ABSTRACT

This paper reviews recent progress in the field of offshore bulk terminals. The economy and practicability of large ships, of rapid loading and unloading, and of large yearly through puts is established.

The trend toward building open sea berths at increasingly exposed locations requires sophisticated techniques, such as the determination and analysis of wave spectra. The SEABERTH computer program and its utilization in the planning and design of mooring systems is described, together with hydraulic model tests to verify the results of the computer analysis. Berth availability criteria are discussed as function of wave height, wave period, ship size, and mooring system characteristics.

Specific examples are used to demonstrate the utilization of the accumulated knowledge: the Ponta Dobela, Mozambique, multiproduct terminal berthing 350,000-dwt ships exposed to heavy swell; the Punta Colorada, Argentina, offshore berth with variable ship orientation; the Areia Branca-artificial island terminal located 15 km from shore; and the Santa Clara, Gabon, shiploading terminal connected to shore by a 7-km long approach structure.

INTRODUCTION

Considerable progress has been made during the last 5 years in the design and construction of offshore bulk terminals. These specialized terminals were developed to load and unload -large ocean-going bulk carriers at locations where suitable deep-sea harbors are not available.

Before the 1970' s, the development or Offshore bulk terminals proceeded together with that of tanker terminals built for the handling of crude oil, petroleum products and other liquid bulk cargoes. However, the development of single-point mooring (SPM) systems offered a practical method for the handling of liquid cargoes in the open sea; and most progress in that field concentrated on further improvements to SPM systems.

Since dry bulk cargoes cannot be handled with SPM's, but require fixed berths, these required further development to keep up with the trend toward larger bulk carriers, higher shiploading rates, more exposed locations and larger yearly volumes. Such development took place at a rapid pace in a relatively short time.

DEVELOPMENT OF OFFSHORE TERMINALS

The first offshore bulk terminals were built close to the open coast, or in partially protected waters (Fig. 1) and employed conventional bulk handling equipment to load and unload relatively small ships. The yearly volumes handled were modest and, with ships arriving several days apart, there was sufficient time to make up for any delays caused by unfavorable sea conditions.

During the 1960' s, offshore terminals were constructed up to a mile from shore, in exposed locations in waters deep enough for 120,000dwt ore carriers (Fig. 2). In planning the open-sea berths, great emphasis was placed on the orientation of berthed ships in relation to the direction of winds, waves and currents. Measures were taken to increase berth availability, i. e., the number of days per year when ships can dock and loading or unloading can proceed.

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