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


Seafaring “Z” is for…

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Z-Drive – A Z-drive is a type of marine propulsion unit and is in essence an azimuth thruster. The pod can rotate 360 degrees allowing for rapid changes in thrust direction and thus vessel direction.

Z-Drive configurations are designed to independently rotate 360 degrees. The use of an electric drive removes the need for long propeller shafts, and the rotatable pods offer the advantage of applying thrust at any angle through the entire 360 degree field of motion, thus increasing the ship’s manoeuvrability.

Podded drive systems have been installed on several classes of large commercial vessels. They are very popular on cruise ships due to the manoeuvring capabilities and the benefits of the diesel electric setup. This allows the designers greater freedom, as they can place main engine anywhere in the vessel and run power easily to the electric propulsion motor in the unit.

There are a number of advantages, as Z-drive modular propulsion units are advantageous where there are draft issues and they also simplify construction and maintenance. They are more efficient too. Some studies claim Z-drive propulsion is as much as 14% more efficient compared to conventional propulsion.

The Z-drive is so named because of the appearance (in cross section) of the mechanical driveshaft or transmission configuration used to connect the mechanically supplied driving energy to the Z-Drive azimuth thruster device. This form of power transmission is called a Z-drive because the rotary motion has to make two right angle turns, thus resembling the letter “Z”.

The Z-drive transmission was invented in 1950 by Joseph Becker, the founder of Schottel, and used in the first azimuth thrusters built by Schottel GmbH in Germany in the 1960s under the Schottel brand name and referred to as Rudderpropeller ever since. Joseph Becker was ultimately awarded the Elmer A. Sperry Award for this invention as a major contribution to the improvement of transportation worldwide.



Zeebrugge – The Port of Zeebrugge is a large container, bulk cargo, new vehicles and passenger ferry terminal port in the municipality of Bruges, Flanders, Belgium,

The port handles over 50 million tonnes of cargo annually, and handles over 10,000 ship moorings annually. It is also a major employer in the area. The port directly employs over 11,000 people and figures suggest that indirect employment relating to the port is around 22,000 people.

The port was inaugurated on July 23, 1907 by King Leopold II, arriving by sea. From this small start and years being considered as purely a transit port, Zeebrugge has gradually evolved into a centre for European distribution.

The port has become a major European port since major development works were carried in the 1972 to 1985 period. Since then total tonnage has doubled. It is now considered a major multifaceted port, one that handles a wide range of trades. It is particularly known for its trade of unit loads (trailers and containers), but also deals with new car shipments as well as a thriving conventional general cargo trade. It also deals in ‘high & heavy’ cargoes, as well as dry and liquid bulk cargoes and natural gas.

It is Europe’s leading RoRo port, handling 12.5 million metric tonnes in 2010, and the world’s largest port for imports and exports of new vehicles. It is also Europe’s largest terminal for liquefied natural gas (LNG), receiving natural gas from the Troll gas field via the 814 km long “Zeepipe” under the North Sea.

LNG is also delivered in specialised gas tankers from various origins, like Africa, Australia or the Middle East. Zeebrugge counts as one of the most important ports in Europe for containerised cargo as well. It also ranks as a United States, CSI (Container Security Initiative) port.

Sadly the port has become famous for a maritime tragedy, the loss of the ferry “Herald of Free Enterprise” (owned by Townsend-Thoresen). On 6 March 1987, was just outside the port when it took on water due to the bow doors remaining open, became unstable and capsized, killing 189 passengers.



Zenith – The zenith is the “highest” point on the celestial sphere (meaning it is the farthest up from the gravitational force). The zenith is the imaginary point directly “above” a particular location, on the imaginary celestial sphere.

The term zenith is sometimes used to refer to the highest point, way or level reached by a celestial body during its apparent orbit around a given point of observation. This sense of the word is often used to describe the location of the Sun (“The sun reached its zenith…”) – the point at which it then appears to drop in the sky.

The opposite of zenith is the “nadir”. This is the direction pointing directly below a particular location; that is, it is one of two vertical directions at a specified location. Since the concept of being below is itself somewhat vague, scientists define the nadir in more rigorous terms. Specifically, in astronomy, geophysics and related sciences (e.g., meteorology), the nadir at a given point is the local vertical direction pointing in the direction of the force of gravity at that location.

Nadir also refers to the downward-facing viewing geometry of an orbiting satellite, such as is employed during remote sensing of the atmosphere, as well as when an astronaut faces the Earth while performing a spacewalk.

Both terms zenith and nadir can also be used to represent the highest or lowest point reached by a celestial body during its apparent orbit around a given point of observation.

Zheng He – Dubbed the “Chinese treasure fleet” over 600 years ago the great Ming armada weighed anchor in Nanjing, on the first of seven epic voyages as far west as Africa—almost a century before Christopher Columbus’s arrival in the Americas and Vasco da Gama’s in India.
Even then the European expeditions paled by comparison. The ships of Columbus and da Gama combined could have been stored on a single deck of a single vessel in the fleet that set sail under Admiral Zheng He.

Zheng He was a visionary who imagined a new world and set out consciously to fashion it. It seems more likely that the world and all its continents were discovered by Zheng He, and not Columbus et al.

His fleets roamed the oceans between 1405 and 1435 and his exploits, which are well documented in Chinese historical records, were written about in a book which appeared in China around 1418 called “The Marvellous Visions of the Star Raft”.

His missions were astonishing as much for their distance as for their size: during the first ones, Zheng He travelled all the way from China to Southeast Asia and then on to India, all the way to major trading sites on India’s southwest coast. In his fourth voyage, he travelled to the Persian Gulf. But for the three last voyages, Zheng went even further, all the way to the east coast of Africa.

