FOUR STROKE DIESEL ENGINE WÄRTSILÄ 46F
2. Any product obtained by distilling petroleum and condensing the vapours
Direct-printing telegraphy – Automated telegraphy techniques which comply with the relevant recommendations of the International Radio Consultative Committee (CCIR), (SOLAS).
Direction of rotation of a propeller – When viewed from astern, if the propeller revolves in a clockwise direction when going ahead, it is known as right-handed. If in an anti-clockwise direction, it is left-handed.
Disabled ship – A damaged or impared vessel not able proceed by its own.
Disc grinder – Any machine that grinds by the action of a rotating disc.
Discharge – Any release from a ship including any escape, disposal, spilling, leaking, pumping, emitting or emptying.
Discharge book – An essential document for officers and seamen as it serves an official certificate confirming their sea experience in the employment time.
Discharges – Any piping leading through the ship sides for conveying bilge water, cooling water, drains, etc.
Discontinuity – An interrption of the typical structure of a material, such as lack of homogeneity in its mechanicall, metallurgical, or physical characteristics. A discontinuity is not necessarily a defect.
Discreet Security Alert System – The purpose of this system is to send a covert signal from a ship which will be not obvious to anyone on the ship who is not aware of the alert system.
It is of use therefore in circumstances where a ship wishes to inform a person ashore of a problem with a minimum number of persons on board aware of the action. Besides the security alert function the DSAS can also be used to locate the ship throughout the world in a reliable manner.
Disembark – Refers to any time that the crew leave the ship, be it a port call or final destination.
Displacement – It is the weight of water displaced by this vessel at any waterline. It is the product of the volume of its underwater portion and the density of the water in which it floats.
Displacement curve – A curve showing the displacement of a vessel in fresh or salt water at any draft.
Displacement pump – A pump operating by the reduction or increase in volume of a space by mechanical action which physically moves the liquid or gas.
Displacement vessel – A craft that is supported by the buoyancy of the water it displaces.
Displacement water – Water added to the separator bowl to displace the oil and to ensure there is no loss of oil at sludge discharge.
Display – Means by which a device presents visual information to the navigator, including conventional instrumentation.
Dissolved gases – Any gas present in water. It may be released when boiled.
Dissolved solids – Any impurities existing in pure water either produced by an evaporator or used as boiler feed water.
Distillate
Diving Distortion – The effects of welding on a metal plate. It may appear as shrinkage or an angular
twisting. Distortion of steel structures caused by welding and other thermal processes can be assigned to three main causes.
The first is the inherent stresses in the steel received from suppliers. These stresses are a result of heating, rolling and cooling of steel plates in the steel mills. Other causes may include the handling and storage of the plates during shipment to the shipyard and also while in storage prior to production. The inherent stresses may be relieved by cold rolling of the plates, but this may not completely eliminate them. In case of plates below 8mm thickness, cold rolling is not very effective.
The second cause is the distortion directly related to the thermal processes. If the plate is heated quickly, as during cutting or welding, the steel expands. When the plate cools slowly, the cooling causes schrinkage.
The third cause of distortion is an outcome of the management of the overall production process. This includes not only strict adherence to the correct welding procedures, but also the correct alignment of structural parts. Furthermore, it is essential to manage the correction of incipient distortion as it occurs during the assembly.
Distress – A term used when a ship requires immediate assistance.
Distress alert – A radio signal from a distressed automatically directed to a RCC giving position, identification, course and speed of the vessel as well as the nature of distress.
Distress signal – An urgent signal for help assistance.
Distributed load – A load that acts over a part or the whole of the surface of the structure.
Distribution – Electricity supply to various items of equipment, often at different voltages.
Distribution board – A grouping of electrical equipment in a distribution system, which supplies minor items such as lighting. It is supplied from a section board.
Disturbance – Any change inside or outside a control system which disturbs the equilibrum.
Diver – A person who dives, especially one who works under water using a diving-suit.
Diver lock-out compartment – A compartment within an underwater system or vehicle provided with internally pressurizing capability to transfer a diver to the work site from the submersible and back.
Diverter – A type of blowout preventer used on an oil rig to divert fluid safely from well under “kick” or rapid pressure rise condition.
Diving – The offshore industry is heavily dependant on diving operations. Air diving is used for the inspection and repair programmes carried out in shallow waters. For depths of more than 50m saturation diving is necessary. Safe diving operations require sophisticated support systems, such as large pressure chambers to allow the divers to remain under deep water pressure while on board.
Saturation divers live in an onboard accommodation chamber which is pressurised to several times atmospheric pressure for up to a month at a time, traveling to and from their work place at the sea bed in a similarly pressurised diving bell. At the end of their time on board they decompress slowly, allowing the absorbed gasses saturated within their tissues by the pressure, to gradually dissipate before exiting the chamber to normal atmosphere. Existing under pressure for extended periods negates the need for prolonged decompression at the end of each dive.This makes deep water diving practical, since it is not necessary to depressurize in between working spells. Diving support vessels are intended as a base for diving operations offshore and are fitted with all equipment necessary for safe deep water diving operations.
