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Seafaring A – Z Alphabet – “X” is for…


Seafaring “X” is for…

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X – The letter “X” is used by ships observing and reporting weather events to denote the development of “hoar frost”. This occurs when a white, crystalline deposit of ice is observed on solid objects, after a cold, clear night.

Hoar frost occurs when water vapour condenses (sublimates) directly to the ice phase without an intermediate liquid phase. Under clear frosty nights soft ice crystals might form on any object that has been chilled below freezing point by radiation cooling.

This deposit of hoar frost ice crystals may sometimes be so thick that it might look like snow. The interlocking ice crystals become attached to structures in nature, but also onboard ship too.

Such conditions give a typical ‘winter wonderland’ image. The fine frozen ‘feathers’, ‘needles’ and ‘spines’ can be found on any other object that is exposed to supersaturated air below freezing temperature. Hoar frost must not be confused with rime, which derives from freezing fog or glaze which forms as a continuous thick layer of ice, rather than individual frozen droplets.

The reporting of weather from ships is an important process – as surface weather observations from the ocean can make a difference to the modelling and results gained by observatories elsewhere, and indeed the data generated and calculated results which drive modern forecasts.

Most vessels report through the international scheme run by National Meteorological Services (NMSs) for taking and transmitting meteorological observations within the World Meteorological Organization (WMO) Voluntary Observing Ships’ (VOS) scheme.

The forerunner of the scheme dates back as far as 1853, when delegates of ten maritime countries came together at a conference in Brussels, on the initiative of Matthew F. Maury, then director of the United States Navy Hydrographic Office.

The US called the meeting to discuss a proposal for the establishment of a uniform system for the collection of meteorological and oceanographic data from the oceans and the use of these data for the benefit of shipping in return. As might be expected, real-time reports from the VOS are heavily concentrated along the major shipping routes, primarily in the North Atlantic and North Pacific Oceans.

The 1853 conference adopted a standard form of ship’s log and a set of standard instructions for the necessary observations. From the very beginning, ships’ meteorological observations were recognized as being essential for the provision of safety related meteorological services for ships at sea, as well as for climatological purposes.

Even today, the contribution which VOS meteorological reports make to operational meteorology, to marine meteorological services and to global climate studies is unique and irreplaceable.

One of the major continuing problems facing meteorology is the scarcity of data from vast areas of the world’s oceans (the so-called ‘data sparse areas’). Ships play a hugely important part in filling the data gaps.

The VOS fleet reached its zenith in 1984/85 when about 7700 ships worldwide were on the WMO VOS Fleet List. Since then there has been a marked decline and now only around 2500 vessels are listed on the VOS Annual ranking list. It is a shame that the number of vessels is falling – it is an excellent skill and discipline for ship’s officers, the practice of connecting with the environment and playing an important professional role in reporting is something which all ships should be encouraged to do.

X-Band Radar

X-band radar

X-Band Radar – Marine radars are key pieces of navigational and safety equipment. They provide bearing and distance of ships, land targets and objects in the vicinity from their own ship (radar scanner) for collision avoidance and navigation at sea.

Radar is a vital component of the Bridge equipment, and allows the navigator to “see” what is around the vessel. From close quarters, to significant distances away. Though anything over 24 mile range is probably subject to change and different interpretation as it gets closer.

These marine radars are X-band or S-band – which relates to the radio wave pulses they transmit and receive. The X-band is a segment of the microwave radio region of the electromagnetic spectrum. X-band is used in radar applications including continuous-wave, pulsed, single-polarization, dual-polarization, synthetic aperture radar, and phased arrays. The frequency range of the X-band is rather indefinitely set at approximately 7.0 to 11.2 GHz.

X-band radar frequency sub-bands are used in civil, military, and government institutions for weather monitoring, air traffic control, maritime vessel traffic control, defence tracking, and vehicle speed detection for law enforcement. They are also required to be carried on vessels.

As required by Regulation 19 of SOLAS V, a ship’s array comprising radar and associated equipment must include a 9 GHz (X-band) Radar. This is required on any vessel of 300 GT. and over. The significance and requirement is because X-band and radars can locate radar transponders including search and rescue transponders (SARTS).

