Estimation of Effective Wave Slope Coefficient of Ships with Large Breadth and Draught Ratio

Abstract

One of parameters to estimate heel angle of a ship in beam seas is effective wave slope coefficient. In the weather criterion of IMO, the effective wave slope coefficient is determined as function of ratio between distance of center of gravity from the sea surface and the ship draught. The others methods could be used to estimate the effective wave slope coefficient are simplified strip theory and model experiment. A ship with shallow draught and large vertical center of gravity can have an effective wave slope coefficient larger than 1.0 if the coefficient is calculated by using the formulae of weather criterion. Therefore, an alternative method to estimate the coefficient is necessary when it is applied to ships with geometry characteristics different with those used to develop the formulae. This research conducts to estimate the effective wave slope coefficient using three different methods, namely the formulae of weather criterion, the simplified strip theory and model experiment. Results of the three methods may provide enough evidence about suitable method to estimate the effective wave slope coefficient of ships with breadth and draught ratio larger than 3.5 like the Indonesian ro-ro ferries. Results and discussion show that the effective wave slope coefficient obtained by using the formulae of weather criterion is larger compared to that obtained by using the simplified strip theory and the model experiment. Here, the result of simplified strip theory for wave frequency the same as the roll natural frequency of subject ship is similar with the result of model experiment. This results show that the simplified strip theory can be used as an alternative method to determine the effective wave slope of a ship with breadth and draught ratio larger than 3.5 if the result of model experiment does not available.

Finding a New Home: Rerouting of Ferry Ships from Merak–Bakauheni to East Indonesian Trajectories

“…This was a combination of data involving the ratio of ship dimensions to wave slope to determine the ships' heel angle. As a correction value, supposing the heel angle of the ferry when sailing was below 25 degrees, it was considered safe [21]. The analysis output showed the ships' suitability to the new trajectories based on three main aspects, usually considered by the stakeholders during policy making.…”

Analysis of empirical method for predicting maneuverability of ultra-large container ship using Maneuvering Modelling Group (MMG) model

“…This approach can simulate the condition of a ship when manoeuvring according to its original requirements but requires quite a large number of resources to complete the simulation. Apart from these methods, other prediction methods are widely used by academics and industry, such as identification systems [7,8,9,10,11] and mathematical models [12,13,14,15] to model ship manoeuvre movements.…”

Hydrodynamics Factors Correspond to the Weather Criterion Applied to an Indonesian Ro-Ro Ferry with Different Weight Distributions

“…To satisfy the capacity requirement, the ships are designed with a large breadth. This requirement results in designs with breadth-todraught ratios of approximately 2.3 to 8.3 (Paroka et al, 2020a). Most of the ships have breadth-to-draught ratios larger than 3.5.…”

“…Indonesian ro-ro ferries have small freeboards to facilitate vehicle loading and unloading at ports. Therefore, the freeboard-to-breadth ratios of most Indonesian ro-ro passenger ferries are smaller than 0.1 (Paroka et al, 2020a). Thus, the heel angle associated with the maximum righting arm is typically smaller than 25° (Paroka, 2018).…”