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A lot of research has been conducted on welding techniques and appropriate materials to reduce manufacturing time and costs without compromising on desired mechanical properties in shipbuilding. One of them is about reducing dimensional shrinkage after welding process. Shipbuilders achieve this phenomenon by applying overall redundancy of the mismatch between the design and dimension of plates which is formed due to the welding shrinkage during joining of two parts. This situation adds significantly to the material cost when the entire ship is considered. Therefore, it is important to study the stability of welding parameters to achieve a high-quality welding. In this study, welding strength and distortion have been investigated for AH36 ship steel plate joined by submerged arc welding method. In this context, 18 experiments have been conducted using two different gap sizes, with ceramic back plate and double-sided welded without ceramic under the same welding groove, and also different welding methods, currents, welding speeds, and voltages. All welding grooves of samples were prepared as 45° V type after computer numerical control (CNC) cutting. Specimens for mechanical tests were cut with abrasive water jet cutting technique in order not to affect the weld metal and heat-affected zone. According to tensile test results, fractures in all specimens occurred outside the welding zone of the base metal. It was concluded that double-sided welding method increases the welding strength. 1. Introduction Despite the availability of other transportation methods such as land and air transportations, marine transportation is one of the most preferred and widely used transportation methods in the world due to its economic advantages. Today, more than 95% of world's trade is still provided by marine transportation (Yilmaz & Tümer 2009). Therefore, manufacturing ships is crucial, and the most preferred production type is welded joints. In this respect, high weldability of the material used in ship construction has vital importance (Ay et al. 2003). The shipbuilding industry requires technological advances, such as research in welding techniques and selection of appropriate materials, to reduce processing time and costs without impairing the desired mechanical properties. Recently, researchers have focused on research and development of high-strength low-alloy (HSLA) steels, as well as the investigation of various factors that influenced their weldability (Ribeiro et al. 2016). Many different types of steel, particularly plates of A grade steel, are used mostly in shipbuilding. The quality, security, and costs of metallic ships mostly depend on the design and mechanical properties of the welded joints of ships (Yilmaz & Türner 2009). In ship construction, welded joints are regarded as weak and critical regions (Özden 2003). As some features such as higher welding penetration, corrosion and fatigue resistance, and surface quality of welded joints are to be considered in ship construction, submerged-arc welding (SAW) is one of the most critical welding processes accepted in the world (Asarkaya 2004).

Despite the availability of other transport methods such as land and air transportations, marine transportation is the most preferred and widely used transportation method in the world because of its economical advantages. In service, ships experience cyclic loading. Hence, it can be said that fatigue fracture, which occurs due to cyclic loading, is one of the most critical failure modes for vessels. Accordingly, this makes fatigue failure prevention an important design requirement in naval architecture. In general, a ship structure contains many structural components. Because of this, structural modeling typically relies on Finite Element Analysis (FEA) techniques. It is possible to increase fatigue performance of the ship structures by using FEA in computer aided engineering environment. Even if literature papers as well as rules of classification societies are available to assess effect of fatigue cracks onto the whole ship structure, analytical studies are relatively scarce because of the difficulties of modeling the whole structure and obtaining reliable fatigue life predictions. As a consequence, the objective of this study is to improve fatigue strength of a mercantile vessel against fatigue loads via analytical method. For this purpose, the fatigue life of the mercantile vessel has been investigated. Two different type of fatigue assessment models, namely Coffin-Manson and Morrow Mean stress approaches, were used and the results were compared. In order to accurately determine the fatigue life of the ship, a nonlinear finite element analysis was conducted considering plastic deformations and residual stresses. The results of this study will provide the designer with some guidelines in designing mercantile vessels.