The floating harbour transhipper: hydrodynamic considerations for well docks

The floating harbour transhipper (FHT) aims to improve the efficiency and cost effectiveness of transhipment operations using a mothership with an aft well dock, however this can introduce complex confined water effects. This paper summarises an experimental investigation of the hydrodynamics surrounding a feeder vessel operating within a well dock. Well dock vents are hypothesised to minimise negative confined water effects, possibly at the expense of reducing the sheltering effect. The effect that the vents have on several operational aspects of the concept are explored, particularly as the feeder vessel enters and exits the well dock of a mothership.

Initially, the seakeeping performance of the feeder vessel in open water was compared against that when docked within the mothership’s well dock. The feeder vessel motions were unsurprisingly found to be significantly reduced because the well dock provides shelter, which should provide a notably increased operational weather window. The size of vents was found to influence the motions of the docked feeder vessel.

The next stage investigated the effect that the confined space of the well dock had on the behaviour of the feeder vessel as it enters and exits the well dock, compared to operation in more typical open water environments. Conventional measurements of resistance, trim and sinkage were employed along with more advanced methods including laser diagnostic techniques to analyse the complex flow fields present as a result of this somewhat unique shipping operation. This combination of measurements significantly increased understanding of the unique conditions posed by the well dock operations and the mitigating and control offered by introducing the vents.

Observations indicate that vents provide significant advantages, however appropriate sizing is important to achieve a balance between the advantages gained when the feeder vessel enters/exits the well dock and any potential reduction in sheltering effect when in a seaway.