Push-Towed Ocean Going Tug-Barge Operation in the Integral and Drop-and- Swap Modes: An Economic Comparison Using a Computer Model

摘要

Currently, all large ocean-going, mechanically linked tug-barge units are being operated in the integral or ship like mode where the tug and barge remain together at all times. This method of operation does not take advantage of the inherent flexibility available to tug-barge units--the ability to separate the propulsive unit (tug) from the cargo unit (barge). This separability can be used to operate the tugs and barges in a drop-and-swap mode where the tug drops off a loaded barge at a port and then swaps it for one that has completed its cargo operations. This method substantially increases tug utilization since the tug is not required to await cargo operations. However, this increased tug utilization is achieved at the expense of the extra barge units which remain in port for cargo operations. The question is whether in drop-and-swap operation the increased tug utilization outweighs the capital costs of the additional barges. To help answer this question, a computer model is developed to compare the total capital and operating cost of providing transport capacity for simple port pair trades with tugs and barges operated in the integral and drop-and-swap mode. From the model's output it can be determined which mode is more economical for a given trade. The model uses exhaustive enumeration to select among all feasible alternatives the number of tugs and barges, the barge size and form, and the tug-barge system speed that provides the desired transport capacity for a given port pair trade at the lowest required freight rate. The required freight rate calculation takes in account the tug, barge storage tank, and terminal facility annual operating and annualized capital costs. Most of the capital and operating cost elements are obtained from the literature. However practically no data are available for two of the most important cost factors, barge capital cons.