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What is a Vessel?
For a seaman to be classified as a seaman for puposes of the Jones Act, they must be injured on a vessel. What is a vessel was relatively easy to be defined before the oil and gas offshore exploration started in the 1970s. This site will track the development of case law in the United States as to what is a vessel. The imagination of engneers know no bounds when it comes to developing offshore structures to capture "Texas Tea". One such structure is the Semi-Sumbmersible: He re is a great story from Energy current outlining the history and development of the Semi-Submersible:
Semisubmersible
Semisubmersibles are floating mobile offshoe drilling units (MODUs) that are designed to drill in water depths beyond the capability of jackup drilling rigs, generally from 300 ft of water to 10,000 ft of water and greater. However, semisubmersibles have drilled in significantly shallower water where typically a jackup would operate. On the other end of the spectrum, semisubmersibles have drilled in water depths of about 10,000 ft.
Basic semisubmersible design
Most modern semisubmersibles are rectangular and float on pontoons with four or more columns connecting the pontoons to the hull. Some earlier designs were triangular and were similar in looks to the Transworld design submersibles. A few early designs utilized five support columns, and were known as a Pentagon design. Other designs utilized four large columns at the corners of the rig and two smaller columns on each side of the hull. The columns are usually cylindrical although one design utilized square columns and pontoons, primarily to reduce the cost of building the rig as only a few shipyards have the expertise, experience and equipment to roll steel into cylindrical braces and columns.
Station-keeping capabilities
Similar in looks to some submersibles, which are bottom-supported drilling units, semisubmersibles are ballasted and partially submerged to a predetermined depth. They are held on location with huge anchors that can weigh up to 10 tons each that are attached to large chains and cable from the rig to keep the rig stationary above the wellsite.
Other semisubmersibles are equipped with dynamic positioning (DP) equipment to keep the rig in position via computer controlled thrusters, or propellers. Geographical positioning systems (GPS) help keep the rig on location. Dynamically positioned rigs also usually have the capability to be moored over a wellsite with anchors and chains rather than in DP mode when drilling in shallower waters that don’t require using the rig’s DP mode. Using DP equipment is very expensive, especially for fuel costs, as engines and motors must constantly run in order to power the thrusters that keep the rig stationary over the wellsite.
Mobilizing to the wellsite and preparing to drill
Semisubmersibles can be either towed to a location or, if the unit is self-propelled, it can mobilize under its own power. The latter is seldom done due partly to the fact that semisubmersibles are top heavy when not in the drilling mode. However, over long distance tows, the rig’s power can be used to reduce the load on the towing tugs.
Once the unit is on location, the pontoons and portions of the columns are ballasted with seawater similar to the way a submersible would be ballasted to the seafloor. In the case of a semisubmersible, however, it is only partially submerged (hence, the name) and it floats above the wellsite. When partially submerged, only a portion of the columns are visible along with the rig’s hull, decks and drilling equipment. The pontoons are completely submerged.
When submerged, the columns provide a stable platform with minimal amount of movement as the waves pass below the hull and around the columns, essentially making the rig “invisible” to wave motions.
When the rig finishes drilling a well, the pontoons and columns are deballasted of seawater, the semisubmersible’s pontoons float to the surface and the unit is towed to the next site.
Semisubmersible generations
Semisubmersibles have been a staple of the industry’s deepwater drilling fleet since the mid-60s. The industry refers to various generations of semisubmersibles based partly on the rig’s age, its capabilities and its water depth. Defining a generation accurately is important for the contract drilling industry as a semisubmersible’s generation designation is used during drilling contract negotiations, fleet analyses and valuation and for various market studies and forecasts not only conducted by ODS-Petrodata but drilling contractors and others.
The advent of each new generation of semisubmersible came about following a lull in rig construction that resulted from an oversupply of semisubmersibles. Each subsequent generation offered significant technological advancements over the previous generation in terms of design and capabilities. Additionally, upgrades and modifications to existing semisubmersibles, for example, increasing its water depth rating or upgrading of equipment, could sometimes nudge a second generation unit into the third generation column since, while it may have been built in a second generation year, it was upgraded to compete with third generation semisubmersibles. That is a concept not always easily grasped.
Following an extensive industry survey in 1999, ODS-Petrodata provided a generation designation for every semisubmersible in the worldwide fleet, based generally upon year built but also considering the rig’s water depth capability and other parameters such as the variable deck load capacity. ODS-Petrodata formatted its designation using 2/3, 2/4, 3/4, etc. where the first number represents the rig’s generation in terms of the year it was built and the second number indicates the rig’s generation by capability. Hence, in the example above, that particular semisubmersible would be designated as 2/3.
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LEGAL COMMENT: By Steve Gordon
There are a few cases, mainly from the 5th Circuit holding that these structures are, in fact, vessels for prposes of applying tjje Jones Act.
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Jones Act - What is a Vessel?
