In this thesis a numerical calculation of the strength and stability of the keel boat was carried out. The keel model consists of two parts: fin and a keel slider. The keel is made of laminate composite materials. Some basic assumptions and expressions of composite material mechanics, which are used in the work, are presented. The calculation was performed using the Finite Element Method (FEM) in the Abaqus program package. In order to choose the appropriate finite elements for the keel calculations, and to test the convergence of numerical solutions, a verification calculation was performed on a simple supported rectangular plate model. This rectangular plate is made of two unidirectional composite plies made of E-glass and epoxy resin. Convergence has been verified using the classic shell and continuum shell elements. The numerical analysis of the composite keel consists of several iterations, which are used to find and verify the best solutions that will satisfy the strength and stability of the construction. The first iteration consists of a keel calculation in which the material and strength properties are obtained by using micromechanics. In the second iteration, a calculation with properties corrected according to experimentally obtained data is performed. Then, in the third iteration, the problem of stress concentration at the transition from the fin to the keel slider was solved and the solution was given in the form of a radial transition between two parts. The fourth iteration contains a model on which an I-profile fixing was added at the point of contact of the keel with a keel box. Reinforcement is needed to meet the strength criteria of this part of the keel. The last iteration was the addition of fixings with a quadrilateral profile (which follows the hydrodynamic profile of the keel fin) for the purpose of securing the keel stability.