Designing marine vessels and structures that will stay afloat, survive the harsh weather thrown at them, and are cost effective to build and run is specialist skill. The art and science of creating those designs for commercial, military and recreational use, is practised by a professional engineer known as a Naval Architect. These highly trained experts are responsible for the design, construction and repair of ships, boats, other marine vessels and offshore structures, both civil and military. All marine vessels and structures must be constructed to exacting designs that take into account strength and stability. In the case of ships, speed, trim and weight must also be taken into account. Without such considerations, these vessels and structures simply would not float. For ships, the Naval Architect works out the vessel in detail in construction drawings (or sheet plan or working plan) and floor plans. These designs must accurately tie together the structural considerations of the vessel, all the while keeping in mind the function, appearance, safety and costs. In the case of ship construction, certain essential drawings have to be submitted to the classification society where the ship is to be registered before construction and the whole of the design has to live up to the legal demands of the classification society. A Naval Architect can also be responsible for the maintenance of vessels in service, repair of sea-going vessels and offshore constructions, such as oil rigs, and for valuation proceedings. Some naval architects are employed as surveyors, ensuring that vessels and structures comply with safety regulations. They might also be called upon to give professional advice and technical support to customers of the maritime industry. Naval Architects will often liaise with other marine specialists such as naval professionals, marine engineers, scientists, business managers, lawyers and accountants to ensure that they produce designs which meet the requirements of clients and are safe, seaworthy and economic.