Further reading: “Offshore Engineering” by Agnus Mather, www.witherbys.com
Diving bell
Diving bell – A manned, non-self-propelled submersible tethered unit consisting of at least one chamber internally pressurized in order to allow a diver to be transported to and from an underwater site. It is secured to the diving support vessel by a steel cable and an umbilical provides the occupants with breathing gas, heated water, electrical power and communication facilities.
Diving support vessel (DSV) – A vessel provided with diving equipment and used for underwater work such as the maintenance and inspection of mobile platforms, pipelines and their connections, well-heads, etc. Today’s DSV is a highly sophisticated vessel that may be of mono, multi-hull or semi-submersible construction. The DSV is fitted with a moonpool – a hole in the middle of the vessel open to the sea – through which divers, remotely-operated vehicles and other equipment is passed to and from the worksite.
These vessels may also have A-frame at the stern, used for raising and lowering heavy pieces of equipment, including manned submersibles, into the water.
These vessels can maintain an almost exact position over the worksite during these operations. In order to accomplish this, they have fitted with very sophisticated positioning equipment.
Diving Support Vessel SEVEN ATLANTIC
According to Holland Shipbuilding June 2009
The SEVEN ATLANTIC, delivered by IHC Merwede in 2009 to Subsea 7, is one of the largest and most capable diving support vessels in the world. The 24-person saturation diving system includes four 3-man twin lock living chambers, two 6-man twin lock decompression chambers and two horizontal transfer under pressure chambers (chambers are 2.4m internal diameter). The system is designed to comply with Norwegian NORSOK requirements, and features much improved living conditions compared to previous systems.
The diving system can be divided at the centreline to allow for two crews working at different depths. From their living quarters, on-shift divers can access either of two saturation dive bells through two large transfer-underpressure chambers without disturbing the off-shift divers.
Picture courtesy of IHC Merwede
Diving system The diving bells have 7m3 internal capacity and are launched through two athwartships moonpools, positioned near the minimum motion point of the vessel. A comprehensive system of mechanical handling aids is fitted to support saturation and air diving operations, including port and starboard T bars, A-frames, hose reels, tugger winches and umbilical management hoop booms (20m reach from ship side). Two hyperbaric lifeboats are provided (one port and one starboard).
The divers breathe a helium-oxygen mixture for the entire work shift – up to 2-3 weeks.
Below the diving installation is a huge storage area for pressure vessels with helium/oxygen mixture. Some of the oxygen bottles are stored on deck for fire safety reasons. As helium is a costly gas, it is carefully retrieved from the divers’ exhaled air and recycled back to storage.
SEVEN ATLANTIC is designed to meet DP3 positioning class, taking into account one failure – including fire and flooding – and will not interfere with the vessel’s station keeping, in this particular case supporting diving in weather conditions of 4.5 m significant wave height.
This particularly demanding requirement also influenced the decision to opt for three engine rooms with each two diesel-generator sets and three switchboards, located in fire
& flooding separated rooms. With regard to the distribution through the main high voltage switchboard, there are vital separations between the generator fields by means of coupled circuit breakers.
The power plant comprises six Wärtsilä 7L32 engines, each driving a 3360kVA Van Kaick generator, generating 6,6 kV (mains voltage). The propulsion installation runs on marine gasoil. It provides power for propulsion, dive systems, crane activities and other consumers.
The entire propulsion/thruster package consists of three Wärtsilä fixed pitch propellers in azimuthing nozzles aft, each driven by an Indar propulsion squirrel cage motor with a shaft power of 2950kW. Each motor is controlled through a custom-designed and built direct water cooled frequency drive. Forward in the ship two electrical retractable Wärtsilä azimuth thrusters are provided, each with a shaft power of 2400kW. Control and power supply are again provided through a similar frequency drive for each thruster. All thrusters are equipped with a propeller nozzle to increase the thrust and to minimize the chance of fouling a wire or umbilical. Additionally, there is a transverse tunnel thruster in the bow with a shaft power of 2200 kW, bringing the total installed propulsion power to an impressive 15,850kW.
The SEVEN ATLANTIC is the first IHC Merwede vessel built under comfort class notation CAC(2). This notation imposes stringent noise levels on the crew quarters. These were achieved by placing the cabins in the accommodation block outside the forecastle and by adopting floating floors. In addition , a visco-elastic damping treatment is applied to the hull and bulkheads in the tunnel bowthruster room, which is a major source of noise during DP operations.
Length, oa: 144.79m, Length, bp: 128.96m, Breadth, mld: 26.00m, Depth to main deck:
12.00m, Draught design: 7.00m, Deadweight: 8700dwt, Trial speed: 13.6 knots, Occupants:
150 persons.
Diving system – Compressed air or gas mixture saturation system for the conduct of diving operations. Surface compression chamber, diving bell, handling system and fixed gas storage facilities are main components of a saturation diving system.
Dock –
1. A place where a ship can be moored. A wet dock is a port area isolated from tidal