Offshore Loading and Discharge in Heavy Marine Transport

Abstract

Dry transporting large heavy floating structures has been an important development in the innovative history of Heavy Marine Transport. This is done by carrying these type of cargoes on the deck of Heavy Transport Vessels. Loading and discharge is preformed by submerging the transport vessel, and positioning the cargo above the deck using tugger winches. Traditionally, these operations take place in sheltered locations, like harbours, where virtually no waves occur. From the beginning Heavy Marine Transport has served the oil and gas industry in the exploration, development and production phase of offshore oil and gas fields. In search of optimizing profitability of remote offshore fields, optimizing fabrication and installation of facilities is essential. Delivering the facilities directly at the remote fields is recognized as a potential cost saving. Also, Inspection, Maintenance and Repair by offshore dry-docking is a potential cost optimisation. Both imply that loading and discharge operations need to be carried out in exposed areas, where wave conditions do occur. It is evident that, to ensure acceptable workability and safe operation, it is important to accurately prediction the dynamic motions and to assess and design the mooring and handling equipment. Experience and model testing has shown that prediction of vertical relative motions using industry standard software was inaccurate; generally, the relative vertical motions were significantly over-predicted. Also, it has been shown that horizontal relative motions are too large to safely place the cargo on cribbing support, while using the standard handling equipment. These issues have resulted in the development of an accurate method to predict relative vertical motions and the development of cargo handling equipment for accurate positioning of the cargo.