As offshore topside continues to become larger and heavier, the float-over method was developed and employed these days as the popular and efficient means for topside installations. Within the float-over method for the topside installation at offshore, passive jacking (rapid load transfer) systems are commonly used in areas with swell wave such as West Africa, India and Myanmar due to high vessel motions.
There is an increasing trend in the use of active jacking system in place of passive system which employs sensor suites to compensate for the vessel motions to ensure minimum clearances during all stages of the float-over operation and improve operational confidence.
This paper outlines the feasibility of active jacking system for float-over operation at the swell wave area based on the model test result in order to compensate the vertical vessel motions during docking operation stages. The model test has been performed using VMG (Virtual Motion Generator) to simulate vessel motion behavior artificially with 4ea of 50M-ton Jacks for 6 M-ton Topside weight and the 3.5-degree angle with 10∼13 second was considered.
The results give some confidence that vessel motions could be compensated vertically by the active jacking system and it is a beneficial test that helps to establish additional test plans better results in the future.
Float-over installation method is normally used for heavy topside structure installations on top of substructure in offshore oil & gas field around the world instead of heavy lifting crane method due to the latter's limited lifting capacities and availabilities.
In the historical trends of float-over installations, the integrated (single) topside weight of offshore structure has been increasing continuously with the heaviest topside at 47,830M-ton installed offshore Sakhalin in the Russian Federation in 2014.
According to the float-over methodology development, hydraulic jacking system for topside installation is considered at swell wave areas such as offshore West Africa, India, Myanmar in order to overcome the challenging operational environments, with prevailing long-period swells that may cause significant motion.