İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Gemi ve Deniz Teknoloji Mühendisliği Anabilim Dalı
Açık deniz tipi balıkçı teknesinde yumrubaş dizaynı
Bulbous bow design for sea going fishing vessels
Ahmet Mertcan Yasa
Uzun yıllardan bu yana denizcilik ile uğraşmış olan Türk toplumu, etrafı denizlerle çevrili olmasına rağmen, denizcilik alanında bir çok ülkenin gerisinde kalmıştır. Son yıllara baktığımız zaman Türk kıyıları ve sahillerinde balıkçı ve de gezi teknelerin de hem sayı hemde tonaj olarak gözle görülür bir artış olduğunu gözlemlemek mümkündür. Özellikle açık deniz balık avcılığı konusunda Türk Balıkçı Filosu oldukça zayıf kalmış ve halihazırdaki tekneler iç denizlere uygun bir şekilde dizayn edildiklerinden bulundukları alanların dışına avlanmak için pek çıkmamışlardır. Türkiye?de deniz balıkçılığı temelde kıyı ve yakın sahil balıkçılığı şeklinde olup tekneler bu tip avlanmaya daha uygundur. Bu tip tekneler de açık deniz için yeterli performansa sahip değildirler. Bu açıdan bakılarak Türk Tipi balıkçı teknesi türleri üzerindeki çalışmanın eksikliği üzerine gidilmiştir. Daha önce bu konuda yapılmış olan Türk Tipi Balıkçı Teknesi İÇTAG I243 projesinden yola çıkarak, elde edilmiş olan form üzerinde daha az dirence sahip ve de daha hızlı tekneleri verecek olan yumrubaş uygulamaları ve dizaynı incelenmiştir. Bilindiği gibi yumrubaş gemi etrafında oluşan dalga profilini değiştirerek, dalga direnci üzerinde azaltıcı rol oynamaktadır. Her ne kadar balıkçı teknesi de olsa düşük direnç her zaman için aranan bir nitelik olmuştur. Dirence ek olarak, açık denizlerde avlanması öngörülen bu tip tekneler için yumrubaş uygulaması ve dizaynı sırasında sadece dirence bakılmayacak aynı zamanda elde edilen farklı formlar üzerinde stabilite ve denizcilik hesaplamaları yapılmak suretiyle balıkçı teknesinin form yapısı da incelenecektir. Bu çalışmada öncelikle Türk Balıkçı Filosu ile ilgili genel bilgiler verilmiş ve eksik yönleri üzerinde durulmuştur. İÇTAG I243 projesinde elde edilmiş olan optimize balıkçı formu üzerinde çalışmalar yapılmak suretiyle toplamda 36 farklı yumrubaş modellenmiş ve bu yumrubaş türleri ana form üzerine eklenerek incelenmiştir. Direnç, stabilite ve denizcilik yönünden bu formlar birbirleri ile karşılaştırılmıştır. Direnç açısından en iyi ve en kötü formlar seçilerek kazanç ve kayıplar ortaya konmuş ve sınırlar belirlenmiştir. İkinci olarak seçilen en iyi formlar arasında stabilite hesapları yapılmış ve yumrubaşın stabilite üzerindeki etkisi incelenmiş ve etkilerinden bahsedilmiştir. Üçüncü olarak yine aynı formlar üzerinde Akdeniz göz önüne alınarak denizcilik hespları yapılmış ve denizcilik yönünden hangi formun daha iyi sonuçlar verdiği ve karşılaştırmalar bu çalışmada yer almıştır. Çalışma neticesinde modellenmiş formlar arasından en uygun formun seçilimi tamamlanmış ve geleceğe yönelik çalışma ve önerilerden bahsedilmiştir. Bu çalışma ile Türk Tipi açık deniz balıkçı teknesi üzerinde yumrubaş uygulamaları incelenmiştir. Bu inceleme dizayn hızı temel olacak şekilde direnç, stabilite ve denizcilik hesaplarını kapsayacak şekilde yapılmış olup balıkçı tekneleri için yumrubaş uygulanmasının etkinliğine bakılmış ve elde edilen yumrubaşlı formlar arasından en iyi tek bir formun seçilmesi amaçlanmıştır. Her bir inceleme konusu için farklı yumrubaş türleri farklı sonuçlar vermiştir. Gerek direnç, gerek stabilite, gerekse denizcilik hesaplarında olsun farklı tipteki yumrubaşların etkileri beklendiği gibi farklı sonuçlar vermiştir. Bu çalışma ile açık deniz tipi amacı ile tasarlanmış olan balıkçı formuna uygulanan yumrubaşlar arasından yapılan incelemeyle bir form belirlenmiş ve kısa vadede ilk amaç gerçekleştirilmiş olmuştur.
