Selection of the bow for tuna purse seiners

The paper is devoted to the issue of designing the hull shape of mo-dern tuna seiners for ocean fishing. The applicability of modern non-standard shapes of bow tips to tuna fishing vessels is considered. The expediency of preserving the classical hull shape for a tuna seiner has been substantiated – an inclined stem with a bulbous bow in the underwater part. The analysis of the existing scientific and technical groundwork in the design of the bulbous bow extremities has been carried out. It has been revealed that 3 main types of bulbous are used – "delta" (∆-type), elliptical shape (O-type), "nabla" (∇-type), and 6 bulbous parameters (linear and nonlinear) that affect the shape of the tip have been determined. It has been shown that the Kracht diagrams, the main published method for designing bow, cannot be fully applied to modern tuna seiners, since the ranges of variation of the bulb parameters go beyond the diagrams. To solve the problem of designing the optimal shape of the hull, it has been decided to develop a series of theoretical drawings (TD) of vessels with variations in the parameters of the bulba. TD development has been carried out on the basis of a tuna seiner of the B-406 project, of the Rodina type. The characteristics of bow of the constructed tuna seiners have been used as the initial data for designing the shape of the nasal bulba. As a result of combining the parameters, 192 variations of the bulb have been obtained. The method of conducting further studies of seaworthiness in order to find the optimal shape of the bow of the hull is described. Minimization of the coefficient of residual drag in calm water and rough seas, as well as minimization of vertical accelerations at specified points of the vessel, are accepted as optimization criteria.