Some believe that the lights used in lighthouses are some of the brightest in the world, but lighthouse manager Warren Clarke describes those used by Trinity House as the most effective lights that are available right now.
Trinity House is a general lighthouse authority (GLA) that maintains more than 60 lighthouses in England, Wales, the Channel Islands and Gibraltar. Of these stations, Alderney uses lights with a range of 12 nautical miles (nm) at a height of 37 metres, while Bishoprock has lights that can reach 20nm at 44 metres.
At the older stations, the set-up includes a 3.5t optic comprising glass lenses and prisms mounted in a phosphor bronze frame. These can rotate on a mercury bath with a light fitting inside the middle of the optic to produce ranges of up to 26nm. The light source is fixed and the lantern rotates around the light source, generating the required number of flash beams. The mariner may be able to see the beam sweeping across before and after a flash from the optic. The speed of rotation defines the sequence of flashes, called its ‘character’, that enables the mariner to identify the lighthouse correctly. Optic panels are arranged so the required flash character can be achieved when rotating at constant speed. These lighthouses can also produce a flash by turning the navigation light on and off in a ‘coded’ character. This process does not require a rotating optic, but there are often drum lenses with a flashing lamp that create a disc of light that shines in all directions.
How are the lighthouses powered? The majority of Trinity House lighthouses are battery-powered, and they are recharged using mains power, solar, wind and generators. Some of the older designs are 240V systems which require an installed generator for back-up supply.
At the modernised stations, there is a main light and standby light. Each is powered from its own dedicated 24V DC battery system. Chargers are used to keep the batteries at full capacity. In the event of a mains electrical failure, each battery will sustain the lights for 48 hours, or 120 hours on offshore stations. This period allows the mains electricity to be reestablished while also providing sufficient time for technicians to attend the site in the event of an equipment failure.
Some lighthouses offer 24-hour lights, while some stations have day/night sensors built into the system. “As we get to twilight, the light comes on, and that sends a signal to our Harwich monitoring centre.”
Remote monitoring
The Harwich site in Essex also provides overnight and weekend monitoring for lighthouses managed by the Northern Lighthouse Board.
The Northern Lighthouse Board is responsible for operating and maintaining 208 lighthouses in Scotland and the Isle of Man. Its ships Polestar and Pharos carry out buoy work, deliver stores and supplies to lighthouses and inspect navigation aids on oil and gas rigs.
Craig Pake, planning engineer at Northern Lighthouse Board, says most stations come with a main and reserve lamp providing a range up to 22nm and emergency optics that have a range of nine.
“A lot of sites have LED’s sitting on top of another one – known as a bi-form (pictured, top right) – and both will flash. If one light goes out, it will still meet the range, so you can then get out and effectively repair the faulty one.”
The lights have photoelectric cells that can determine whether the flash character is working correctly. When faults arise on LED lights, technicians can use a handheld device on site to set the flash character of the replacement light.
Meanwhile, a telemetry system carries out remote monitoring at sites, currently using the PSTN and GSM networks. However, Pake briefly touches upon how the organisation is transitioning to an IP-based system accessed via a web browser. This promises to provide more reliable communications 24/7, while also expanding the number of inputs and outputs that enable users to carry out remote commands.
“For example, some of the lights allow you to send commands like starting and stopping an engine or triggering a reset to start the optics again,” he adds.
Site visit challenges
Such developments are important because some of the lighthouses are in very remote locations that can take technicians a day or two to reach. The Northern Lighthouse Board has teams based in Edinburgh, Inverness, Oban, Orkney and Shetland, and use a computer-aided maintenance management system that determines when maintenance needs to be carried out.
“The technicians could be deployed at some sites for up to 12 days and the team need to take food with them to be self-sufficient,” Pake continues. “For some road-accessed sites, you can still be three to four hours away, so there is a need to stay in local hotels and guest houses.” Pake emphasises the importance of booking accommodation well in advance to stay ahead of reservations made by tourists.
Once on site, technicians must ensure the reliability of the optic system, change certain components on a yearly or biennial basis and make sure the battery cells and charging systems are healthy, as some of them have to be topped up with demineralised water.
At Trinity House, Clarke reveals that three teams intend to visit all stations twice a year to carry out planned maintenance in an “MOT-style check”.
“This will ensure that all the systems within the station are working to the original parameters,” he continues. “We also plan to make a second visit to the station if anything untoward arises, like faulty batteries, solar panels or chargers.”
Trinity House carries out technical visits that fall into planned maintenance, a category that covers aids to navigation while a separate category relating to corrective maintenance entails carrying out legislative checks such as the servicing of fire equipment. Both areas are covered by a set of inspection points that the authority usually carries out annually, but can vary depending on risk.
During these checks, additional work may be identified, and if the team have the resources and time to rectify the issue, a work order is raised and the work is completed during the trip. If the work requires additional resources, a work order is raised identifying the issue and setting a timeline for the repair to be carried out. The technical team would then return on a corrective maintenance visit to carry out any identified work.
Clarke explains that lighthouses with a short-range main light may only require single visit per year as they can be less complex, depending on the location. The inspection would be carried out with a bespoke set of inspection points recorded on Trinity House’s maintenance management system. The complexity of a lighthouse’s maintenance needs is determined by the risk associated with the coast area, as reviewed by the authority’s examiners committee.
For Clarke, however, the biggest maintenance challenge relates to the structure of seven offshore lighthouses that are located on rocks. “These 43-metre granite towers take an awful lot of money just to remain standing, and it’s expensive to get there because you can only access the sites via helicopter. We overcome these challenges by planning well ahead. Civil structures involve doing lots of little bits of work rather than letting them get to a point where they start to fall into disarray.
BOX: Getting the right range
Clarke explains that Trinity House offers light ranges of six to 26 miles for lighthouses, depending on the risks in the surrounding sea area. When the GLA engineers its stations, the Examiners Committee of the General Lighthouse Authority reviews the range and character requirements of the lighthouse.
“The examiners are able to scrutinise far more traffic data to ensure a reduction in lighthouse range does not increase the risk to the local mariner,” Clarke adds.
To modify the range of light, Trinity House uses shaded sectors to identify specific maritime hazards which are described on Admiralty charts. At some lighthouses, it utilises blank sectors.
Where a sector is part of navigational requirements, it generally reuses the existing optic arrangement. Calculations are carried out to identify the best light source for the specific optic. Standard control equipment is designed around the light source to provide the required character and range. Once installed, a physical light measurement is conducted to ensure the calculated range can be realised.