Sea-wave dynamic loading of sailing yacht's retractable keel/Dinamicna obremenitev valovanja morja na dvizno kobilico jadrnice

A highly specialized analysis of functionality of a retractable keel lifting mechanism is presented in the paper. Because of its special design a retractable keel is vulnerable to rough sea conditions. To alleviate possible malfunctions or even damage to the keel, an analysis of lifting the keel during rough sea (WMO sea state 6) is performed. Reliable estimation of load acting on a keel is crucial for the subsequent functional or structural analysis of the keel. Aiming to obtain these loads, a sea wave analysis is performed first, where a wave train is determined by respecting statistical data regarding the required sea condition. Two wave cases are considered: head seas (waves coming from the front) and beam seas (lateral waves). A deterministic dynamic analysis on the wave-hull-keel system is then performed. The response of this system is obtained in the form of a time dependent acceleration of the centre of gravity of the vessel and in a time dependent lifting force, i.e., the force which is required for lifting the moveable part of the keel during rough sea. Finally, the required pulling force of the lifting mechanism is determined. Keywords: sailing yacht, retractable keel, wind wave, computer simulation Kobilica na sodobnih jadrnicah je oblikovana v obliki navpicno stojecega krila simetricnega prereza, ki sega globoko pod trup jadrnice. Obicajno je na spodnjem koncu krila dodana se utez, prav tako hidrodinamicno oblikovana, s katero zmanjsujejo nagib jadrnice, ki je posledica delovanja sile vetra na jadra. Globoko segajoca kobilica in utez je seveda primerna za jadranje, obenem pa onemogoca vplutje v plitkejse zalive in pristanisca. Z namenom ohranjanja obeh zazeljenih lastnosti, t.j., kvalitetnih jadralskih sposobnosti in dostopnosti v plitkejse vode, so razvili razlicne vrste dviznih kobilic. Poseben tip dviznih kobilic je t.i. teleskopska kobilica, ki je pritrjena na trup s spodnje strani in, za razliko od obicajnih dviznih kobilic, katerih dvizni jasek zaseda znaten del bivalnega dela v trupu jadrnice, ne sega v notranjost trupa. Oblikovanje in dimenzioniranje kobilice je zahtevno projektantsko delo, tako s podrocja optimizacije hidrodinamicnih razmer, kot tudi z vidika ohranjanja mehanske integritete in zagotavljanja funkcionalnosti kobilice. Ker pa je po svojem nacinu delovanja teleskopska kobilica v bistvu mehanizem z masivnimi gibajocimi deli, ki mora pravilno delovati tudi pri surovih pogojih dela na morju, je projektiranje se toliko bolj z