Air draft

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The deck of the Allanburg Bridge on Canada's Welland Canal typically rests only a few metres above the water level. When a ship approaches, the deck is raised to provide sufficient air draft (or draught) for the vessel to pass through. This bridge was involved in a collision with a lake freighter in 2001 as a result of lowering the span before the ship fully cleared the bridge. Allanburg Bridge.jpg
The deck of the Allanburg Bridge on Canada's Welland Canal typically rests only a few metres above the water level. When a ship approaches, the deck is raised to provide sufficient air draft (or draught) for the vessel to pass through. This bridge was involved in a collision with a lake freighter in 2001 as a result of lowering the span before the ship fully cleared the bridge.

Air draft (or air draught) is the distance from the surface of the water to the highest point on a vessel. This is similar to the "deep draft" of a vessel which is measured from the surface of the water to the deepest part of the hull below the surface, but air draft is expressed as a height, not a depth. [1] [2]

Contents

Clearance below

The vessel's "clearance" is the distance in excess of the air draft which allows a vessel to pass safely under a bridge or obstacle such as power lines, etc. A bridge's "clearance below" is most often noted on charts as measured from the surface of the water to the under side of the bridge at the chart datum Mean High Water (MHW), [3] [4] a less restrictive clearance than Mean Higher High Water (MHHW).

In 2014, the United States Coast Guard reported that 1.2% of the collisions it investigated in the recent past were due to vessels attempting to pass underneath structures with insufficient clearance. [1]

Examples

Bridge of the Americas Bridge of the Americas.jpg
Bridge of the Americas

The Bridge of the Americas in Panama limits which ships can traverse the Panama Canal due to its height at 61.3 m (201 ft) above the water. The world's largest cruise ships, Oasis of the Seas, Allure of the Seas and the Harmony of the Seas will fit within the canal's new widened locks, but they are too tall to pass under the bridge, even at low tide (the two first ships are 72 m (236 ft), but do have lowerable funnels, enabling them to pass the 65-metre (213 ft) Great Belt Bridge in Denmark). New vessels are rarely built not clearing 65 m (213 ft), a height which accommodates all but the largest cruise and container ships.

The Suez Canal Bridge has a 70-metre (230 ft) clearance over the canal.

The Bayonne Bridge, an arch bridge connecting New Jersey with New York City, undertook a $1.7 billion modification to raise its roadbed to 66 m (217 ft). [5]

See also

Related Research Articles

Kiel Canal Canal in Germany

The Kiel Canal is a 98-kilometre-long (61 mi) freshwater canal in the German state of Schleswig-Holstein. The canal was finished in 1895, but later widened, and links the North Sea at Brunsbüttel to the Baltic Sea at Kiel-Holtenau. An average of 250 nautical miles (460 km) is saved by using the Kiel Canal instead of going around the Jutland Peninsula. This not only saves time but also avoids storm-prone seas and having to pass through the Danish straits.

Panama Canal Large artificial waterway in the Republic of Panama, connecting the Atlantic and Pacific Oceans

The Panama Canal is an artificial 82 km (51 mi) waterway in Panama that connects the Atlantic Ocean with the Pacific Ocean. The canal cuts across the Isthmus of Panama and is a conduit for maritime trade. One of the largest and most difficult engineering projects ever undertaken, the Panama Canal shortcut greatly reduces the time for ships to travel between the Atlantic and Pacific oceans, enabling them to avoid the lengthy, hazardous Cape Horn route around the southernmost tip of South America via the Drake Passage or Strait of Magellan and the even less popular route through the Arctic Archipelago and the Bering Strait.

Sea level Geographical reference point from which various heights are measured

Mean sea level (MSL) is an average level of the surface of one or more of Earth's bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datum – a standardised geodetic datum – that is used, for example, as a chart datum in cartography and marine navigation, or, in aviation, as the standard sea level at which atmospheric pressure is measured to calibrate altitude and, consequently, aircraft flight levels. A common and relatively straightforward mean sea-level standard is instead the midpoint between a mean low and mean high tide at a particular location.

Buoy Floating structure or device

A buoy is a floating device that can have many purposes. It can be anchored (stationary) or allowed to drift with ocean currents.

