Rolling Motion of a Round Bottom Ship (Scale Model) in Different Free Surfaces of a Liquid Cargo

Abstract

Live fish carrier is a common termininology in a carrier or ship which is used to transport live fish from one place to another. The cargoes which mostly consists of water is classified as a liquid cargo. Based on its characteristic, a liquid cargo will always follow the shape of its containers and maintain its flat surface. As a result, position of the centre of gravity in the containers will change easily depending on their movements. Furthermore, it is known that a liquid cargo has free surface which may influences ship stability. Therefore, comparing to solid cargo, a liquid cargo has more negative effects on ship stability. The objectives of this research were, 1) to determine rolling performance parameter influenced by free surface, and 2) to determine the influence of free surface on rolling performance of a ship model. Experimental method was applied in this research by using a ship model. Observation was carried out in order to record the rolling performance of the model as an effect of some variations of fish hold condition and free surface. Based on the result, it can be concluded that the wide of free surface gives impact on ship motions, where the extending of free surface will be followed by the increasing of inclination angle, rolling period, and attenuation time. However, at the same time the frequency of rolling is getting smaller.

Kapal pengangkut ikan hidup adalah kapal yang khusus digunakan untuk mengangkut ikan dalam kondisi hidup dengan muatan utamanya adalah air dan ikan. Jenis muatan kapal ini dikategorikan sebagai jenis muatan cair. Sifat muatan cair berubah bentuk sesuai wadahnya, sehingga titik beratnya selalu bergeser. Kondisi ini dikarenakan muatan cair memiliki free surface. Free surface berdampak terhadap kestabilan kapal. Pergeseran titik berat muatan menyebabkan kapal bermuatan cair menjadi berkurang kestabilannya dibandingkan kapal bermuatan padat. Tujuan penelitian ini adalah : 1) menentukan parameter keragaan oleng model kapal yang dipengaruhi luasan free surface, dan 2) menentukan pengaruh luas free surface terhadap keragaan oleng model kapal. Metode penelitian dilakukan dengan mengamati gerakan rolling model kapal sebagai efek dari keberadaan palka dengan beberapa perlakuan berbeda dan pergerakan free surface-nya. Berdasarkan hasil penelitian dapat disimpulkan bahwa luas free surface memberikan pengaruh terhadap keragaan oleng kapal, dimana semakin luas free surface maka nilai sudut kemiringan, nilai rolling period, dan nilai waktu redam semakin besar, sedangkan untuk nilai frekuensinya semakin mengecil.