The weather criterion is one of stability criteria to verify ability of a ships to withstand the combined effects of severe wind and rolling criteria in dead ship condition. An overestimated roll angle is obtained when the weather criterion is applied to ships with breadth and draught ratios larger than 3.50 and ratios between vertical centre of gravity and draught larger than 1.50. This paper discusses the assessment of weather criterion for an Indonesian ro-ro ferry by model experiments. The drift test is performed in four wave steepnesses with wave frequencies near the roll natural frequency. The maximum roll amplitude is used to calculate the effective wave slope coefficient corresponding to the wave steepness, with Bertin’s coefficient obtained by the roll decay test. The damping factors correspond to the breadth and draught ratio as well as the bilge keel contribution are determined using the formula of weather criterion with the roll angle obtained by the Japanese formula with a correction factor of 0.70 due to the irregularity of waves. The obtained effective wave slope coefficient and the damping factors due to breadth and draught ratio and the bilge keel are smaller than those used in the weather criterion.

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Wind force and moment may force a ship to drastically decrease its speed and use a large drift angle as well as a large rudder angle in order to maintain its course. Ships with a small draught might have more risk in maneuvering to its point of view compared with a ship with a larger draught. This paper discusses maneuverability of a ship with a small draught in steady wind. The effect of wind on ship speed, drift angle, and rudder angle are investigated in a steady state condition. Five different ratios of wind velocity to ship speed from 1.0 to 20.0 are used in the simulation. The variation in wind direction is examined from 0° to 180°. Results of the numerical simulation show that the wind has a significant effect on the reduction in ship speed with a wind direction less than 100°. The drift angle increases due to increasing wind velocity in the same wind direction. Wind direction also has a significant effect on the drift angle especially when the wind direction is less than 140°. The same phenomenon was found for the rudder angle. The necessary rudder angle is greater than the maximum rudder angle of the ship when the wind direction is 60° with a wind velocity to ship speed ratio of 20 or more. AbstrakKemampuan Manuver Kapal dengan Sarat Kecil pada Kecepatan Angin Konstan. Gaya dan momen yang ditimbulkan oleh angin dapat mengakibatkan kecepatan operasi kapal berkurang secara drastis, sudut geser yang besar serta sudut kemudi yang besar untuk mempertahankan arah gerak kapal. Kapal dengan sarat yang kecil mempunyai kemungkinan yang lebih besar untuk mengalami masalah manuvering tersebut dibandingkan dengan kapal dengan sarat yang besar. Tulisan ini membahas performa manuvering kapal dengan sarat kecil pada kondisi angin dengan kecepatan konstan. Lima perbandingan kecepatan angin dan kecepatan kapal tersebut, yaitu 1,0, 5,0, 10,0, 15,0 dan 20,0 digunakan untuk simulasi. Arah data angin terhadap kapal divariasikan mulai dari 0° sampai 180°. Sudut geser kapal bertambah besar dengan bertambahnya kecepatan angin. Arah angin juga mempunyai pengaruh yang signifikan terhadap sudut geser khususnya pada sudut datang angin lebih kecil dari 140°. Fenomena yang sama terjadi pada kasus sudut kemudi. Sudut kemudi yang diperlukan untuk mempertahankan arah gerak kapal maksimum terjadi pada sudut datang angin 60° untuk perbandingan kecepatan angin dan kecepatan kapal (v/c) sama dengan atau lebih besar dari 20.0.

Maneuverability is important in ship design stage not only for ship performance but also for safety reason regarding the collision and stability especially in quartering following waves. The International Maritime Organization (IMO) therefore developed maneuvering criteria and collision regulation to ensure the ship safety against collision. This paper discusses maneuvering performance of ship under combined action of wind and wave. The steady state equations of ship maneuvering were numerically solved using the Newton-Rhapson method in order to obtain the drift angle, the rudder angle and the ship forward speed. Results of numerical simulations show that the combined action of wind and wave has significant effect on the drift angle and the rudder angle in the range of wind and wave direction between 20.0 degrees and 120.0 degrees. The ship forward speed significantly changes due to alteration of wind velocity in the wind and wave direction smaller than 40.0 degrees or in the wind and wave direction larger than 140.0 degrees. The wave height has significant effect on the ship forward speed in the wind and wave direction between 20.0 degrees and 80.0 degrees.

Wind force and moment may force a ship to drastically decrease its speed and use a large drift angle as well as a large rudder angle in order to maintain its course. Ships with a small draught might have more risk in maneuvering to its point of view compared with a ship with a larger draught. This paper discusses maneuverability of a ship with a small draught in steady wind. The effect of wind on ship speed, drift angle, and rudder angle are investigated in a steady state condition. Five different ratios of wind velocity to ship speed from 1.0 to 20.0 are used in the simulation. The variation in wind direction is examined from 0° to 180°. Results of the numerical simulation show that the wind has a significant effect on the reduction in ship speed with a wind direction less than 100°. The drift angle increases due to increasing wind velocity in the same wind direction. Wind direction also has a significant effect on the drift angle especially when the wind direction is less than 140°. The same phenomenon was found for the rudder angle. The necessary rudder angle is greater than the maximum rudder angle of the ship when the wind direction is 60° with a wind velocity to ship speed ratio of 20 or more. AbstrakKemampuan Manuver Kapal dengan Sarat Kecil pada Kecepatan Angin Konstan. Gaya dan momen yang ditimbulkan oleh angin dapat mengakibatkan kecepatan operasi kapal berkurang secara drastis, sudut geser yang besar serta sudut kemudi yang besar untuk mempertahankan arah gerak kapal. Kapal dengan sarat yang kecil mempunyai kemungkinan yang lebih besar untuk mengalami masalah manuvering tersebut dibandingkan dengan kapal dengan sarat yang besar. Tulisan ini membahas performa manuvering kapal dengan sarat kecil pada kondisi angin dengan kecepatan konstan. Lima perbandingan kecepatan angin dan kecepatan kapal tersebut, yaitu 1,0, 5,0, 10,0, 15,0 dan 20,0 digunakan untuk simulasi. Arah data angin terhadap kapal divariasikan mulai dari 0° sampai 180°. Sudut geser kapal bertambah besar dengan bertambahnya kecepatan angin. Arah angin juga mempunyai pengaruh yang signifikan terhadap sudut geser khususnya pada sudut datang angin lebih kecil dari 140°. Fenomena yang sama terjadi pada kasus sudut kemudi. Sudut kemudi yang diperlukan untuk mempertahankan arah gerak kapal maksimum terjadi pada sudut datang angin 60° untuk perbandingan kecepatan angin dan kecepatan kapal (v/c) sama dengan atau lebih besar dari 20.0.