Ship Draughtsman Continued

TECHNICAL CHANGES During The War Years

The technical changes to which the ship draughtsman has adapted since 1945 can be Listed under four main headings. These are welding and prefabrication; materials; new ship types; and the advent of computers. Although these changes took place at various times, and over varying periods of time, they can be readily identified by a comparison of two standard textbooks used in the industry: Steel Ships published in 1944 and reissued in 195O, and Ship Construction published in 1994.

If one development can be said to have pointed the way forward for postwar shipbuilding, it must be the wartime Liberty Ship programme which began in 1940. Developed by the California Shipbuilding Corporation, to an original design by J.L. Thompson & Company on the River Wear, this shipyard launched 11 ships, and delivered another 15, in just one month in 1942, and demonstrated the advantages to be gained by the use of electric arc welding and prefabrication.

The old riveted construction was essentially a piece-by-piece assembly where nearly every component was fitted to the next on the building berth to ensure accurate lining up of the ship’s structure. Welding allowed components to be fitted together in sub-assemblies on a flat surface, where down-hand welding could be employed, thus making for easier, and cheaper, construction. It also allowed girders and stiffeners to be used in a manner which produced stronger and lighter construction. Whereas riveted angle bar stiffeners were fixed by the flat part of the angle (thus: L ), welded stiffeners were reversed and welded by the ‘toe’( -is),so that most of the metal of the stiffener was away from the plate to be stiffened. This results in a much stronger structure, so that a smaller size of angle bar can be fitted, thus saving weight and cost. Each sub-assembly could be turned around to facilitate easier welding and attachment to other sub-assemblies. The disadvantage with the new technique is that welding causes shrinkage and some distortion of the metal, unlike the fastening of riveted joints, and that allowance for distortion had to be made in the design, planning, and material cutting stages.

Readjustment to these new techniques was referred to by A.J. Marr in a paper to the Student Section of the North East Coast Institution of Engineers & Shipbuilders (NECIBS), when he noted that before the start of welding and prefabrication ‘there was not much that the drawing office had to know about the yard facilities’, but now the draughtsman’s knowledge ‘must be related to the requirements of erection’.⁶

Despite the availability of data on welding and prefabrication, the Tyne and Wear yards were said to be ‘run down’ and operating, in 1945, very much as they had done decades earlier.⁷ The exception was Bartram’s yard on the Wear, who had, with government assistance, re-equipped with overhead electric cranes allowing them to use prefabrication techniques and large-scale welding of up to 85%.⁸ Bartram’s Weekly Returns on Employment of Trades records that from about equal numbers at the end of the war, by 1957 there were six welders for every riveter. The total riveting and welding force increased by 67 per cent, but the percentage of riveters fell from 50 per cent to only 14 per cent.⁹

The move towards all welded prefabricated ships was not reflected in all the region’s yards, for Pickersgill built their last all-riveted ship, the Needles, as late as 1958.10 This apparently tardy adoption of large-scale welding is also reflected in a shipbuilding text book published in 1950, but which still retains the 1944 edition’s regard for welding as 'in a more or less experimental stage'."

The strength and reliability of welding was a matter for concern to draughtsman, builder, owner, and classification societies alike. They were expressed in a number of articles such as the alarmingly titled ‘The Breaking in Two of Welded Ships’,’² which considered the disposition of welded joints, and the stresses imposed by the process itself, and the alignment of prefabricated units. The dangers of water traps and subsequent corrosion were also dealt with in other articles,’³ although these latter problems were common to both riveted and welded construction.

Much was done by the shipping press to bring these practical problems to the attention of the ship structural draughtsmen. Unlike riveted joints which could cater for a number of components joined at a common point such as occurred at the edge of shell plates, early welding design called for joints to be staggered so that the intersection of welds did not undercut the steel or cause brittle fractures, the so-called ‘hot spots’. This was the subject of the first of a series of articles in the Shipbuilding and Shipping Record,’⁴ which enabled draughtsmen, who were perhaps not at a yard where welding and prefabrication were fully adopted, to gain extensive knowledge of the emerging techniques.

By the late 1970s structural plans had ceased to be drawn showing the whole of a main structural element, for example, the Upper Deck Plan or all the Watertight Bulkheads. These plans were now drawn for an entire prefabricated Unit, and showed only the relevant sections of decks and bulkheads as required by the planning and construction departments, and the draughtsman now also worked to the datum lines needed for laser sight alignment, as well as the old method of frame numbers. Ships were now designated in Units (or construction blocks), and within them, zones. Most items such as pipes, vents, seatings, and bought-in equipment which had to go into each zone were attached to the Units before erection on the building berth. This technique of ‘pre-outfitting’ increased the work of the drawing offices, the planning, production, and purchasing departments in terms of parts lists and building schedules, and many draughtsmen found themselves transferred to these expanding departments, and no longer required to produce drawings.

Continue on with Material Improvements