Abstract
Existing methods presented in references and standards for calculation of berth occupancy ratio, are more concentrated on container terminals. However, some empirical formulas can be found to predict the berth occupancy, but these methods are neither accurate enough nor economically wise to be employed for the prediction of berth occupancy ratio in large and complex bulk liquid terminals. Therefore, it is attempted in this paper to introduce a method for more precise prediction of berth occupancy ratio for bulk liquid terminals. In the proposed method for calculation of berth occupancy ratio in bulk liquid terminals, times which is not used for loading/unloading operation is investigated. The loading/unloading lost factor is considered in calculations in order to calculate the operational value for loading/unloading rate. Next, practical values for these items are given based on previous authors' experiences. Finally, a case study is performed for a liquid bulk petrochemical terminal to specify the presented method. Results show 24% difference between new method and old empirical formulas.
Introduction
Occupancy ratio plays an important role in port planning and port master plan design. The number of berths should be established based on operational requirements, driven primarily by berth occupancy considerations. The optimum berth occupancy depends on throughput requirements and site constraints. The assessment of the berth occupancy is based on the consideration of vessel arrival and departure times, time at berth or vessel turnaround time, downtime caused by maintenance, and severe environmental conditions (stopping of loading and/or vessel leaving the berth) (1) . Vessel turnaround time is the duration of vessel's stay afloat alongside berth and also viewed as port's operational indicator for its optimum performance in term of the capability, efficiency, and productivity of operation processes of petroleum terminal in handling inbound and outbound cargoes via public liquid-bulk jetties (2). Estimation of vessel (or container group per ship) turnaround time during the considered time period depends on the acceptable average waiting time to average service time ratio. This parameter is obtained as the function of berth occupancy, number of berths, number of containers, waiting and service times and berthing and unberthing times (3).
Introduction
Various methods and approaches are presented in references and standards for definition of berth occupancy ratio. For example, this ratio is presented in PIANC mainly in term of yearly working times that results an average value of occupancy ratio in a year (4) . Carl A. Thoresen, 2003 (5) defines this ratio in term of weekly working and service hours which may results various values for seasons and every month in a year. In addition to design stage and port planning, occupancy ratio is used to evaluate in service port performance in order to planning and performance optimization purpose. Berth occupancy studies help the designers to plan a terminal in optimum throughput, traffic condition and ship waiting time. Low value of berth occupancy ratio is not acceptable to the port authority from economically point of view, while the high value lead to traffic congestion and increase of ship waiting time. The optimum range of 30-90 (4) and 40-70 (6) percent are given in terms of number of berth and cargo type (container, bulk and liquid bulk) in the related standards.
Introduction
Generally, berth occupancy ratio shows the port service level which can be defined as bellow: In case of investigation of berth occupancy ratio in actual operational condition (previous port performance), o T may be calculated based on registered times in ships' statement of fact documents for the proposed timespan which is calculated as below for each berth separately:
Introduction
The registered time in ship's statement of fact do cuments that ship is unberthed from the quay (hour). Total number of ship which is berthed in the proposed berth for the proposed time span.
Introduction
In case of investigating berth occupancy ratio for port planning, The ratio of port yearly throughput to port loading/unloading capacity results an estimate for o T (equation 3). T is investigated in two parts. First, times for loading/unloading operation and second, times for tank inspection and sampling, documentation and clearance. As performance system and timing are different for container, dry bulk and bulk liquid terminals, calculation of o T is presented for each terminal separately.
Container Terminals
The investigation of container terminals in respect to BOR is completely different with other terminals and mainly affected by productivity of each meter of quay wall length, which is estimated by crane density in quay wall and crane productivity. These numbers vary in term of berth design vessel and loading/unloading equipment. The average value of crane density is one crane per 100 m of quay wall and in modern container terminals is about one crane per 75 m. The crane productivity varies from 10 lift/hour for mobile harbor cranes to 30 lift/hour for modern ship to shore gantry cranes (4) . So, o T in container terminals can be calculated as presented in below equation: other T Times which are related to inspections, documentation and clearance in hour which should be calculated based on port performance.
