Design of an underwater towfish using design by rule and design by analysis

Abstract

The European unfired pressure vessel code EN13445-3 [1] has been used to design a preliminary prototype of a towfish. The towfish is essentially an underwater vessel equipped with various sensors, cameras, hydroplanes and control systems that are used to capture data on the levels of pollutants in the sea and at the same time monitor plankton and jellyfish levels. The towfish is towed behind a surface ship and is designed to dive to a depth of 50m below sea level. The depth of dive can be controlled by means of hydroplanes. Data, signals and electrical power are transferred from the towfish to the surface ship and vice versa via the towing line. From a structural point of view the towfish is a vessel acted upon by external pressure and local loads. Design by rule (DBR) was first used to calculate some of the various dimensions and thicknesses of the towfish components. The various components were designed mainly to prevent failure due to buckling. Design by analysis (DBA) based on Annex B of the pressure vessel code EN13445-3 [1] was then used to carry out further buckling checks that were not possible to do using design by rule. At the end of the paper the results from the two design approaches are compared and any major differences are highlighted.