Data conversion between ship CAD software and hull prescriptive design software is a crucial step in achieving model-based integrated 3D digital design. This paper investigates the requirements and technical pathways for bidirectional data conversion between Smart3D (S3D) and the hull prescriptive design software Mars2000 (Mars). A secondary development of the S3D software was conducted using the VB.NET language. The tool extracts data related to plating, compartments, and longitudinal stiffener connection nodes at transverse section positions from the full ship model through longitudinal range traversal and filtering. Based on custom rules, the extracted data is converted according to the Mars modeling method, and a Mars model file is exported. Subsequently, by comparing files, the tool identifies modifications made in the optimized Mars model and automatically updates the S3D model accordingly. Tests and validations performed on a 114,000 DWT oil tanker demonstrate that the bidirectional data conversion between S3D and Mars is accurate and efficient. The time required for model conversion using the tool is approximately 1/20 of the time needed for manual modeling, and the model update time is reduced to about half of the manual modification time.