Investigation of the Mighty Servant 3 Accident by a Progressive Flooding Method

Abstract

The semi-submersible heavy-lift vessel Mighty Servant 3 sank off the port of Luanda, Angola in the morning of December 6th, 2006 during a ballast operation to offload the drilling platform Aleutian Key. The official investigations carried out after the accident identified an error in the control of the submerging ballast operations as the direct cause of the sinking. However, the detailed phenomenons and reasons for the sudden excessive trim development has not been investigated further. This paper intends to identify the most likely sceneario which lead to the hydrostatic stability failure during the discharge operation by computing the flooding process during the ballast operation in the time domain. A numerical progressive flooding simulation method is presented for applications like accident investigations or damage stability assessments. This method is modified to fit the special requirements of simulating the operational procedures of semi-submersible vessels in the time domain. Extensions like the inclusion of pump elements but also the multi-body interaction of the cargo and the vessel with regard to the hydrostatics is presented. The direct flooding simulation computes the flux between the compartments based on the Bernoulli equation and the current pressure heads at each intermediate step. Large and partly flooded holes are taken into account as well as optional air compression and flooding through completely filled rooms. Pressure losses due to viscous effects are taken into account by applying semi-empirical discharge coefficients to each opening. The flooding paths are modeled by directed graphs. A detailed investigation of the Mighty Servant 3 accident and an identification of the possible failure modes leading to the sinking of the vessel is presented. This will help to better understand the phenomenons leading to critical situations during the submerging procedure of semi-submersible heavy-lift vessels and to avoid such accidents in the future. Applying time domain flooding simulations allows to predict the ship behavior during ballast operations to identify critical situations and to better schedule the different steps of such an operation in advance.

Calculation of the Hydrostatic and Structural Integrity of Docking Sequences

“…The applied flooding simulation method has initially been developed to investigate real scale ship accidents. An elaborate description of the computational and the theoretical background can be found in the thesis (Dankowski, 2013) together with its validation with experiments.…”

“…This method has already been successfully applied to investigate the deballasting of a semi-submersible vessel to unload its cargo as described in (Dankowski, et al, 2013). In this paper the described kind of application is further extended to be coupled with structural computations of the involved floating bodies.…”

New Insights Into the Flooding Sequence of the Costa Concordia Accident

“…More details about additional features like the influence of a contact with the sea bottom can be found for example in [4,2].…”

Study on submerging operation design for heavy-lift barges based on a real case analysis

“…During a float-off operation that took place on 6 December 2006 near the port of Luanda, Angola, Mighty Servant 3 (a semi-submersible vessel) exceeded its design limit and eventually sank to the seabed. 2 Another accident happened on 18 July 2014 in which a semi-submersible barge named ''POSH Mogami'' sank near the northeast of Skeupang, Batam, during a submerging trial. 3 According to the crew, only the repaired part of the vessel was submerged for testing.…”

“…Therefore, a well-designed flooding sequence is crucial for the success of submerging operations. There have been limited publications on the analysis and design of flooding sequences, 2,5,6 and this field has not been thoroughly studied yet.…”