In order to develop the rational finite element models of the high-speed amphibious vehicle bodies in relation to their optimal design, a computed experimental substantiation was performed to select the finite elements (FE) required dimensions on the basis of experimental data obtained from literature and results of the specially conducted experiments. The study made it possible analyze the FE size influence on the computation results accuracy based on simulation in programs for hydrodynamic analysis and computation of the body stress-strain states using the finite element method (FEM). Calculation results were verified using the finite element models with different FE sizes. This paper focuses on the operating modes when moving, as they are the most hard for the body. A motorboat with a hull shape typical for the high-speed amphibious vehicles was selected as the object in computational and experimental research. After comparing main parameters obtained by computation (drag force to motion on water, trim and stress angles in the hull bottom) with the experimental data, it was concluded that FEM makes it possible to obtain calculation results with an acceptable error for the rational and high-precision finite element models. For the amphibious model, the average errors in drag force and trim angle were 5.6% and 12.8%, respectively. For a scale model, the average trim angle error was about 5%. Further research was carried out using the example of computation results for the Froude number of Fr = 3 with the maximum error. After reducing the FE length in the rear body area by 50%, errors of these two parameters were decreasing by 64% and 33%, respectively, which was useful in computation. To solve the problem, finite element models of the low, medium and high levels were compiled. Analysis of the results obtained using the finite element models of these three levels demonstrates that the mid-level finite element models are making it possible to ensure sufficient accuracy with the limited amount of computation time, i.e. it could be considered rational. For this model using the similarity theory, the recommended ratio of the lengths of the FE sides to the length of the body should not exceed 1:200, where the average error in the computation results of the body stress-strain state is no more than 5% compared to the experiment.

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