X band is popular in modern radars as the shorter wavelengths of the X-band allow for higher resolution imagery from high-resolution imaging radars for target identification and discrimination. So the majority of marine radars operate on X-band, as it provides higher spatial resolution, better range resolution 3-6 meter and even makes small target detection easier.

It is not just on commercial ships in which X-band radar has proven attractive. A large X-band array makes up a vital part of the United States’ Federal Ballistic Missile Defense System. The SBX-1 – Sea-Based X-band Radar – is an offshore radar which operates at the high seas.

Unlike the conventional ship radars, the X-band radar is a movable, self-propelled radar system, specifically built in order to successfully pinpoint, avert and stop any attacks or threats coming towards the country. The radar was specifically built by Boeing according to the specifications required for missile defence System and is placed atop a Norwegian semi-submersible.



X-Ray – X-radiation (composed of X-rays) is a form of electromagnetic radiation, which due to its penetrating ability is widely used to image the inside of objects, obviously commonly in medical radiography, but in ports and cargo security situations too.

Most X-rays have a wavelengths are shorter than those of UV rays and typically longer than those of gamma rays. The term X-ray is usually used to refer to a radiographic image produced using this method, in addition to the method itself. Such X-ray inspection systems are becoming increasingly common, indeed a standard feature in many ports.

This rapid adoption has been accelerated by the needs of port security, and demands of legislation including the International Ship and Port Facility Security (ISPS) Code. The ability of X-rays to non-destructively penetrate entire containers and generate images of the contents in just a few seconds has been critical in balancing the demands of efficiency with security.

The systems used at most major ports deliver images which are comparable to those obtained through traditional baggage scanning at airports and capable of identifying objects smaller than a baseball.

This capability means X-ray cargo inspection is typically performed for three different objectives:

• Manifest verification – performed for tariff enforcement with the objective to confirm the contents of a container, both in type and quality. Here, operators will examine the container for overall compliance with their requirements, with less focus on small anomalies.

• Security – Perhaps most urgent need for screening cargo containers comes from the threat of smuggled special nuclear materials. The low instance, high impact occurrence means the risk of material to be used for terrorist purposes is a real threat, and one which is taken seriously. Fortunately, the densities of special nuclear materials make them clearly visible on X-ray images in contrast to virtually all permissible products. Additionally, the advent of dual-energy screening systems adds a second level of material discrimination, allowing software to clearly identify the unusual nature of this threat.

• Contraband interdiction – Image inspection for detecting contraband involves a more detailed analysis assuming that the contraband is likely to represent a small percentage of the overall container volume. In addition, perpetrators are expected to intentionally disguise or hide the materials of interest. As some contraband can be disassembled into component parts and distributed among permissible cargo, a combination of operator training and advanced software features provides a robust capability to help identify such violations.

When deciding what system to use, it is important to know what the real Inspection objectives are – as these play an important consideration in the design and implementation of the cargo screening system. What the system is to be used obviously impacts the type and utilisation of screening equipment and the process of interpreting the resulting images. Screening equipment is often specified or operated differently, depending on the screening objectives.

At the equipment selection stage, authorities consider whether mobile, “re-locatable”, or fixed installations will offer the best implementation for their needs. Fixed installations are permanent sites that are built for a specific screening system. Typically these are shielded concrete buildings where containers enter at one end and leave through an opposite exit. This allows their throughput to be limited only by the amount of time it takes to move a container through the installation.

Mobile (usually truck based) systems offer the advantage of being quickly deployable to different ports or locations but generally operate with a lower total throughput than fixed sites. A screening truck must first extend its detector boom, and then drive past one or more aligned subject containers. However, pre-staging the containers can improve the overall scanning rate.

Finally, the emergence of re-locatable scanning systems has provided a third choice, as this option takes advantage of a fixed infrastructure (control room, x-ray bay, etc.) but is designed to be readily moved to alternate sites based on user needs. Once installed, a re-locatable system operates very much like a fixed site, but with more flexibility.



XTE – “XTE” is the recognised and accepted abbreviation for the navigation term “Cross track error”. Cross track error is the distance a vessel is to one side of the straight line between two waypoints.

