Ship Draughtsman Continued

Although wartime production of mild steel had included armour plating and special alloy steels for armaments, shipbuilding continued to use a general-purpose steel having a tensile strength of between 26 and 32 tons per square inch.’⁵ The draughtsman’s calculations for non-standard structures were based upon this, and other requirements could be safely taken from Lloyds Rules for the Construction and Classification of Steel Ships. As far as high carbon steels were concerned, Walton noted in 1944 that ‘very little is definitely known of their higher elastic limits or yield points’,’⁶ so that in areas of particular stress, for example, in the corners of hatch openings, stresses were catered for by simply increasing the thickness of plate, and champhering the edges to match up with adjacent plates.

In 1959 the major classification societies standardized their requirements for steel, for, with the increase in the size of ships and correspondingly higher structural stresses, it proved impractical merely to increase the thickness of plating or stiffeners. The result was that differing grades of steel were developed for merchant shipping. The use of these steels was a natural development of those used in warship building, and draughtsmen would have been able to familiarize themselves with their capabilities, including the welding techniques necessary for high grade steels, in a paper on their use published by the NECIES.’⁷ They also had to adapt to the new Lloyds Rules which were originally set out as a series of tables. During 1966 the Rules were rewritten, and reissued in 1967. These new Rules were formula based to cater for new ship types, and the general increase in the size of vessels.

The use of a number of grades of steel in the same hull resulted in lighter structures, but demanded a greater expertise from the draughtsman to ensure that poor structural detail did not result in unacceptable stresses being built into the Unit, and, ultimately, into the completed hull.

Although steel has been the prime material of the shipbuilding industry, aluminium alloy has also been of importance for its resistance to corrosion, and non-magnetic properties which has resulted in its adoption by builders of leisure craft and mine protection warships. The major advantage for merchant shipping and the larger warships, however, is its light weight, being only around one-third the weight of mild steel.

While an assessment of aluminium alloy as a shipbuilding material had been published early in 1946J~ it was not until two years later that the NECIES published the first of two papers concerning superstructures,’⁹ when the north-east draughtsmen could familiarize themselves with the capabilities of this, for them, new material.

The major contract in the region employing extensive use of aluminium alloy was that of the passenger liner MS Bergensfjord, which began building in 1954 at the Wallsend yard of Swan Hunter & .Whigham Richardson. All the superstructure above the weather deck was aluminium alloy which, although expensive when compared to steel, saved a great deal of top weight thus improving stability, speed, and passenger capacity. In a joint paper to the NLCIES in December 1956, Swan Hunter’s technical manager acknowledged this ‘opportunity to gain valuable experience in the field of light alloy construction ,20 and gave details of the argon gas welding procedures, as well as the strength characteristics of the materials employed. Although not all of the company’s draughtsmen were employed on this particular contract, the opportunity was there to assimilate the technical differences in design, detailing, and construction methods.

Since the Bergensfjord entered service in May 1956, a number of yards have used aluminium alloy, primarily for superstructures, and the drawing offices have adapted to the techniques and regulations subsequently formulated by the regulatory bodies. It was another instance where progress in one field, ie. metallurgical development of heat treated aluminium alloys, resulted in design changes in another industry.

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