Hasarsız Stabilite Kriterlerinin Karşılaştırmalı Değerlendirilmesi

Abstract

Günümüzde ticari gemilere uygulanan stabilite kriterlerinin gelişim süreci eski tarihlere dayanmasına rağmen, bunun yazılı kural haline getirilmesi 1960’lı yıllarda olmuştur. Gemilerde ilk resmi Uluslararası stabilite kuralları IMO (International Maritime Organization) A.167 önergesiyle 1968 yılında uygulanmaya başlanmıştır. Temel olarak bu önerge, gemilerin başlangıç metasantr yüksekliği ve doğrultucu moment kolu eğrisi altında kalan alan değerleri için bazı kriterleri içermekteydi. Gemilere etki eden dış unsurlarla ilgili herhangi bir parametre dikkate alınmamakta idi. Bundan dolayı, IMO 1985 yılında A.562 önergesiyle, gemilerin yalpa ve rüzgarın bileşik etkisi altındaki durumunu inceleyen hava kriterini yürürlüğe koymuştur. 1993 yılında ise daha önceki önergeleri A.749 önergesinde toplayarak, bu kriterlerin, 24 metre ve daha büyük tüm gemilere uygulanmasını zorunlu hale getirmiş ve daha önceki önergeleri yürürlükten kaldırmıştır. Daha sonra, A.749 önergesi 1998 yılında “Intact Stability (IS) Code” (Hasarsız Stabilite Kodu) olarak güncellenmiş ve 2008 yılında nihai halini almıştır. Ancak askeri gemilerde, ticari gemilerde olduğu gibi uluslararası kabul görmüş ve bütün ülkelerin kullandığı kurallar bulunmamaktadır. Genellikle ülkelerin kendi donanmalarına ait kullandığı kurallar bulunmaktadır. Ancak, birçok ülkenin askeri gemi kurallarının çıkış noktası 1944 yılındaki bir faciaya dayanmaktadır. 1944 yılında Amerikan donanmasının Pasifik Okyanusunda tropik bir fırtınaya yakalanması sonucunda kısa süre içinde 3 adet destroyer batmış ve dördüncüsü de bacasının rüzgar basıncı altında kırılması sayesinde kurtulmuştur. Bu facia, Amerikan donanması için stabilite kurallarının geliştirilmesinde etkileyici rol oynamıştır. Ilk kurallar 1962’de Sarchin ve Goldberg tarafından yayınlanmıştır. Bu kurallar diğer ülkelerin donanmaları tarafından adapte edilmiştir. Askeri gemilerin stabilitesi amaçları gereği büyük önem taşımaktadır. Çünkü geminin hem gerekli stabilite kurallarını sağlaması, hem de görevini yerine getirecek kabiliyette olması gereklidir. Görevini yerine getirirken herhangi bir zafiyete uğramaması gerekmektedir. ANEP 77 hasarsız stabilite kodu ile amaçlanan, NATO’ya üye ülkeler ve bu kodu kullanmak isteyen diğer ülkelerin inşa edecekleri askeri gemiler için ortak bir standart oluşturmaktır. Bu çalışmada da ANEP 77 askeri gemi kodu ile dünya genelinde kullanılan Alman askeri gemi kodu olan BV 1030-1, İngiliz askeri gemi kodu olan NES 109 ve ticari gemilere uygulanan uluslararası stabilite kodu olan 2008 IS kod’un hasarsız stabilite kriterleri ve hangi yatırıcı moment kollarının nasıl hesaplanacağı ile ilgili bilgiler verilmektedir. Böylelikle genelde uygulanması amaçlanan bir kodun mevcut kodlarla karşılaştırması elde edilecektir. Sonuçlar bölümünde yukarıda belirtilen 4 adet kodun bir ticari kuru yük gemisi ve 2 adet savaş gemisi üzerinde uygulanması ve karşılaştırmalı sonuçları verilmektedir.