As vessels move between waypoints they attempt to do so in a straight (rhumb) line, or following set courses in the case of great circles. When pushed off that route, XTE is a measure of how far your vessel has moved left or right of the course.

Using GPS, there is a temptation for the navigator to simply generate a new track to the next waypoint, thus eliminating the error. While this is pragmatic, it does not address the reason for having been pushed, essentially, off course.

It is important to keep abreast of XTE information, to ensure the vessel does not wander over a navigational hazard or into an undesirable situation. The correct way to deal with XTE is to get back on the original course, then add a heading correction to keep your vessel on track. The correction angle will be proportional to the rate of drift off course.

Even with the advent of electronic navigation, the use of ECDIS does not mean that such real world effects on a vessel can be ignored. Just as has happened in shipping before, new technology brings along its own new risks. Radar and VHF “assisted collisions” are issues which were wrestled with as navigators got to grips with using these tools effectively.

With ECDIS, perhaps the biggest danger is of using technology that is not set up incorrectly. Relatively recently a high profile accident was probed by the UK Marine Accident Investigation Branch (MAIB). This led to the grounding of a large passenger ferry.

The investigators discovered that audible ECDIS alarms had been switched off and visual alarms had been ignored. The ferry grounded on a charted granite at a speed of around 18 knots. Although there were no injuries or pollution, there was extensive damage to the vessel as the hull was sliced open.

In the report, the MAIB said that insufficient passage planning had resulted in the bridge team being unaware of the limited extent of safe water available. It said that the ferry’s ECDIS was not used effectively because key safety features had been incorrectly initiated.

The MAIB found that the ECDIS safety contour value was inappropriate for the passage and approach, the visual XTE alarm had been ignored and the shallow water audible alarm had been disabled.

On the date of the accident, the crew did not take into consideration an extremely low tide and the strong tidal stream during the voyage. Thus the vessel was being pushed across the charted track – but with no alarms and visual warnings, it seems to have gone unnoticed – until the grounding. So XTE is a very important indicator of navigational performance.



Xiamen – The Chinese Port of Xiamen is an important deep water port located on Xiamen Island, the adjacent mainland coast, and along the estuary of the Jiulongjiang River in southern Fujian, China. The port comprises twelve areas including Heping, Dongdu, Haitian, Shihushan, Gaoqi, and Liuwudian.

It is one of the “trunk line” ports in the Asia-Pacific region. It is ranked the 9th-largest container port in China and ranks 17th in the world. It is the 4th port in China with the capacity to handle 6th-generation large container vessels, and has experienced significant growth – in keeping with other Chinese ports.

The world’s top 20 shipping companies have all established major shipping routes and operations in Xiamen. A total of 68 shipping routes serve over 50 countries to almost all the major ports in the world, yielding an average 469 ship calls at the port each month.

In addition, passenger services also operate from Xiamen to Hong Kong, Guangzhou, Shanghai and Wenzhou, as well as frequent ferry service to the Shuitou terminal in Kinmen Island (R.O.C.).

The port is owned and operated by Xiamen Port Authority which is a department of the Xiamen Municipal Government. It is also deemed a “sister” port of Port Klang in Malaysia.

The coast line in the harbour area stretches for 30 kilometres, and the depth of water reaches up to 17 metres. The port offers 74 berths, and there are nine container terminals.

Xiamen Island was considered to possess one of the world’s great natural harbours in Yundang Bay, but Fujian’s international trade was long restricted to Quanzhou or to Guangzhou in Guangdong. Due to the silting up of Quanzhou’s harbour, the British insisted that Xiamen be opened to foreign trade in the treaty that ended the First Opium War in 1842.

As part of China’s “Opening-Up Policy” under President Deng Xiaoping, Xiamen became one of the original four special economic zones opened to foreign investment and trade in the early 1980s. Its former harbour was enclosed using land excavated during the city’s expansion.

The city is known for its mild climate, and colonial architecture, as well as its relatively low pollution. As such it regularly figures in surveys on the best places to live in China, as well as providing a good quality of life, it has even been referred to as China’s “most romantic leisure city”. Which is nice.



