Author: John P. Meskell, John Meskell Marine Electronics
Ireland is an island nation with a long and established history in the shipping industry. Merchant shipping is an international business engaged in transporting in excess of 70% of world trade globally. The modern ship is now like a floating village, comprising all the essential elements necessary to maintain a safe, healthy and sustainable environment for her sea-going inhabitants.
These floating villages contain many systems, including: electrical power generation and distribution, sewage treatment, fresh-water production and treatment facilities, and main engine with power train and propulsion.
[caption id="attachment_15666" align="alignright" width="1009"] Fig 1: Below-deck propulsion plant with auxiliary machinery and services (click to enlarge)[/caption]
In recent years, there have been huge advancements in the field of micro-electronics, electronics and hybrid automation and control including hydraulic and pneumatic systems. The typical engine room layout (see Fig 1) indicates how far we have evolved from the days of wind power. Recent developments in marine power train/propulsion indicate that diesel electric systems are replacing conventional diesel engines, which in most cases had superseded steam turbine engines.
The larger vessels are fitted with engine capacities in excess of 50,000 HP/36 megawatt. The more conventional propulsion systems consist of power from variable-speed engines, driving a propeller shaft with a fixed propellers or ‘screw’. Many systems now employ constant-speed engines driving a shaft with variable pitch propellers, allowing the use of shaft alternators while at sea. Typically, the propellers on a large vessel would rotate at between 60 RPM and 120 RPM – as opposed to aircraft props, which require an extremely high RPM.
PROPULSION AND STEERING
Many modern vessels, especially the larger cruise ships, are now using rotatable Pod-type systems, which control not only the propulsion, but also the steering of the vessel. These Pods replace the propellers and rudders – generating the thrust in a variable 360° plane, allowing optimum manoeuvrability. Other advantages, including a decreased stopping distance and greater fuel efficiency for the vessel, mean that the implementation of these systems has increased dramatically in recent years. Electric bow and stern thrusters (300 kW) are in common use to improve manoeuvrability, dispensing with the requirement for costly tug-boat assistance while docking.
[caption id="attachment_15668" align="alignright" width="1204"] Fig 2: Integrated engine-room control system (click to enlarge)[/caption]
All main engines, auxiliary and service systems are remotely monitored and controlled from the bridge and engine control room (ECR). A sophisticated alarm system with appropriate transducers ensures safe and efficient functioning. System control is via complex integrated automation networks. Where necessary, full dynamic positioning systems (DPS) are available for vessels, typically for drilling, seismic and survey operations when the vessel is required to be absolutely stationary.
Merchant shipping is a genuinely international business engaged in transporting in excess of 70% of world trade globally. The IMO (International Maritime Organisation – a specialised group within the United Nations) is the regulatory body that ensures adherence to safe work practices, equipment carriage requirements, and educational and training standards within the industry.
The IMO ensures compliance with the Safety of Life at Sea Convention (SOLAS) and the Standards of Training and Certification of Watchkeeping Officers (STCW 1995). The SOLAS Convention was brought into being as a result of inadequacies in lifeboat numbers and emergency equipment that were shown to be inadequate when the RMS Titanic sank in 1912.
The SOLAS Convention, which is primarily concerned with equipment fittings, was fully implemented in 1965. The complexity of electrical, electronic and mechanical systems demand skilled, competent and educated engineers; STCW Convention ensures uniformity of training and education across this international industry.
NAVIGATION AND COLLISION AVOIDANCE SYSTEMS
Until the 1980s, mariners relied on sun and star sightings using sextants to ascertain their position. Some radio position fixing systems were used such as Loran, Omega and Decca, with direction-finding equipment used for coastal navigation.
Satellite position fixing systems (GPS – global positioning system) developed in the 1970s were primarily for US military use, but were later made available for use in marine engineering within commercial shipping. The more accurate differential GPS system (DGPS) is now widely used, with position fixing to within 10cm.
A modern bridge will contain the following aids to navigation and collision avoidance systems: primary radars, electronic chart display & information systems (ECDIS), position fixing, gyro heading, Doppler speed and distance measuring, automatic identification system transponders, autopilot and speed control, anemometers, depth sounders/sonar and other aids.
All the above can be fully integrated into controllable, user-friendly display and control systems for use by the navigator. In various forms, these make up the modern NACOS (navigation and command system) on a ship.
[caption id="attachment_15670" align="alignright" width="838"] Fig 3: Typical arrangement of an Integrated Navigational and Command System – L3 SAM Electronics 'Platinum' (click to enlarge)[/caption]
In addition to its use as a navigation aid, radar is the primary method for collision avoidance at sea. The two types of radars in general use are X-Band (9.3 to 9.5 GHz, 3cm λ) and S-Band (3 GHz, 10cm λ). Larger vessels like cruise ships can have several radars installed, with some smaller ones near the bow or stern to aid docking. All these can be ‘inter-switched’ or accessible on any radar display via hardware, software and networking of the systems. The latest systems allow the echoes from multiple radar transmitters to be plotted on a single display.
Radar principles are based on transmitted pulses being reflected by distant targets. The acronym RADAR denotes ‘radio aid to direction and range’. Thus, these echoes reflected by other ships, buoys or coastlines may be plotted manually on a radar screen/indicator display, providing ‘track’ information for echoes that can offer a range, bearing, position and ‘closest point of approach’ relative to the ship. These plots can also be done automatically by built-in automatic radar plotting aid functionality.
There are many prerequisites for the plotting of targets on radars; these include the radar being interfaced with type-approved sensor interfaces producing gyro heading, speed log, GPS or the more accurate DGPS positioning devices. Built-in test equipment is used to indicate the functional status of the equipment and diagnostic programmes are included to aid serviceability.
X-Bands transmit with 12.5kW or 25kW power outputs, producing ranges of approximately 50 nautical miles. Range and definition is determined by scanner/antenna consideration.
Most radars operate with selectable transmitted pulse-lengths for varying ranges (short, medium and long). When selected, the transmitted pulse length (time, µs) and PRF (pulse repetition frequency, Hz) of the transmitted signal will vary. Typical PRF/pulse length combinations are 1000Hz at 0.30 µsec (SP) or 500Hz PRF with 0.90 µsec pulse length (LP).
The long pulse (LP) combination permits a longer time for the signal echoes to return from a longer distance target before the next pulse is transmitted via the rotating scanner (usually at around 24 RPM). The radars plot the echoes on the multi-functional displays.
S-Band radars are also carried, because they provide enhanced performance in adverse weather conditions due to a lower transmission frequency, and longer wavelength for increased target range detection. However, theses characteristics result in lower definition of targets on the radar display.
The main function of any radar is to aid safe navigation, but modern systems are now complex and are integrated with other bridge systems such as ECDIS and to provide a radar overlay on the approved ECDIS charts.
Autopilot and speed control can be performed via the radar display with the required integration, where pre-defined and approved tracks and routes can be activated by the touch of a button. These features are designed to aid the navigator, reducing the workload on watchkeepers while providing more economic and efficient vessel management by constantly using adaptive algorithms to update the system.
In the second article of this two-part series, John P. Meskell outlines modern marine communications – such as automatic identification systems, voyage data recording, and vessel traffic systems – and takes a closer look at Ireland’s marine environment.