It is a well known fact that Turkish Society has not been performed well on fishery although subject country has more than enough in land waters and seas around. Particularly, Turkish Fishing Fleet underperforms at open sea conditions. As mentioned in project ICTAG I243, in Turkey fishing has been mostly practise as sea-shore and coastline fishery. Most of the vessels in Turkish Fishing Fleet has not enough sea worthiness characteristics for deep water fishery. If we check the international fishery statistics, it?s clear that the 80 millions tons of fish annually, and Turkey has very small percentage on it. Although there has been improvements on new vessels in recent years, Turkish Fleet still is not capable of going on open sea. Turkish Fleet characteristics has been supporting this situation. In 2012, there are only 225 vessels having higher than 30 meters overall lenght. It is very small amount inside 20.100 vessels. This situation clearly shows that Turkish Fishery is imprisoned inside their shores. To change and improve this situation, in this paper, sea going fishing vessel is focal point. To start this paper, parent form is necessary to work on it. Therefore, after several researchs, parent form has been found. Previosly done project ICTAG I243 aims to improve classical Turkish Fishing Vessel for sea worthiness characteristics and designed a new hull form with improved characteristics. Grounding on this vessel form, in this paper bulbous bow designs has been carried on. In total, there are 36 different bulbous bow designs with 4 different bulbous bow sections. All those bulbous bow designs has been compared according to how good on resistance charactericits, how they impact on stability and how they change sea worthiness characteristics. All calculations has been done using ?Maxsurf? and form designs has been done using ?Rhinoceros 4.0?. On first part of this paper, Turkish Fishing Fleet has been described and explained its characteristics. In recent years, it well noticable fact that Turkish Fleet has expanded in large number. However, when the characteristics have been checked, most of the fleet is more suited for shore, inland sea fishery. There are very few vessels are suited for open sea fishery. From the tables, there are approximately 20000 vessels in Turkish Fishing Fleet and nearly 15000 of them have overall lenght not more than 12 meters. It can be say that Turkish Fishery has been limited to its shores. To change this situation, firstly TUBITAK ICTAG I243 project has been made. Prof. Dr. Abdi Kukner as a project leader carried out this research and created a new hull form generated from classical Turkish Fishing vessel form. By doing that, new hull form is more suitable for open waters and sea worthiness characteristics have been improved significantly. On second part, bulbous bow describtion has been made. When historical development process has been examined for bulbous bow, all started with ram bows as a weapon. Especially in ancient Greek, ram bows had been used as a weapon in great numbers. If we keep going on in history, in 1778 Charles Bossut had been discovered another use of bulbous bow. Although researches have been stated with just curiousity, later he discovered that bulbous bow can cause lesser resistance values on ships. Later on, in 1867, W. Froude again had made researches about bulbous bow and tested on his two models named Raven and Swan. He noticed that model with bulbous bow has lesser resistance and then he made hundreds of models tests and studied on wave making resistance. In 1905, this time Taylor handle Froude?s work and he designed first ship with bulbouw bow, Delaware. In history, there are many studies have been placed in literature and all studies are still going on at the present time. Modern bulbous bow has been developed by T. Inui as knows also ?father of bulbous bows?. T. Inui applied bulbous bow to all kind of ships such as motoryacths and supertankers. Also, Inui mostly focused on wave pattern generated by hull in water. Bulbous bow changes the wave form which is generated due to movement of ship on its hull and this causes less wave resistance on hull. The effect of bulbous bow occurs on wave pattern generated by hull form. Bulbous bow effects wave pattern by damping its amplitude and thus smaller resistance can be achieved by small wave form through the hull. An experiment has been made to prove this effect. A sphere fully submerged in fluid moving with a speed and a negative pressure area occurs around the sphere which is damping the wave profile. Experiments showed that bulbous bow is most effective when Froude Number is between 0.24 and 0.56. Bulbous bow can be grouped in three different types. First one is delta-type bulbous bows. Second one is ellipse (circular) type bulbous bows and last one is nabla-type bulbous bows. This types are in connection with cross section of bow. The shape of cross section of bow, determines the type of bulbous bow. On third part, mathematical theory has been explained. The components of total resistance are friction resistance, viscous resistance and wave resistance and also other components are residual