# Maintenance Time Prediction for Predictive Maintenance of Ship Engines
## 2 Materials and Methods  
### Experimental Equipment  
The research ship was a 10,000-ton ship equipped with various technologies, including a dynamic positioning system and a controllable pitch propeller. The ship, whose specifications are detailed in Table 1, also had a propulsion engine with a rated power of 6618 kW and a cruising speed of 17.7 knots. The target engine was a ship GE with a rated power of 1120 kW. It was a 900 rpm, constant-speed four-stroke diesel engine. The generated electric power is supplied to the ship's main switchboard, which distributes electricity to various systems and equipment essential for ship operations. Depending on ship type and operation scenario, three to four generators are typically installed to flexibly manage power demand. Fuel supply is controlled via a governor to adjust the engine load accordingly. Normally, only one generator is operating during normal navigation, considering the operating time; one to three generators are operating in parallel during port entry and exit, berthing, and canal transit, and the engines are immediately used during port entry/exit and equipment loading/unloading. During navigation, the engine load fluctuates frequently due to systems that are repeatedly switched on and off according to the operating conditions, such as air compressors and the compressors used for air conditioners and refrigerators. Frequent load fluctuations also occur during port entry, port exit, and berthing due to port entry/exit operations and equipment loading/unloading. The detailed specifications of the GE are in Table 2.  
Figure 1 shows the schematic structure of data acquisition from the experimental ship's generator engine and the simulation-based learning data. Operating information from the generator engine is acquired via various sensors installed during ship construction, as designated by the shipyard and engine manufacturer. These sensors transmit data through an I/O module to the alarm monitoring system (AMS) located in the engine control room, where they are monitored and stored. The dataset consists of 42 types of time-series numerical data, including cylinder exhaust gas temperature, power, scavenge air pressure, and temperature, all recorded at 10 s intervals during ship operation. \begin{table}
\begin{tabular}{c c} \hline
**Description** & **Specification** \\ \hline \hline Type & HiMSEN 6H21/32 \\ Manufacturer & Hyundai heavy industry, Ulsan, KR \\ Rated output & 1120 kW/900 RPM \\ Number of cylinders & 6 \\ Cylinder diameter & 210 mm \\ Stroke & 320 mm \\ Compression ratio & 17:1 \\ Mean effective pressure & 22.5 bar \\ Maximum cylinder pressure & 179 bar \\ Turbo charger & ABB, 1 \(\times\) A135-M65 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Specifications of generator engine (GE). \begin{table}
\begin{tabular}{c c} \hline
**Description** & **Specification** \\ \hline \hline Gross tonnage (GT) & 9196 tons \\ Length overall (LOA) & 133.0 m \\ Breadth (Milb) & 19.4 m \\ Speed (design draft, 85\% MCR with 15\% SM) & 17.7 knots \\ Range of endurance & 14,500 n.miles \\ Power of propulsion engine & 6618 kW/146 RPM \\ Controllable pitch propeller & D 4000 MM \(\times\) 4 blades, Wartsila, Helsinki, FIN \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Specifications of research ship. Based on the specifications of the real generator engine, a digital asset was constructed using AVL CRUISETM M (R2021.1) to simulate abnormal operating conditions. The system consists of a data acquisition module that collects engine condition parameters (e.g., RPM, torque, exhaust gas temperature, maximum combustion pressure) based on the real ship generator engine. These data are utilized to configure a 1D engine simulation model, which includes major subsystems such as the turbocharger, fuel injection system, scavenge air path, and load profiles. The simulation was used to generate additional abnormal conditions data for model training.