Research On Flow Rate’s Influence Over The Error Of Draft Survey For Bulk Carriers

Draft survey is a weight method used in weighing bulk commodity by observing the condition of draught, so that getting the ship’s displacement. It is widely used in bulk cargo transport because of the obvious advantages:procedures simple、saving time and high efficiency. With the development of world economy, the large-scale trends of bulk carrier, and the rising value of cargo, the accuracy requirement of draft survey is higher and higher. It is important to add necessary correction and reduce error in order to improve the accuracy.This thesis has a systematic analysis on the error of draft survey based on logic tree method, which leads to26kinds of error sources. According to their different characteristics, the author puts forward different correcting ways. In addition, the author also finds one systematic error cannot be fixed by regular operational approaches, which results in the six draft readings always higher than the actual value.The author comes to a conclusion that the appearance of ship squat is because of the relative movement between ship and water. Through the differential of calculating formula, the author obtains the data of transfer coefficient based on error delivering theory. Thereby, the ship squat’s influence on final calculating result can be judged by the superposition of errors. The ship squat error has a huge influence on the draft survey result, which cannot be ignored in calculating.In order to correct the error, the author chooses five formulas to estimate deflection and makes comparison among five measured data from three bulk carriers in different tonners (50,000tons,100,000tons, and150,000tons). The Barrass formula is used in calculating the squat by flow rate, and involved in draft survey method. After example verifications, the Barrass formula can not only correct the squat error effectively, but also simple to handle on obtaining data. This research achievement improves draft survey method on bulk carrier, consequently increases the accuracy of draft survey.