Question: What marine vessels navigated in the swamp where Trelleborg is located?
Context: Gushan Environmental Energy Limited (), is a biodiesel producer in China that was incorporated on May 16, 2006.  The Company produces biodiesel and by-products of biodiesel production, including glycerol, plant asphalt, erucic acid and erucic amide.  Biodiesel is a renewable, clean-burning and biodegradable fuel produced from a variety of feedstocks, such as vegetable oil, animal fat and recycled cooking oil.  Currently there are 5 production facilities located in Beijing, Shanghai, Mianyang in Sichuan province, Handan in Hebei province and Fuzhou in Fujian province, serving the northern, interior and southeastern regions of China respectively.  Biodiesel is used to fuel a range of diesel engines, typically after blending with diesel, including diesel engines found in trucks, mass transit vehicles, marine vessels and generators.  The by-products of its biodiesel production have commercial applications in the food, pharmaceutical and manufacturing industries.  The Company sells its products in China to direct users, including marine vessel operators, petroleum wholesalers and individual retail gas stations.  The Company primarily uses vegetable oil offal and used cooking oil to produce biodiesel.  It acquires the raw materials supply for each of its production facilities primarily from local suppliers. A Marine surveyor (including "Yacht & Small Craft Surveyor", "Hull & Machinery Surveyor" and/or "Cargo Surveyor") is a person who conducts inspections, surveys or examinations of marine vessels to assess, monitor and report on their condition and the products on them, as well as inspects damage caused to both vessels and cargo.  Marine surveyors also inspect equipment intended for new or existing vessels to ensure compliance with various standards or specifications.  Marine surveys typically include the structure, machinery and equipment (navigational, safety, radio, etc.) and general condition of a vessel and/or cargo.  It also includes judging materials on board and their condition.  Because certifications and subsequently payments are processed only after the surveyor has expressed his or her satisfaction, a marine surveyor holds a prestigious position and is held with much regard in the shipbuilding industry.  Marine Surveyors are highly qualified and technically sound and are usually selected after thorough evaluation procedures as vessels ranging from small ferries to enormous crude oil carriers and cruise liners are approved to sail into the high seas based purely on their judgement,competence and integrity. A marine chemist is an environmental, occupational safety and health professional who is a trained professional who is responsible for ensuring that repair and construction of marine vessels can be made in safety whenever those repairs might result in fire, explosion, or exposure toxic vapors or chemicals.  By virtue of his or her training, experience, and education, the Marine Chemist is uniquely qualified as a specialist in confined space safety and atmospheric sampling or monitoring. The Trelleborg Parish (Swedish: "Trelleborgs församling" ) is a parish belonging to the Diocese of Lund in the Church of Sweden and encompasses Trelleborg Municipality in Sweden.  The main church is the church of Saint Nicholas located in Trelleborg.  The parish covers a population of 22 807 people (2003). The Common Marine Inspection Document (CMID) (IMCA M 149) is a free to use marine inspection format provided by the International Marine Contractors Association for the inspection and audit of marine vessels involved in the offshore industry.  The inspection's purpose is to establish that a particular vessel is safe to work aboard, will not place anybody working on or around the vessel in danger and will not cause any harm to the environment.  The inspection also ensures that all mandatory certification for the vessel and its operations are up to date. The Trelleborg (or Trælleborg) west of Slagelse on the Danish island of Zealand, is one of seven Viking ring castles discovered as of 2014.  In its day, the fortress was situated on a peninsula that jutted into the swampy area between two rivers.  The swamp was connected to the Great Belt by a lake that at its time could be navigated by Viking ships.  Trelleborg is believed to have been ordered by King Harald Bluetooth in the year 980 AD and it might have commanded the Great Belt and its sea traffic, between the islands of Zealand and Funen. The Craft Identification Number (CIN) or Hull Identification Number (HIN), standardised as EN ISO 10087:2006, is a permanent unique fourteen-digit alphanumeric identifier issued to all marine vessels in Europe.  The numbering system is mandated by the European Recreational Craft Directive and descended from the American Ship Hull number system.  Larger vessels over 300 gross tonnes also receive a permanent international IMO ship identification number, and European vessels over 20 metres receive a permanent ENI number. Viking ships were marine vessels of unique design, built by the Vikings during the Viking Age. Bennett Offshore, L.L.C., is an independent naval architecture, design and consulting firm founded in 1997 by William T. Bennett, Jr., to deliver engineering services to the offshore industry.  Bennett headquarters are located in Houston, Texas, and the company has an engineering office in New Orleans, Louisiana.  Bennett Offshore provides traditional naval architecture, structural, mechanical and electrical engineering as well as hydrodynamics and other marine- and offshore-related services.  In addition, the firm is involved in design, modification, and construction supervision of marine vessels, liftboats and other offshore mobile drilling and production units.  Bennett Offshore worked in collaboration with the Offshore Technology Development group of Keppel Offshore & Marine to design the ORCA series of self-propelled, self-elevating platforms. An oily water separator (OWS) (marine) is a piece of equipment specific to the shipping or marine industry.  It is used to separate oil and water mixtures into their separate components.  This page deals exclusively oily water separators aboard marine vessels.  They are found on board ships where they are used to separate oil from oily waste water such as bilge water before the waste water is discharged into the environment.  These discharges of waste water must comply with the requirements laid out in Marpol 73/78.  For information on more general oil water separators Oily Water Separators (general).
Answer: Viking ships