Reduction of green house gas from international shipping shall be put forward. For the reduction, it is important to promote to introduce ships of high energy efficiency to the shipping market. In actual seas a ship decreases her speed not only the deterioration and fouling effect but also by natural forces such as winds and waves. By design technique, ship propulsive performance in actual seas is able to improve. Hence ship propulsive performance in actual seas has much scope to improve the energy efficiency.We present a calculation method of decrease of ship speed in actual seas. From the point of accuracy, the method involves correction for added resistance in short waves combined with a tank test. As examples three kind of ship; a container ship, a car carrier and a bulk carrier are examined and the components of external forces acting on the ship are discussed.
Greenhouse gas shall be reduced from shipping sector. For that purpose the regulation of EEDI (energy efficiency design index for new ships) and SEEMP (ship energy efficiency management plan) have been entry into force from 2013. In order to improve the energy efficiency in ship operation it is necessary to predict the fuel consumption accurately. In actual seas the wave effect is the dominant component of the external forces. In particular it is well known the bow shape above water affects the added resistance in waves. To reflect the effect of the bow shape a method which takes into account the result of simplified tank tests is proposed here. Using the results of tank tests the effect of the bow shape above water can be evaluated with accuracy as well as with robustness. Regarding to the fuel consumption it should be evaluated by combining the ship hydrodynamic performance with the engine characteristics. Especially the operating limits of the main engine, such as the torque limit and the over load protection, are affected to the ship hydrodynamic performance. In rough weather condition the revolution of the main engine will be reduced to be below the operating limits of the engine. This causes the large decrease of ship speed. To prevent the increase of fuel consumption, a control system by Fuel Index as an index of fuel injection has been applied to some ships. The calculation method for the fuel consumption by using Fuel Index is presented. In this paper following contents are reported; 1) development of a calculation method for the added resistance due to waves combined with the simplified tank tests in short waves, 2) comparison of the calculation method with onboard measurement, 3) development of a calculation method for the fuel consumption considering the engine operating mode in actual seas and 4) comparison of the method with onboard measurement of a container ship. From these investigations the availability of the present method is confirmed.
On prediction of ship performance in actual seas, it is important to estimate external forces acting on a ship. The predominant factor is added resistance in waves which reduces ship speed. Therefore, added resistance in waves is required to be calculated with accuracy. In addition, since a ship sails with a drift motion due to winds and waves, it is required to estimate hydrodynamic forces and moment due to drift motion. As ocean waves is characterized their irregularity which contains various frequency and direction component, it is required to estimate added resistance in oblique waves as well as in heading waves. In this paper, it is investigated by tank tests whether the calculation method on added resistance in heading waves is applied to that in oblique waves. Furthermore, hydrodynamic forces and moment due to drift motion is calculated with appending a term of drag for wing of a small aspect ratio. The effectiveness of the calculation methods is shown by estimating decrease of ship speed in actual seas.
Estimation of ship speed in actual seas is very important to evaluate the comprehensive performance in her life. Estimation of the added resistance in ballast condition is more difficult than that in full load condition due to the complicated phenomena around the bulbous bow. The proposed method, which combines tank tests with calculation, shows the estimation of added resistance in ballast condition accurate for a Panamax bulk carrier. In this paper, the proposed method is applied to a handy-size bulk carrier (approximately 160m length) equipped with cranes in both ballast and full load conditions, and its accuracy is confirmed by model tests and onboard measurements. Moreover the difference of resistance components due to winds and waves is discussed in terms of load condition toward the improvement of evaluation of performance in actual seas for handy-size bulk carriers equipped with cranes.
Evaluations of ship performance in actual seas based on onboard monitoring data have been widely conducted recently. Performance in a calm sea is important for estimating performance in actual seas. In order to estimate performance in a calm sea, onboard monitoring data should be filtered by certain items and criteria. This filtering procedure is important and difficult because the data depend on the filtering items and criteria, and the appropriate items and criteria will be different depending on the ambient condition and ship size. To solve this problem, this paper proposes a filtering method called the Resistance Criteria Method (RCM) using the estimated added resistance in actual seas. The method was validated with a tanker (VLCC) and compared with other filtering methods.
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