15,000 dwt to the first 50,000 dwt in 1956 to the 200,000 dwt Idemitsu Maru in 1962, culminating in the 550,000 dwt giants of 1976 like Shell’s Batillus. Nearly all such vessels were built in building docks, some spanned by gantry cranes of up to 1000 tonnes capacity. An enabling technology was computer aided design, initially used to mechanise tedious naval architectural hand calculations from the late 1950s, but soon applied to structural analysis where finite element methods allowed ever larger tankers to be designed with greater confidence. In due course CAD was linked with computer aided production with full product models associated with numerically controlled machine tools. The fourfold increase in oil prices in 1974 not only halted


the growth of tankers but encouraged the search for offshore oil. While jack-ups were adequate in shallower waters, drilling in deeper waters required semi-submersibles. Motion analysis programs were essential, and coupled with dynamic positioning using thrusters, increased operability in all manner of offshore vessels. The bulk carrier concept of a single-deck vessel with


hoppered holds was not new, as it had been used in short sea colliers for decades. But it was not applied to deep sea ships until the late 1950s, although iron ore carriers with their small central cargo holds dated from the 1920s. Size grew steadily from the initial 20,000 dwt to over 100,000 dwt by 1968. The late 1950s and 1960s saw a great increase in specialist ship types, as demand for large volumes of cargoes like export motor cars justified a tailor-made design rather than a general purpose ship. Liquefied Petroleum Gas (LPG) carriers were another 1950s


development, where cargoes like propane could be liquefied either by cooling to about -48o


C, or in smaller tanks by


pressure alone. A more demanding technology was required for Liquefied Natural Gas (LNG) which liquefies at -1631o


C,


so requiring heavily insulated tanks separate from the main hull structure. The first purpose built LNG ship was Methane Progress of 27,400 m3


LNG carriers have now broken the 200,000 m3


in 1964 with aluminium alloy tanks. barrier.


The impetus for specialist ships comes when volume of


a particular trade expands to a level sufficient to support a dedicated fleet. The increased efficiency and improved quality of cargo outturn can outweigh the lack of flexibility for alternative cargoes. It was the inefficiencies of the multi-deck general cargo ship that spurred the development of the container ship to reduce port time from a week or more to a day or so. Standardisation of container dimensions by ISO in 1965 paved the way for its widespread adoption. The now ubiquitous 20ft and 40ft boxes allowed mechanised handling and stowage processes and equipment to be developed. Such was the increase in productivity from larger faster container ships that one vessel replaced five or six break-bulk vessels, so all the main trade routes had been containerised by the mid-1970s. Since then the 3000 TEU (20ft equivalent unit) ship has grown to 14,000 TEU, although speeds have remained in the mid-20s knots. The short sea roll-on/roll-off vessel offered big reductions in port time where trailers could be


44


used, as well as providing a drive-on/drive off facility for cars and trucks. It was in the 1950s that the use of turbocharging in


2-stroke diesels and cheap heavy fuel oil enabled the slow speed direct drive engine to challenge the steam turbine in bigger ships. That remains the prime mover of choice today, although the emphasis is now on reducing emissions which require higher quality fuel. Geared medium-speed diesels had been developed between the wars, and postwar were favoured in smaller vessels and in low headroom ships like ferries. Post WWII deep sea passenger vessels continued to be


built in significant numbers. But long distance passenger sea transport had been overtaken by air transport by the late 1950s, so by the late 1960s all the large liners had been scrapped or converted to cruising. But as that door closed, another opened, the purpose built cruise ship. Ever larger and more luxurious floating leisure centres developed into today’s 150,000 gt plus monsters carrying 4000 plus passengers. Transport of passengers is today focussed on short sea ferries, including vehicle transport. From the 1960s, high-speed craft began to challenge conventional ferries on short routes, with speeds of 35-50kts. With their inherently low lift/drag ratio, light alloys were needed to keep hull weight down and gas turbines often used to provide the high power, while waterjets were developed to ever higher powers. While fibre-reinforced plastic has been used in some high-speed craft, a much larger market has been in mass produced leisure craft. Gas turbines have been the prime mover of choice for most


high-speed warships from the late 1960s, derived from aircraſt jet engines. High power-weight ratio and reduced manning have for military vessels outweighed the disadvantage of high fuel cost. Electric propulsion technology with high power density motors has increased the number of ships with full electric propulsion, especially those with a wide range of power demands, whether naval, commercial or offshore. Azimuthing thrusters have become the propulsor of choice for tugs, giving greater manoeuvrability as well as a smaller crew. But perhaps the most pervasive recent influence has been the


ever increasing technical regulatory demands and standards. Coordinated by IMO, the intent is to achieve international agreement before implementation by individual flag states. But the marine industries have for historical reasons had more fragmented regulatory regimes than land based industries, so adoption of readily applicable best practice takes time. So perhaps what the marine industries need in the next decades is to focus enabling technologies on getting the best out of well established concepts like steel hulls and internal combustion engines by improving reliability, operational efficiency and mitigating the safety and environmental impacts of ships, but without jeopardising the technical and economic gains of the last 150 years. The professional institutions have a continuing role in discussing and disseminating the best ways forward, largely using the English language, now universally adopted in the maritime industries.


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