Xtra Large – “XL” is increasingly the size of choice for seafarers when getting new boiler suits. There are growing concerns about obesity at sea, and the fact that seafarers are increasingly unhealthy, sedentary and are putting on weight.

While stating the XL is now the average size of boiler suits on most vessels, we are perhaps using some poetic licence – but there is a real problem, and it is only getting bigger. Literally.

The problem of increasing weight is so serious that in the offshore sector new rules have been introduced for ‘larger’ oil workers travelling to and from offshore installations by helicopter. There has already been changes to cruise ship lifeboat safety to take into account increasing passenger sizes and weights.

The changes have come after a study revealed the average oil worker had risen in weight by close to 20% over the past 30 years’. While various studies have analysed the rising tide of obesity among seafarers.

All seafarers that go to sea must have a statutory medical examination every two years to prove they are in good enough health and fitness to carry out their duties. Obesity is a common cause of physical incapacity in serving seafarers.

Some of the most important conditions affecting fitness, and in turn affecting seafarer medical examinations, are heart attacks, artery disease and diabetes – conditions that can be directly linked to obesity.
Body Mass Index (BMI) is the most commonly accepted measure of general obesity, and is one of the tests included in seafarer medical examinations. Adults are classed as overweight if their BMI is between 25 and 30, obese if their BMI is 30 to 40 and morbidly obese if their BMI is 40 or more.

A study of Danish seafarers found they were statistically significant more overweight seafarers in all age groups compared to a reference group ashore. Among those between 45 and 66 years of age 76.6% had a weight above normal, while 30.9% of this age group was obese.

A similar study of Turkish seafarers found similar results. As the BMI values of Turkish seafarers were boomed over the years. As Turkish male seafarers get older, their BMI values rise progressively. According to the study, after the age of 28, BMI scores increasingly exceed the acceptable level. They continue to rise to maximum average values when the seafarers are in their 50s, a time when other health concerns can also come to the fore.

Studies of other seafarer groups have also come to similarly stark and worrying conclusions. Even amongst “healthier” races, such as from Asia – there are growing concerns over obesity too. Obesity rates in the Philippines are currently at around 30%, and once more seafarers are seen as a bellwether of such changes.

Obesity is a dangerous killer in its own right, but in a seagoing environment there are even more immediate risks. These include:

• Inability to undertake arduous emergency tasks such as fire-fighting, evacuation from the vessel and recovering people from the water. Difficulty entering and leaving restricted spaces, during normal duties and especially if needing rescue because of collapse or injury
• Increased risk of injury from falls and of acute illness and incapacity while at sea
• Inability to fit into protective clothing and lifesaving equipment.
• Exceeding the design standards for equipment used to work at heights and for use in life threatening situations, for instance emergency chutes and free fall lifeboats.

The problems and limitations posed by obesity create risk both for the seafarer themselves and for other crew members, this is an issue which needs to be urgently tackled.



Xmas – Christmas is a special time of year. A time of celebration and coming together. Obviously that can make it difficult being away from home, especially out at sea.

Actually it makes no difference whether it is Christmas or Diwali, Ramadan or Thanksgiving, there will be celebrations, special times and things going on back at home that seafarers will feel disconnected from.

Sadly being away at such times can really magnify the sense of isolation and disconnect. There can be feelings of sadness, resentment, perhaps even anger. These can have a bad effect at sea, and so it is important to consider what can be done to lesser the effect.

Keeping a brave face is one way of coping – but really, that stiff upper lip isn’t going to lessen the effect inside. So just how do people at sea cope and stay relatively happy away from family, when the rest of the world is partying, celebrating or spending holy times of reflection?

How Christmas is played out onboard ship depends on many different factors, and of course since alcohol is no longer much of a consideration, then the festivities can be a little flat. If the vessel is alongside and not working, then with most people on day work, there can be some relaxation.

The catering crew really take on a whole new level of responsibility when it comes to high days and holidays. A crew which is able to eat heartily and enjoy a festive feast will still miss home, but the pain will be eased.

For those on ships at sea, well it can be something akin to a normal working day. Which can in some ways be a blessing in disguise. Not having to pretend to do “festive” things can get the day out of the way, and seafarers can just look forward to getting home.