## 5 Conclusions  
Initially, for the preliminary design, the macro-structural analysis should be carried out on the scantling of the panel structure, using a Classification Society guideline. Then, a microstructural analysis of the laminate sequence should be carried out using a \"critical layer\" analysis. Finally, the hybrid tubular joint is dimensioned as an additional reinforcement of the panel, according to the forces acting on the hybrid joint. The number of laminate layers on the tubular reinforcements depends on the type of design load that are applied or transmitted to the panel and/or tubular hybrid joint; thus, the laminate scantling should be validated by the failure criteria using the interlaminar stresses. The model considerations are applicable for the interlaminar study but do not include the calculation of the temperature or hygroscopic effects. Another aspect is the tubular laminate bevelling, as the maximum resulting stresses are located at the reinforced laminate ends. For this reason, we recommend that the level guide proposed by SSC-Lloyd's Register be applied. The proposed moment formula is recommended for tubular reinforcement. In the case where it is necessary to apply another structural reinforcement type, the formula must be modified, the compatibility and stresses between laminates should be analyzed. The interlaminar stresses resulting from the outer layer are related to the possibility of debonding; however, in the case of sandwich panels as a second stage, we recommend analyzing the interlaminar and intralaminar stresses of all layers and the core. In no case, the core should be used perpendicular to the stress direction. When comparing the interlaminar stress fraction recommended by SSC-Lloyd's Register with that proposed by [PERSON], this fraction corresponds to \(10^{6}\) lifecycles, assuming that the core tie layer is CSM. Additionally, [PERSON] proposed that the fraction may also have lower values than those recommended by SSC-Lloyd's Register, depending on the fatigue applied. For this reason, we recommend researching the variation of the interlaminar stress fraction as a function of fatigue. The formulas proposed for the shear and normal stress estimation showed satisfactory results when compared with the values obtained with FEA. The proposed methodology made possible the study of the behavior of the stresses obtained at the adhesive ends and the analysis of the resulting interlaminar stresses that are generated in the adherent's adjacent outer layer. The stress analysis in of the remaining layers and the interlaminar effect on the core, is beyond the scope of this investigation, however, is an important topic of study in the future. For the proposed equations, the failure stresses for laminates of polyester resin with E fiberglass (FRP) are presented in Table 1.  
The proposed methodology is aimed to facilitate the preliminary design of a tubular hybrid joint. The joint as designed allows to join the FRP panel with metal decks having the advantage of getting a watertight union, improving the contact area of the adhesive, and obtaining an inert hybrid metal structure, having as an additional advantage that, depending on the type of load condition on the FRP panel and steel deck, it is easy to increase the number of vertical reinforcements or the adhesive joint length. F.D. : introduction, summary, writing, methodology, tables, figures, validation of results, discussion. L.C. : work structure, discussion of results and conclusions. All authors have read and agreed to the published version of the manuscript. This research received no external funding  
The authors thank the ESPOL Polytechnic University, Escuela Superior Politecnica del Litoral, Faculty of Maritime Engineering and Marine Sciences (FIMCM), for the facilities provided with the laboratory. The authors declare that they have no known competing for financial interests or personal relationships that could have appeared to have influenced the work reported in this paper. _Appl. Sci._**2020**, _10_, 3962