Dry Bulk Terminals
As cargo type and loading/unloading capacity of equipment may vary in each berth of a bulk terminal (liquid/dry), the occupancy ratio calculation for these ports should be investigated for each berth or berths with the same cargo type and loading/unloading equipment separately. So, the relation for o T is given as below in term of annual throughput and number of ship in year: 
Bulk Liquid Terminals
The formula for bulk liquid terminals is like dry bulk terminals but product density and loading/unloading lost factor should be considered in calculations. So, the equation 5 is rewritten as below: In bulk liquid terminals the operational value for berth's equipment productivity is not the same 
Sirous Zamanirad et. Al. / Introducing a Method for More Precise Prediction of Berth Occupancy Ratio in Bulk Liquid Terminals
nominal values mainly due to product evaporation (for liquid gas products), pump performance and due to line blowing after loading completion. So, the loading/unloading lost factor is applied here for more exact results. The below equation is given to calculate lost factor for each product or product with the same specification: The value of lost factor is various for liquid and gas products and ever may changes for various products by density. Product handling in bulk liquid terminal with high value of annual throughput like oil terminals is performed by more than one loading arm or hose. In this case, the total value of equipment productivity ( 
BOR
Reefer to equation 1 .
BOR
Reefer to equation 9
BOR
Parameters like loading/unloading lost factor and times which are not usable for loading/unloading operation have been applied in equation 3 to reach more exact results for o T . It is clear that berth occupancy ratio is generally affected by berth's equipment productivity and terminal working hours, but the presented parameters may change the result considerably. To clarify the difference of results for each method, In the next section a case study is performed for calculation of berth occupancy ratio in a bulk liquid petrochemical terminal.
Case Study-Occupancy Ratio in a Bulk liquid terminal
In this section, a case study has been performed in one berth of a petrochemical terminal. The proposed berth performs loading/unloading of 9 product with 8 loading/unloading equipment as shown in Figure 2 . Before investigation of berth occupancy ratio in a terminal, it is necessary to analyze ship's times in the port from arriving to leaving. Details of these times are presented in Figure 1 , should be specified for the proposed investigated port. It could be more applicable if the breakdown be studied along with port performance process diagram. The port performance process diagram for the proposed port is presented in Figure 3 . Port performance process diagram directly affects berth occupancy ratio and shall be analyzed before berth occupancy ratio calculation. In some cases, optimization in this diagram may reduce berth occupancy ratio. For example, in some bulk liquid terminals, pre-loading tank inspections are performed in berth which increases ship's times at berth and berth occupancy ratio. But in the investigated port these tests are performed in harbor (pre-berth times) that reduces ship's times at berth and berth occupancy ratio. Parts which are related to ship's at berth times are separated in The port performance process diagram (Figure 3) .
Case Study-Occupancy Ratio in a Bulk liquid terminal
The yearly throughput of each product is shown in the considered for loading/unloading lost factor in the investigated berth. As given in the last row of table 1, the berth was occupied for 5,838 hours in a year. Considering 365 working days in a year and 24 working hours in a day, t T is 8760 hours for this berth (for a year). So, the occupancy ratio for the berth is 67% based on equation 1. In the last column total time which quay walls are occupied ( o T ) was given with the general equation for calculation of this number (equation 3) and the value of 43% was calculated for occupancy ratio which has about 24% difference with the new proposed method.
Conclusion
Calculation of berth occupancy ratio are investigated for container, dry bulk and bulk liquid terminals in present study. Considering various parameter in bulk liquid terminals, a method for more precise prediction of berth occupancy ratio has been introduced for these terminals. However, berth occupancy ratio is generally affected by berth's equipment productivity and terminal working hours, other factors like loading/unloading lost factor and times which are not usable for loading/unloading should be considered in bulk liquid terminals. Finally, to clarify the proposed method, a case study was performed in a bulk liquid terminal. The impact of 24% was observed for considering of loading/unloading lost factor and times which are not usable for loading/unloading in calculation of berth occupancy ratio for the terminal.

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