Waterway Any navigable body of water

A waterway is any navigable body of water. Broad distinctions are useful to avoid ambiguity, and disambiguation will be of varying importance depending on the nuance of the equivalent word in other languages. A first distinction is necessary between maritime shipping routes and waterways used by inland water craft. Maritime shipping routes cross oceans and seas, and some lakes, where navigability is assumed, and no engineering is required, except to provide the draft for deep-sea shipping to approach seaports (channels), or to provide a short cut across an isthmus; this is the function of ship canals. Dredged channels in the sea are not usually described as waterways. There is an exception to this initial distinction, essentially for legal purposes, see under international waters.

Nautical chart Topographic map of a maritime area and adjacent coastal regions

A nautical chart is a graphic representation of a sea area and adjacent coastal regions. Depending on the scale of the chart, it may show depths of water and heights of land, natural features of the seabed, details of the coastline, navigational hazards, locations of natural and human-made aids to navigation, information on tides and currents, local details of the Earth's magnetic field, and human-made structures such as harbours, buildings, and bridges. Nautical charts are essential tools for marine navigation; many countries require vessels, especially commercial ships, to carry them. Nautical charting may take the form of charts printed on paper or computerized electronic navigational charts. Recent technologies have made available paper charts which are printed "on demand" with cartographic data that has been downloaded to the commercial printing company as recently as the night before printing. With each daily download, critical data such as Local Notices to Mariners are added to the on-demand chart files so that these charts are up to date at the time of printing.

Bayonne Bridge Bridge between New Jersey and New York

The Bayonne Bridge is an arch bridge spanning the Kill Van Kull connecting Bayonne, New Jersey, with Staten Island, New York City. It carries New York State Route 440 (NY 440) and New Jersey Route 440. It is the fifth-longest steel arch bridge in the world, and it was the longest in the world at the time of its completion. The bridge is also one of four connecting New Jersey with Staten Island; the other two roadway bridges are the Goethals Bridge in Elizabeth and Outerbridge Crossing in Perth Amboy, and the rail-only span is the Arthur Kill Vertical Lift Bridge, all of which cross the Arthur Kill.

Panamax Class of ships of the maximum size that can pass through the original locks of the Panama Canal

Panamax and New Panamax are terms for the size limits for ships travelling through the Panama Canal. The limits and requirements are published by the Panama Canal Authority (ACP) in a publication titled "Vessel Requirements". These requirements also describe topics like exceptional dry seasonal limits, propulsion, communications, and detailed ship design.

A cargo ship or freighter is a merchant ship that carries cargo, goods, and materials from one port to another. Thousands of cargo carriers ply the world's seas and oceans each year, handling the bulk of international trade. Cargo ships are usually specially designed for the task, often being equipped with cranes and other mechanisms to load and unload, and come in all sizes. Today, they are almost always built by welded steel, and with some exceptions generally have a life expectancy of 25 to 30 years before being scrapped.

Bathymetry Study of underwater depth of lake or ocean floors

Bathymetry is the study of underwater depth of ocean floors or lake floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The name comes from Greek βαθύς (bathus), "deep", and μέτρον (metron), "measure". Bathymetric charts are typically produced to support safety of surface or sub-surface navigation, and usually show seafloor relief or terrain as contour lines and selected depths (soundings), and typically also provide surface navigational information. Bathymetric maps may also use a Digital Terrain Model and artificial illumination techniques to illustrate the depths being portrayed. The global bathymetry is sometimes combined with topography data to yield a Global Relief Model. Paleobathymetry is the study of past underwater depths.

Bridge of the Americas Road bridge in Panama spanning the Pacific entrance to the Panama Canal

The Bridge of the Americas is a road bridge in Panama, which spans the Pacific entrance to the Panama Canal. Designed by Sverdrup & Parcel, it was completed in 1962 at a cost of US$20 million, connecting the north and south American land masses. Two other bridges cross the canal: the Atlantic Bridge at the Gatun locks and the Centennial Bridge.

Chart datum Level of water from which depths displayed on a nautical chart are measured

A chart datum is the water level that depths displayed on a nautical chart are measured from. A chart datum is generally derived from some phase of the tide. Common chart datums are lowest astronomical tide and mean lower low water. In non-tidal areas, e.g. the Baltic Sea, mean sea level (MSL) is used.

Suezmax Ship size ceiling capable to pass through Suez Canal

"Suezmax" is a naval architecture term for the largest ship measurements capable of transiting the Suez Canal in a laden condition, and is almost exclusively used in reference to tankers. The limiting factors are beam, draft, height, and length.

