## 1 Introduction  
Due to global climate changes, one of the main requirements in the shipping industry is the reduction in fuel consumption and harmful gas emissions, aiming to decrease navigation costs and meet the requirements imposed by the International Maritime Organization (IMO) [1]. Most ships during their service enter restricted waterways, necessitating consideration of the effect of confined and shallow water. To meet the requirements for reduced energy consumption, IMO has proposed trim optimization as a solution, which does not require altering the hull form. Trim optimization can be achieved by ballasting or redistributing the load [2]. When optimizing trim, it is important to understand that the ship will have different total resistances at the same draft and speed for different trims during navigation. Trim optimization can be assessed by towing tank testing or using computational fluid dynamics (CFD). [PERSON] and [PERSON] [3] conducted a study on the total resistance of the container ship for three values of the Froude number and draughts using Reynolds Averaged Navier-Stokes (RANS) simulations. The authors concluded that the optimal trim varies at different draughts and Froude numbers. Initially, they predicted the ship resistance on an even keel and then conducted an optimization procedure, demonstrating that by varying the trim, reduced total resistance of the ship and improved energy efficiency can be achieved. [PERSON] et al. [4] investigated the trim optimization effect on the propulsion characteristics of the ship using model testing. Model tests were conducted for various trims, and the required power was evaluated to investigate the effect of trim on the propulsion characteristics in calm water. The alterations in ship propulsion characteristics concerning trim and draft have been studied, and the trim for which the required power can be reduced was identified. [PERSON] and [PERSON] [PERSON] and [PERSON] (2018) investigated the influence of trim on the total resistance of the KRISO Container Ship (KCS) model and found that with a slight trim adjustment at the stern, the total resistance of the ship decreased by 2.29%. [PERSON] et al. [PERSON] _et al._ (2018) applied a combination of experimental and numerical methods to investigate the total resistance of a 4250 TEU container ship. The authors conducted trim optimization with respect to the total resistance of the ship and concluded that there was a different optimal trim for each draught and speed. [PERSON] et al. [PERSON] _et al._ (2018) predicted that the relative deviations of the total resistance of the KCS ship trimmed by bow at the slow steaming speed are larger for the ballast draught in comparison to the design draught. [PERSON] et al. [PERSON] _et al._ (2018) investigated the effect of trim and draught on the total resistance of the DTMB 5415 ship. The research results indicated that it is possible to achieve a reduction in total resistance of 1.5%, while a reduction of up to 8% can be achieved for pressure resistance. [PERSON] et al. [PERSON] _et al._ (2018) investigated the possibility of fuel savings by employing model testing and field measurements and concluded that in certain cases, trim optimization can reduce fuel consumption. [PERSON] et al. [PERSON] _et al._ (2018) employed experimental fluid dynamics (EFD) and CFD to assess the effect of trim on the total resistance of the ship in the model scale and demonstrated good agreement between the experimental and numerical results. When a ship enters shallow and confined water, the total resistance of the ship increases, which is caused by the smaller under-keel clearance and limited width of a waterway. The flow is accelerated around the hull, which, according to [PERSON]'s principle, results in reduced pressure below and around the hull. These changes lead to additional sinkage of the ship, a decrease in the water level around the ship, and increased wave resistance [PERSON] _et al._ (2018).