resistance and friction resistance. In this part, components are explained. In this paper, for friction resistance, ITTC?s formula has been used. As mentioned before, bulbous bow changes the wave form on hull and this effect is similar to damping effect. Therefore, wave forms have been expained detailed in every way. On fourth part, main charateristics of hull form has been explained. Overall Lenght is 33.7 m and breadth is 8.96 m and draught is 2.5 m. All graphical designs have been carried out by using Rhinoceros 4.0. As mentioned before, there are 3 types of bulbous bows. In this paper, 36 different bulbous bows have been designed as 4 types. As they are delta type, nabla type, circular and ellipse types. This is because circular and ellipse type studied as different forms, although they grouped as one in Kratch?s Method. While designs doing, there are some key points followed. Firstly, it?s important to keep buttocks undisturbed. Secondly, in design process, all design and fairing work should be done on one view to provide adaptability on maximum level. Also, waterlines should stay undistubed. The ther one is, all design work must be limited to only bow and should not affect aft or mid parts of ship. Additionally, Cp should keep fixed (or very small changes) if possible. Deadrise angle should not be changed and bow form of hull should stay the same until design water line. All these guidelines also showed on hull forms and sections as images in this thesis. On this part also design notations have been explained. For delta types D-X, for ellipse and circular E-X and EO-X and for nabla N-X parameters are used. X here defines the sub-type of bulbous bow. On last part, comparison for resistance, stability and sea worthiness has been made. For resistance, Holtrop-Mennen Method is used. Although there are several more methods, Holtrop Mennen Method is more efficient and effective than other methods. Resistance comparison carried for 10, 11, 12, 13 and 14 knots. Despite the calculations are made for each speed differences, however, final choice is made for 12 knot which is design speed. While doing this, not only good forms have been chosen but also forms have bad impact on resistance also considered. By doing so, a range for resistance comparison has been obtained. In total 12 designed forms have been chosen as good ones and bad ones to draw a range. Comparison is made for total resistance, residual resistance coefficient and differences and resistance gains stated as percentage. Also wave profiles created and made another comparison between them. In this way, resistance calculations are supported with wave profiles comparison. For stability, only 7 forms included in comparison, because only 7 of 12 forms had good impact on resistance. So, we can choose the best form out of resistance and stability comparisons. Stability curves are calculated for all forms and KG, KM, GM, KB, BM values are calculated. It should be mentioned that KG values are not given in ICTAG project so to obtain KG values, weight distribution has carried out to calculate KG. Max GZ and its degree is calculated to make good comparison. At last, sea worthiness comparison is conducted. It is divided into two different parts to make effective comparison as heave and pitch motions. First, selected 7 forms has been studied for their heave characteristics. Secondly, same forms studied for their pitch characteristics. It?s known that bulbous bow have different effects on pitch and heave therefore, comparison is made into two parts. After all comparisons are done, final forms are located in table and one form is selected as the most suitable bulbous bow form for Turkish Fishing Vessel Form. In this thesis, Bulbous bow applications on Turkish Form Fishing Vessel has been conducted and in principle 3 different points are compared as resistance, stability and sea worthiness characteristics. On desing speed, D-Mİ form and E-115 form gave the best results for resistance. Secondly, for stability, D-Mİ form has gave the best results and as mentioned before, sea worthiness divided into two categories. For heave, D-Mİ gave the best results and for pitching, E-115 is the best form. However, our aim is to chose the best form inside all of these calculations, not only one way. When we check, D-Mİ form gave the best results for resistance, stability and heave, this means this form gives the best 3 results of 4 different aspects. On the other hand, stability and sea worthiness characteristics results showed that the bulbous bow has very little effect on stability and heave and pitch values. In this regards, it is also to keep in mind that the E-115 which is the best for resistance values so, for further research, this form also should be considered. For future work, bulbous bow applications on stern of ship will be carried out to minimize the wave profile and amplitude on ship. Also, more powerful and accurate calculations should be carried out with CFD. This is not carried out because of the time lag. With this thesis, our aim is achieved and we chose a fishing vessel form which is the best form for stability, resistance and sea worthiness characteristics.