This paper presents the methodologies and processes used during planning, fabrication and assembly of skidding and loadout systems; and execution of skidding and loadout (at transportation vessel side or stern) of Malikai Tension Leg Platform (Malikai-TLP) and Float-over Topsides as well as comparison between side and stern loadout in terms of constructability, cost, time, operation, equipment and transportation vessel availability.
Malikai-TLP is divided into two (2) major structures namely: Hull (13,000 MT) and Topsides (14,500 MT). Malikai-TLP was loaded-out onto the Host transportation vessel (secured by mooring system) as an integrated structure weighing 27,500 MT using skidding method which consist of skidbeams, active skidshoes and its hydraulic system, outriggers, strand jacks, fixed anchor and stoppers.
The entire loadout operation basically consists of four (4) major activities, namely, jacking-up, break-out and Shore Skidding, cross-over onto the transportation vessel and installation of Lower Sea-fastening.
Spacer barge was inserted in between the Host transportation vessel and the quay wall to prevent the overhanging portion of the structure from clashing onto the quay.
Loadout method used for topside is usually by skidding method using strandjack to pull the topside from fabrication area to transportation vessel. Topside will be sited on top of loadout support frame (LSF) and skidded on skid track. Appropriate skidding medium will be applied on skidway. Strand jack will be attached to LSF and strand wires are laid horizontally from strand jack up to the anchor block supported by dead man anchor (DMA) on transportation vessel. Ballast and deballast activity is required in order transportation vessel in sufficient level during crossover operation.
The Skidding system consists of several structures custom-designed to facilitate the skidding and loadout operation of Malikai-TLP. The skidding operation involves sequential activities such as lifting of the hull, weighing and skidding. Eight additional skid shoes were installed after weighing of TLP to keep the displacement of hull within tolerance. This has to be considered during detailed design stage. Outrigger system reduces operation duration as less ballast is needed because of jack load acting on the transportation vessel. The minimum loadout draft will be preferred due to less ballast utilization for critical steps. Therefore, it is recommended to implement outrigger system for skidding loadout for easier control of transportation vessel trim and list, and the transportation vessel stability will be significantly improved. Introduction of surge stopper on quayside was used to restrain the transportation vessel in the Fore and Aft direction. Skid beam anchoring was placed on the bulkhead to resist uplift force due to tensioning of the strandjack during loadout. Aside from soft mooring lines connected to onshore bollard, additional mooring winch lines is introduced to maintain the positioning of transportation vessel throughout the loadout operation.
The difference between side and stern loadout is the transportation vessel position with respect to quayside during loadout operation. Side loadout is the operation where the position of transportation vessel is parallel to the wharf and longitudinal if it is a stern loadout. The main factor in choosing between these two methods depends on yard capability and transportation vessel availability. Side loadout requires big space in terms of longitudinal area along the wharf for vessel position. Yard needs to have sufficient berthing requirement such as water depth and wharf capacity due to transfer of load. Side loadout is more cost effective than stern loadout since the former has less skidding distance. Conversely, the stern loadout method is safer due to bigger ballast and deballast capacity.
Loadout by skidding is not limited to floatover topside but also to any structure of huge size and weight. It is very important to choose loadout position since it will affect the yard layout giving impact on cost and schedule. Detailed study by considering overall factor is required in order to achieve safe and practical loadout operation.