seafaring Seamanship is the skill, art, competence (human resources), competence, and knowledge of operating a ship, boat or other craft on water. The'' Oxford Dictionary of English, Oxford Dictionary'' states that seamanship is "The skill, techniques, o ...

, under keel clearance (UKC) is the vertical distance between

seabed The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as seabeds. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...

and the

keel The keel is the bottom-most longitudinal structural element of a watercraft, important for stability. On some sailboats, it may have a fluid dynamics, hydrodynamic and counterbalancing purpose as well. The keel laying, laying of the keel is often ...

hull Hull may refer to: Structures * The hull of an armored fighting vehicle, housing the chassis * Fuselage, of an aircraft * Hull (botany), the outer covering of seeds * Hull (watercraft), the body or frame of a sea-going craft * Submarine hull Ma ...

of a

ship A ship is a large watercraft, vessel that travels the world's oceans and other Waterway, navigable waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research and fishing. Ships are generally disti ...

. It is used to ensure sufficient

navigable A body of water, such as a river, canal or lake, is navigable if it is deep, wide and calm enough for a water vessel (e.g. boats) to pass safely. Navigability is also referred to in the broader context of a body of water having sufficient under ...

water is available for ships at sea.

Master mariner A master mariner is a licensed mariner who holds the highest grade of licensed seafarer qualification; namely, a master's license. A master mariner is therefore allowed to serve as the captain (nautical), master of a merchant ship for which natio ...

s should ensure there is sufficient minimum UKC for their

ships A ship is a large vessel that travels the world's oceans and other navigable waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research and fishing. Ships are generally distinguished from boats, ...

;

ports Ports collections (or ports trees, or just ports) are the sets of makefiles and Patch (Unix), patches provided by the BSD-based operating systems, FreeBSD, NetBSD, and OpenBSD, as a simple method of installing software or creating binary packages. T ...

should ensure sufficient minimum UKC for the type and

draft Draft, the draft, or draught may refer to: Watercraft dimensions * Draft (hull), the distance from waterline to keel of a vessel * Draft (sail), degree of curvature in a sail * Air draft, distance from waterline to the highest point on a v ...

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. The minimum UKC determined includes a safety margin.

Methods of calculation

At a basic level, it is typically calculated in metres using the formula: :UKC = Charted Depth −

Draft Draft, the draft, or draught may refer to: Watercraft dimensions * Draft (hull), the distance from waterline to keel of a vessel * Draft (sail), degree of curvature in a sail * Air draft, distance from waterline to the highest point on a v ...

-/+ Height of

Tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables ...

Ship masters and deck officers can obtain the depth of water from

Electronic navigational chart An electronic navigational chart (ENC) is an official database created by a national hydrographic office for use with an Electronic Chart Display and Information System (ECDIS). ECDIS and ENCs are the primary means of electronic navigation on c ...

s. 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 The International Hydrographic Organization (IHO) (French: ''Organisation Hydrographique Internationale'') is an intergovernmental organization representing hydrography. the IHO comprised 102 member states. A principal aim of the IHO is to ...

(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 In the law of the United States, the ''Code of Federal Regulations'' (''CFR'') is the codification of the general and permanent regulatory law, regulations promulgated by the executive departments and agencies of the federal government of the ...

require ships and their masters to calculate UKC based on the ship's deepest navigational draft. The regulations require the master to discuss the UKC calculation with the

maritime pilot A maritime pilot, marine pilot, harbor pilot, port pilot, ship pilot, or simply pilot, is a mariner who has specific knowledge of an often dangerous or congested waterway, such as harbors or river mouths. Maritime pilots know local details s ...

as the ship approaches US ports/waters. The

Australian Maritime Safety Authority Australian Maritime Safety Authority (AMSA) is an Australian statutory authority responsible for the regulation and safety oversight of Australia's shipping fleet and management of Australia's International Maritime Organization, international ...

state that maintaining adequate UKC is important for safe navigation in the

Torres Strait The Torres Strait (), also known as Zenadh Kes ( Kalaw Lagaw Ya#Phonology 2, �zen̪ad̪ kes, is a strait between Australia and the Melanesian island of New Guinea. It is wide at its narrowest extent. To the south is Cape York Peninsula, ...

. Inadequate UKC, caused by shallow water and squat may lead to

ship grounding Ship grounding or ship stranding is the impact of a ship on seabed or waterway side. It may be intentional, as in beaching (nautical), beaching to land crew or cargo, and careening, for maintenance or repair, or unintentional, as in a marine ac ...

s. In 2019, the UK

Marine Accident Investigation Branch The Marine Accident Investigation Branch (MAIB) is a UK government organisation, authorised to investigate all maritime accidents in UK waters and accidents involving UK registered ships worldwide. Investigations are limited to establishing ca ...

found that indequate UKC contributed towards the grounding of the ro/ro freight ferry

MS Stena Performer MS ''Performance'' is a ro-ro freight ferry that entered service with Seatruck Ferries April in 2012. She currently operates for CLdN. The vessel was on charter to Stena Line for 6 years from Seatruck Ferries, during which she was named ''Stena ...

. Changes in water level may cause issues with adequate UKC for ships. For example, recent water level reductions in the

Panama Canal The Panama Canal () is an artificial waterway in Panama that connects the Caribbean Sea with the Pacific Ocean. It cuts across the narrowest point of the Isthmus of Panama, and is a Channel (geography), conduit for maritime trade between th ...

have reduced UKC for ships meaning some ships are not able to transit the canal.

References

{{Ship measurements Nautical terminology Navigation Ship measurements Vertical position