A Study On Ship Turning Ability Under Tugboat Assistance By Using MMG Simulator

This thesis presents a study on ship turning ability under tugboat assistance.The study is directed to assess the behaviour of the turning ability of the ship assisted by tugboats in making a turning manoeuvre,and explore various techniques that tugboats could apply so as to improve the turning ability of the ship.The experimental method was primarily used to collect the quantitative data from the trials conducted,and the documentaries were used to collect the relevant theories and concepts.The trials were carried out by using the MMG model ship-handling simulator which comprises highly standardized techniques of recording the experimental data with a computerized data recorder to collect the numerical data from the trials.The model ship used was a VLCC tanker of 334m LOA and the model tugboats were ASD tugboats with 1800HP,3000HP,4800HP,and 7000HP.The results collected throughout the experiments were summarized,analysed and discussed.The major findings from the experiments in this study revealed that;tugboat assistance has a great impact on the ship turning ability.This impact depends mostly on the assisting tugboat power,the number of assisting tugboats used,the angle of towline from the assisting tugboat to the assisted ship’s hull,the assisting methods applied,and the position of the assisting tugboat against the ship’s side.It is verified that the greater the power of the assisting tugboat,the more the force generated to assist the ship,hence the better the turning ability of the assisted ship.The more the number(quantity)of assisting tugboats applied,the more efficient and powerful the assistance is hence the better the turning ability of the assisted ship.The towline angles of 90 degrees and 75 degrees from the assisting tugboat to the assisted ship’s hull verified to be the best towline angles for improving the turning ability of the ship,however,a towline angle of 60 degrees can be useful.The pushing assisting method against the ship’s hull generates a better turning ability than pulling method.And the best position to place a tugboat against the ship’s side when assisting is from the stern than from the bow.It is concluded that the ship turning ability is improved by tugboat assistance,especially when the tugboat assists by pushing from the ship’s starboard or port quarter.Moreover,the ship turning ability is also improves when assisted by two tugboats with one tugboat pushing at one bow side and the other tugboat pushing at the opposite side of the stern.It is therefore recommended to apply these techniques as they are proved to be the best techniques.Furthermore,if pulling method should be applied,it is recommended to be performed to from the stern of the ship with the towline angles of 90° or 75° from the tugboat to the ship,otherwise to be performed with the preference of using tugboats with different propulsion systems other than azimuthing and conventional propulsion units to minimalize propeller wash effects.Tugboats with their propulsion units at one-third aft of the bow like the tractor type tugboats(Z-drive and Voith-Schneider)are more suggested in pulling,since they are extremely manoeuvrable and powerfully even to pull sideways.Then further studies concerning the topic should be conducted particularly on areas not studied by the researcher.