Trans RINA, Vol 152, Part A2, Intl J Maritime Eng, Apr-Jun 2010
shows one of the tankers so tested. By the 1960s, the transition from riveting was complete. Lighter smoother hulls paved the way for ever larger ships.
Welding came of age in the 1930s. Introduced in the 1900s using gas, the shielded electric arc was developed in time for WW1, where it proved useful in awkward repairs. The
first all-welded seagoing ship was the
coaster Fullagar built by Cammell Laird in 1920 (at a loss!). But welding was regarded as expensive, unproven and less reliable than riveting, especially for main hull structures. So it tended to be used where there were clear advantages such as oil tight bulkheads in tankers or oil fuel bunkers, where really oil tight riveting was difficult to achieve. It took the high production demands of WW2 to bring about the widespread use of welding. The huge emergency shipyards in the USA were laid out for all welded prefabricated construction, with large welding bays, heavier cranage and ample storage space for units – and needing less skilled labour. Without welding, the US would not have been able to build the 5000 ships that the Maritime Commission produced between 1941 and 1945. But there were still problems to be solved with brittle fracture, requiring the development of notch tough steels in the late 1940s, and the need to integrate design and construction more closely, both in terms of detail design to remove stress concentrations and in block assembly methods. But welding brought significant performance advantages in terms of lower structural weight (typically about 15% by removing overlapped riveted
flanges and connecting angles) and in smoother hulls, typically about 20% less resistance. Ramsay Gebbie of Doxford made a careful comparison of an all-riveted and an all-welded cargo ship of equal cargo deadweight (9515 tons) and speed (14 knots) in his 1958 Amos Ayre INA lecture. He concluded that owing to the lighter, smaller and smoother hull, power and fuel consumption were reduced by about 20%, and building cost by about 12%, while the profitability of the riveted ship was at best 90% of the welded ship, and could be as low as 52% depending on freight rate, fuel price and port time. By 1960 the transition was complete.
3. POST WORLD WAR TWO
The last half of the 20th century saw the fastest ever evolution in ship development, with size increasing tenfold, more new ship
types and the container
revolutionising general cargo transport. On the naval side, the nuclear propelled submarine changed warfare for ever, recovery
both strategically and tactically. Postwar saw a booming world economy, with oil
replacing coal as the primary energy source. Tankers increased dramatically from the ‘three twelves’ of prewar (12,000dwt at 12knots on 12tons oil per day) to the first 50,000dwt in 1956 to the 200,000dwt Idemitsu Maru in 1962 culminating in the 550,000dwt giants of 1976 like Shell’s Batillus with a draft of around 28m – although the latter class proved too large and inflexible in service, and none remained in service long. Nearly all such vessels were built in building docks, some spanned by gantry
cranes joints, of up to 1000tonnes lifting capacity,
enabling very large blocks and complete superstructures to be lifted. Ports expanded continually to accept such large vessels, with a corresponding demand for dredgers, usually suction, capable of as much as 30m (100ft) depth.
A particular enabling technology was computer aided design (CAD), 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 methods 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, resulted in increased operability in all manner of offshore vessels. Many of these vessels had helicopter landing decks, as did most major warships from the 1960s.
Figure 10. The submarine enabled smaller navies to strike at larger
navies using the torpedo. Airless underwater propulsion (electric motors and batteries for
The bulk carrier concept of a single deck vessel with hoppered holds was not new, as it had been used in short sea gas and electricity colliers for decades. But it was not applied to deep sea ships until the late 1950s, although deep sea iron ore carriers with their small central cargo holds dated from the 1920s. The bulk carrier design was ideal for grain and ore cargoes, which hitherto had been mostly carried in tween-deck cargo vessels. Size grew
the first half century), safe submergence and surfacing, and control
in three dimensions were demanding
technologies. Medium speed diesels were the prime mover of choice for surface propulsion and battery charging until nuclear power arrived in the 1960s. The shape of the British Uther of 1943 shows to advantage in drydock, with the prominent ballast tanks.
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©2010: The Royal Institution of Naval Architects
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