Materials & Fabrications requirements for current
and future vessels.
Paper Title: “Materials and Fabrications requirements for current and future vessels “presented by Norrie McPherson, DSC, from BAE Systems.
Norrie outlined the structure of BAE systems, the various “yards “of which it was comprised and each of their specialisations. He then gave a brief review of the design of some naval vessels, historic and those of the future, commenting on their features, the materials of their construction and the thicknesses used.
He then went on to tell us of the types of vessels recently completed by BAE Systems Surface Ships the Type 45 destroyers, the most advanced warships in the world, patrol boats and those currently under construction the Queen Elizabeth Class Aircraft Carriers. (QEC)
Norrie explained that the biggest material challenge was thin plate distortion this arises because there is so much welding in the construction of modern vessels. Where you have heat input you have distortion. A way of trying to reduce distortion is to reduce the amount and size of welds, the use of temporary ribbing bars. Consider the “design “input into distortion and to make use of modelling techniques. From this, different techniques and process are used for different thicknesses, material specification reviewed; egg use of higher strength steels, and laser cut thin plate and various other techniques. By doing this the amount of rework due to distortion has been reduce by 80%. This was achieved by the combined efforts of a number of parties.
A problem that has been encountered is the inability in certain areas is the lack of understanding of people that if you really drive prices down for materials and components then quality will suffer, with inferior items being supplied without the customer being advised of the change in specification, resulting in problems.
The QEC Aircraft Carriers are being built in sections at various locations around the country brought to Roysth where they will be put together. Bae systems at Govan will be building at least 2 blocks for each carrier. To endeavour to minimise distortion and problems due to welding use is being made of Finite element modelling, this allows possible design and material changes to be considered. Wherever possible the use of modular construction techniques, long used on Clydeside, is being used. The challenges are many and great, from bulkheads 50mm thick , the flight deck 36mm with over 4,500 link plates to be welded into the flight deck and hanger deck, lighting units and fire fighting nozzles to be welded in as well.
The A frames , which carry the shaft are too large to be cast as one will require to be welded, though this will be carried out by the foundry. Shaft alignment is critical in such ships. A lot of work has been and continues to be done on the welding processes, techniques, consumables, including gases, procedures and sequences by BAE Systems, Govan, together with their Suppliers and a number of Universities to minimise or eliminate problems. Material specification is constantly under review sometimes trading one property of against a better outcome.
The buffet was sponsored by the Scottish Branch of the IBF