The first expedition of this mighty armada (1405-07) was composed of 317 ships, including perhaps as many as sixty huge Treasure Ships, and nearly 28,000 men. In addition to thousands of sailors, builders and repairmen for the trip, there were soldiers, diplomatic specialists, medical personnel, astronomers, and scholars of foreign ways, especially Islam.

Some of the ships were said to have been 137 meters (450 feet) long and 55 meters (180 feet) wide, which was at least twice as long as the largest European ships of that time. Some sources claim the ships were even longer — 180 meters (600 feet). Though there are disputes as to whether wooden vessels of that size would be feasible.

Around these times China had been extending its power out to sea for 300 years. To satisfy growing Chinese demand for special spices, medicinal herbs, and raw materials, Chinese merchants cooperated with Moslem and Indian traders to develop a rich network of trade that reached beyond island southeast Asia to the fringes of the Indian Ocean.

By the beginning of the Ming Dynasty, China had reached a peak of naval technology unsurpassed in the world. While using many technologies of Chinese invention, Chinese shipbuilders also combined technologies they borrowed and adapted from seafarers of the South China seas and the Indian Ocean. For centuries, China was the preeminent maritime power in the region, with advances in navigation, naval architecture, and propulsion.

From the ninth century on, the Chinese had taken their magnetic compasses aboard ships to use for navigating (two centuries before Europe). In addition to compasses, Chinese could navigate by the stars when skies were clear, using printed manuals with star charts and compass bearings that had been available since the thirteenth century. Star charts had been produced from at least the eleventh century, reflecting China’s concern with heavenly events (unmatched until the Renaissance in Europe).



Zodiac – The zodiac is the circle of twelve 30° divisions of celestial longitude employed by western astrology and (formerly) astronomy.

The western zodiac is centered upon the “ecliptic”, the apparent path of the Sun across the celestial sphere over the course of the year. The paths of the Moon and visible planets also remain close to the ecliptic, within the belt of the zodiac, which extends 8-9° north or south of the ecliptic, as measured in celestial latitude.

Because the divisions are regular, they do not correspond exactly to the boundaries of the twelve constellations after which they are named. Historically, these twelve divisions are called signs. Essentially, the zodiac is a celestial coordinate system, or more specifically an ecliptic coordinate system, which takes the ecliptic as the origin of latitude, and the position of the Sun at vernal equinox as the origin of longitude.

In navigation, the zodiac also refers to the “celestial sphere” is an imaginary sphere of arbitrarily large radius, concentric with Earth. All objects in the observer’s sky can be thought of as projected upon the inside surface of the celestial sphere, as if it were the underside of a dome or a hemispherical screen. The celestial sphere is a practical tool for spherical astronomy, allowing observers to plot positions of objects in the sky when their distances are unknown or unimportant.



Zulu – “Zulu” time is that which you might know as “GMT” (Greenwich Mean Time) or time at the Zero Meridian. Navies the world over as well as the Merchant Navy and civil aviation, use the letter “Z” (phonetically “Zulu”) to refer to the time at the prime meridian.

When the concept of time zones was introduced, the “starting” point for calculating the different time zones was agreed, and so Greenwich Mean Time (GMT) is the mean solar time at the Royal Observatory in Greenwich, London.

Most time zones were based upon GMT, as an offset of a number of hours (and possibly a half-hour) “ahead of GMT” or “behind GMT”.

Unfortunately the Earth does not rotate at exactly a constant rate. Due to various scientific reasons and increased accuracy in measuring the earth’s rotation, a new timescale, called Universal Time Coordinated or Coordinated Universal Time (UTC), has been adopted and replaces the term GMT.

Though legally, the civil time used in Britain is called still “Greenwich mean time” (without capitalisation), according to the Interpretation Act 1978, with an exception made for those periods when the Summer Time Act 1972 orders an hour’s shift for daylight saving.

Thus the law provides that whenever an expression of time occurs in an Act or parliament, the time referred to shall (unless otherwise specifically stated) be held to be Greenwich mean time.

Zumwalt – The Zumwalt-class destroyer is a class of United States Navy guided missile destroyers designed as multi-mission stealth ships with a focus on land attack.

The class is multi-role and designed for surface warfare, anti-aircraft warfare, and naval gunfire support. They take the place of battleships and are designed to require a smaller crew and be less expensive to operate than comparable warships.
The lead ship is named USS Zumwalt for Admiral Elmo Zumwalt, and carries the hull number DDG-1000.

It has a wave-piercing “tumblehome” hull form whose sides slope inward above the waterline, which has been stated to reduce the radar cross-section (RCS) by returning much less energy than a conventional flare hull form. The vessels’ appearance has even been compared to that of the historic ironclad warships such as the Monitor.

Despite being 40% larger than an Arleigh Burke-class destroyer, the radar cross-section is more akin to that of a fishing boat, according to a spokesman for Naval Sea Systems Command. The tumblehome hull and composite deckhouse reduces radar return. Overall, the destroyer’s angular build makes it “50 times harder to spot on radar than an ordinary destroyer.

Originally 32 ships were planned, with $9.6 billion research and development costs spread across the class. As costs overran estimates, the quantity was reduced to 24, then to 7, and finally to 3, significantly increasing the cost-per-ship to $3.96 billion (excluding R&D costs) – well-exceeding the per-unit cost of a nuclear-powered Virginia-class submarine ($2.688 billion).

Lawmakers and others have questioned whether the Zumwalt-class costs too much and whether it provides the capabilities the U.S. military needs. There have been concerns about reliability too – recently USS Zumwalt, suffered an engineering problem in the Panama Canal and had to be towed to port.