## 1 Introduction
For example, the high running temperature of the reformer, approximately 873 K in the cited work; the need for a scrubber to filter impurities that can reduce the fuel cell performance; or the slow system response to power demand changes. One alternative to PEMFCs or SOFCs are Direct Methanol Fuel Cells (DMFCs). No reports are known on the use of DMFCs on-board AUVs, but DMFCs have a number of advantages that favour their use in powering AUVs. On the one hand, methanol is a well-known alcohol that is a liquid under ambient conditions of pressure and temperature thereby facilitating its storage and handling. On the other hand, methanol is used directly in a DMFC without the need to reform it, and it generates water and CO\({}_{2}\) as the main reaction products [14]. Despite the lower efficiency of a DMFC (typically around 25%) compared to that of a PEMFC or a SOFC (typically around 50%) the absence of a reformer and/or complex fuel storage systems simplifies the power plant. This work explores the possibility of powering an AUV with a DMFC-based power plant in order to get longer endurance values than those provided by battery-based power plants. To achieve this, a methodology, based on the comparison between actual AUVs, powered by batteries and Al/HP semi-fuel cells, and equivalent mathematical models, powered with DMFCs, has been followed. For this work, a theoretical design is equivalent to a real AUV if it has the same capabilities regarding sensors, cruising speed, maximum navigation depth, and size. This methodology is considered adequate for the purpose of this work, as the reference AUV establishes a comparison framework under real and fixed conditions. The selected reference AUVs are the HUGIN 1000, HUGIN 3000, and HUGIN 4500, the characteristics of which are summarized in Table 1. These vehicles were selected because detailed information about their payload is publicly accessible [6], and both the HUGIN 3000 and the HUGIN 4500 are some of the commercially available AUVs with the longest declared endurance. Furthermore, these vehicles belong to the same family with similar operational characteristics, but their maximum operation depth and size vary, which allows checking the impact of the size in the performance of the proposed power plant. From hereinafter, the three designs investigated are designated as Model 1000, Model 3000, and Model 4500, respectively. The mathematical model used to generate the theoretical AUVs is based on a genetic algorithm [15]. A genetic algorithm is a type of stochastic evolutionary method that is appropriate for solving multi-objective optimization problems. These algorithms are inspired by the process of natural selection and belong to the class of evolutionary algorithms that are population-based metaheuristic optimization algorithms. They use biology-inspired mechanisms like mutation, crossover, natural selection, and survival of the fittest in order to refine a set of solution candidates iteratively. One example of the application of genetic algorithms to the design of AUVs hull forms can be found in [PERSON] et al. [16]. The structure of this article is as follows. Section 2 describes the quick preliminary design model developed. Section 3 outlines the configuration of the design tool for this work. The results obtained and their discussion are detailed in Section 4. Finally, the conclusions of the work are set forth in Section 5.