<i>Oasis</i>-class cruise ship Class of Royal Caribbean International cruise ships

The Oasis class is a class of Royal Caribbean International cruise ships. The first two ships in the class, Oasis of the Seas and Allure of the Seas, were delivered respectively in 2009 and 2010 by STX Europe Turku Shipyard, Finland. A third Oasis-class vessel, Harmony of the Seas, was delivered in 2016 built by STX France, and a fourth vessel, Symphony of the Seas, was completed in March 2018. As of April 2019, the fifth Oasis-class ship, Wonder of the Seas, is under construction. A sixth unnamed ship has also been ordered by the company. The first two ships in the class, Oasis of the Seas and Allure of the Seas, are slightly exceeded in size by the third ship, Harmony of the Seas, while Symphony of the Seas is the world's largest cruise ship. Wonder of the Seas, due to be completed in 2022, is planned to be larger than Symphony of the Seas. As of early 2019, all ships of the class rank as the world's largest passenger ships.

Port of New York and New Jersey Port

The Port of New York and New Jersey is the port district of the New York-Newark metropolitan area, encompassing the region within approximately a 25-mile (40 km) radius of the Statue of Liberty National Monument. It includes the system of navigable waterways in the New York–New Jersey Harbor Estuary, which runs along 650 miles (1,050 km) of shoreline in the vicinity of New York City and northeastern New Jersey, as well as the region's airports and supporting rail and roadway distribution networks. Considered one of the largest natural harbors in the world, the port has become the second busiest port by tonnage in the United States as of 2019, and the busiest on the East Coast.

Draft (hull) Vertical distance between the waterline and the bottom of the hull (keel)

The draft or draught of a ship's hull is the vertical distance between the waterline and the bottom of the hull (keel). Draft determines the minimum depth of water a ship or boat can safely navigate.

<i>Oasis of the Seas</i> Cruise ship

Oasis of the Seas is a cruise ship operated by Royal Caribbean International. She is the first of her class, whose ships are the largest passenger ships in the world. Her hull was laid down in November 2007 and she was completed and delivered to Royal Caribbean in October 2009. At the time of construction, Oasis of the Seas set a new capacity record of carrying over 6,000 passengers. The first of her class, she was joined by sister ships Allure of the Seas in December 2010, Harmony of the Seas in May 2016, and Symphony of the Seas in April 2018. Oasis of the Seas conducts cruises of the Caribbean from her home port of PortMiami in Miami, Florida.

Vertical datum Reference surface for vertical positions

A vertical datum, altimetric datum, or height datum is a reference surface for vertical positions, such as the elevations of Earth features including terrain, bathymetry, water level, and man-made structures. Commonly adopted criteria for a vertical datum include the following approaches:

Rendsburg High Bridge

The Rendsburg High Bridge is a railway viaduct on the Neumünster–Flensburg line that also serves as a transporter bridge. The bridge crosses the Kiel Canal at Rendsburg in the German state of Schleswig-Holstein. It is federally owned through the Federal Water and Navigation Administration that also owns and runs the canal.

Shipwrecking Event causing a ship to wreck

Shipwrecking is an event that causes a shipwreck, such as a ship striking something that causes the ship to sink; the stranding of a ship on rocks, land or shoal; poor maintenance; or the destruction of a ship either intentionally or by violent weather.

References

  1. 1 2 "Marine Safety Alert 090-14: AIR DRAFT IS CRITICAL!" (PDF) (Press release). United States Coast Guard Inspections and Compliance Directorate. 2014-09-09. Retrieved 2015-02-15.
  2. 2104 Connecticut Boater's Guide (PDF). State of Connecticut Department of Energy and Environmental Protection. p. 60. Retrieved 2015-02-15.
  3. See: NOAA Navigation Chart #12335, Hudson and East Rivers, Governors Island to 67th Street, Revised October 1, 2019, "HEIGHTS: Heights in feet above Mean High Water"
  4. See: U.S. Coast Pilot 5, Chapter 8, p. 354, Structures across the Inner Harbor Navigation Canal, New Orleans, 15 December, 2019, "Vertical clearance measured at Mean High Water"
  5. Bayonne Bridge rededication ceremony marks end of $1.7 billion project