Stability is one of the most important safety features of ships, and in particular of small ships which tend to suffer from insufficient stability which could lead to the capsizing of the vessel and loss of lives. It is, therefore, essential to design a ship with adequate stability and to maintain it in all conditions of loading during its operation. Development of the concept of metacentric height apparently originated with Bouguer in 1746. Derivation and calculation procedures for the righting lever curves were published by Atwood in 1796. Development of quasi-dynamic stability and the concept of the energy balance method was advanced by Moseley in 1850. Several proposals for the use of a GM based stability criteria were offered in the late 1800s, and proposals for criteria based on righting energy have existed since early 1900s. The major historical work on the stability of ships was carried out by Rahola in 1939. Rahola’s work involved a detailed analysis of Baltic ship capsizings and included a proposal for a GZ based criteria. Wind heeled GM requirements have been applied in the US since the 1940s and became a US requirement for cargo ships in 1952. Based on recommendations from the 1960 International Conference on the Safety of Life at Sea (SOLAS 60), the IMCO sub-committee on Subdivision and Stability was formed in 1962. The first international stability criterion, Resolution A.167, largely based on Rahola’s GZ criteria, was adopted by the IMO in 1968 for ships under 100m. The IMO assembly adopted Resolution A.562 in 1985. This resolution was an energy balance criterion, and also included a wind heeling recommendation, and was to be used as a supplement to A.167. The IMO assembly adopted Resolution A.749(18) on 4 November 1993. (Code on Intact Stability for all Types of Ships Covered by IMO Instruments). Intact Stability Code (IS Code) have been used since 1 July 2010, instead of A.749(18). This historical development is related to the merchant ships intact stability criteria. For merchant ships today, stability is regulated by the criteria and rules issued by the International Maritime Organization (IMO). Although IMO only recommends the fulfilment of some of these criteria, usually all newbuildings have to meet the requirements as they are made mandatory by the respective flag state authorities. Intact stability for naval ships is more important and crucial than the merchant ships. Naval ships are different as compared to merchant ships by the construction and purpose of use. Generally, naval ships are more damage resilient and armed with weapon systems. For the intact stability of naval ships, there are no internationally agreed and applied rules. Each country uses their own naval ship rules which reflect their needs. The most known naval rules are BV 1030-1 rules of Germany and NES 109 rules of the United Kingdom. The primary starting point of the most of naval ship rules was the typhoon of December 1944. The US Pasific fleet was caught in a major tropical typhoon and many ships were lost. After this disaster, first rules were published by Sarchin and Goldberg in 1962. The International Naval Safety Association (INSA) was established in April 2008 in order to develop and maintain the Naval Ship Code. INSA is a group consisting of navies and classification societies. The UK MoD is one of the founding members of INSA. The Naval Ship Code (NSC) is a goal based standard that determines a minimum level of safety for naval vessels. It is the formal document published by NATO (as ANEP77) which includes the Code and supporting Guide. The overall aim of the Naval Ship Code is to provide an internationally accepted standard for naval surface ship safety based on and benchmarked against IMO conventions and resolutions that embraces the majority of ships operated by the Navies. The basic principle of a goal based approach is that the goals should represent the top tiers of the standards, against which ship is verified both at the design and construction stages, and during ship operations. A “goal-based” standard, rather than relying on the existing rules, considers what the ultimate safety objective of the designer might be, and will consider a range of alternative design approaches that will reach this desired goal. Thus, whereas in the past the rules would have been specific over every detail, now, the over-arching objectives will be specified, giving the designer choice, and the freedom to innovate. A general information about “The Naval Ship Code (ANEP 77)” is given in the second chapter. In the third chapter, general information about “BV 1030-1” is presented. BV 1030-1 is the stability criteria which is applied to German naval ships. The rules are applicable to the monohull naval surface ships. Kurt Wendel first drafted the stability regulations for the German Federal Navy in 1961. Wendel issued a new edition of the regulations known as BV 1033 in 1964. An early detailed explanation of the regulations and their background is due to Arndt (1965). His paper was soon translated into English by the British Ship Research Association and appeared as BSRA Translation No. 5052. An updated version of the regulations was published in 1969 and since then they are known as BV 1033. As pointed out by Brandl (1981), the German regulations were adopted by the Dutch Royal Navy and they also served in the design of some ships built in Germany for several foreign navies. The rules were finally revised and published in 2001 as BV 1030-1. In the third chapter, the information about the operational areas, loading conditions, obtaining the righting and heeling arms and intact stability requirements are given. In the fourth chapter, general information about “NES 109” is given. NES 109 is the stability criteria applied to the UK naval ships. The stability standards of the Royal Navy evolved from the criteria published by Sarchin and Goldberg in 1962. The first British publication appeared in 1980 as NES 109. The currently valid version is Issue 4 (MoD, 1999a). The British standard was issued by the Ministry of Defence (MoD) and is applicable to vessels with a military role, to vessels designed to the MoD standards but without a military role, and to auxiliary vessels. The vessels with a military role are those exposed to enemy action or to similar dangers during peacetime exercises. The standard NES 109 has two parts; the first is dealing with conventional ships, the second is with unconventional vessels. The second category includes; monohull high speed vessels, multihull vessels and dynamically supported vessels. In chapter four of this study, the provisions for conventional vessels are presented. These provisions include the operational areas, moment arms, stability criteria and loading conditions. In the fifth chapter, general information about “2008 IS Code” is given. 2008 IS Code is the most recent stability criteria of IMO for the merchant ships. The purpose of the Code is to present mandatory and recommended stability criteria in a single document and other measures for ensuring the safe operation of ships, to minimize the risk to such ships, to the personnel on board and to the environment. The Code has two parts. The mandatory requirements are given in part A and recommended provisions are given in part B. Although part B is recommended in nature, classification societies and flag states apply this part as mandatory. This code is applicable for cargo ships, cargo ships carrying timber deck cargoes, passenger ships, fishing vessels, special purpose ships, offshore supply vessels, mobile offshore drilling units, pontoons and cargo ships carrying containers on deck and container ships of 24 m in length and above. In chapter five, the calculation details and assumptions related to loading conditions and stability criteria are presented. In chapter six, the application of ANEP 77, BV 1030-1, NES 109 and 2008 IS Code to an ocean going general cargo ship, a navy surface combatant and an auxillary type naval vessel is given. The full load departure and full load arrival loading conditions of each vessel type are taken into account in the analyses. For each loading condition, hydrostatic particulars, righting arm (GZ) curve, wind heeling moment arms according to the codes, heeling arms due to turning and passenger crowding and evaluation of stability criteria are presented in this chapter. In chapter seven, results and overall assessments are presented. According to the results, it couldn’t be said that one code is the best and applicable to all ships. Each code has its own positive or down sides. For example; if the wind pressure is taken equal in each code, 2008 IS Code has the most stringent weather criterion. However, the assumed wind speed according to the operational areas is different. In this case, ANEP 77 is the most stringent, because the wind speed is 100 knots for the unlimited ocean going operational area. In another case, if NES 109 and 2008 IS Code are compared, NES 109 has the most stringent criteria in terms of the area under GZ curve criteria and probably application of NES 109 to merchant ships is impractible. Consequently, ANEP 77 and NES 109 resemble each other in general. Area under GZ curve criteria are eliminated in ANEP 77. Each heeling arm is compared with the respective righting arm. In this case, if the operating conditions are defined well, ANEP 77 offers a large working area to designers.