charts. More dynamic or advanced calculations include safety margins for manoeuvring effects and squat.

Computer systems and software can be used to manage and calculate UKC for ships and ports. These include systems that dynamically manage UKC using models, forecasting and calculations.

The International Hydrographic Organization (IHO) sets a Standard for UKC Management for software and systems: S-129 Under Keel Clearance Management.

Uses and requirements

For US waters, the US Code of Federal Regulations require ships and their masters to calculate UKC based on the ship's deepest navigational draft.33 CFR 157.450 The regulations require the master to discuss the UKC calculation with the maritime pilot as the ship approaches US ports/waters.33 CFR 157.450

The Australian Maritime Safety Authority state that maintaining adequate UKC is important for safe navigation in the Torres Strait.

Inadequate UKC, caused by shallow water and squat may lead to ship groundings. In 2019, the UK Marine Accident Investigation Branch found that indequate UKC contributed towards the grounding of the ro/ro freight ferry MS Stena Performer.

Changes in water level may cause issues with adequate UKC for ships. For example, recent water level reductions in the Panama Canal have reduced UKC for ships meaning some ships are not able to transit the canal.

References

1. Gilardoni, Eduardo O.; Presedo, Juan P. (2017). Navigation in Shallow Waters. Livingston, Scotland: Witherby Publishing Group. p. 67. ISBN 978-1-85609-667-6.
2. ^ ECDIS Safety Settings and UKC Management. Livingston, Scotland: Witherby Publishing Group. 2017. ISBN 9781914993695.
3. ^ Weintrit, Adam (2009-06-02). Marine Navigation and Safety of Sea Transportation. Boca Raton : London: CRC Press. p. 484. ISBN 978-0-203-86934-5. OCLC 435419166.
4. "What Is Underwater Keel Clearance?". Marine Insight. Retrieved 4 April 2024.
5. "Simplified approach to operationalise UKC calculations Conference Paper". PIANC. Retrieved 4 April 2024.
6. ^ "All you ever wanted to know about Under Keel Clearance but were afraid to ask". Nautical Institute. Retrieved 4 April 2024.
7. ^ ECDIS Passage Planning and Watchkeeping. Livingston, Scotland: Witherby Publishing Group. 2023. p. 25. ISBN 9781856098168.
8. "Under Keel Clearance Technology Wins International Award". Maritime Executive. Retrieved 4 April 2024.
9. "Under Keel Clearance System Upgrade for Bunbury". Daily Cargo News. Retrieved 4 April 2024.
10. "OMC". International Harbour Masters Association. Retrieved 4 April 2024.
11. "Dynamic Draft and Under Keel Clearance". International Hydrographic Organization (IHO). Retrieved 4 April 2024.
12. "Under Keel Clearance Management System Fact Sheet". Australian Maritime Safety Authority. Retrieved 4 April 2024.
13. ^ "MAIB: Shallow Water Effects Contributed to Ro/Ro's Grounding". Maritime Executive. Retrieved 4 April 2024.
14. "Panama Canal water levels cause long-term concern". Riviera. Retrieved 4 April 2024.
15. "Panama Canal Drought Slows Cargo Traffic". The New York Times. Retrieved 4 April 2024.

• Nautical terminology
• Navigation
• Ship measurements