Determination of an Optimal Fleet for a CNG Transportation Scenario in the Mediterranean Sea

Abstract

For the natural gas transportation, several technologies can be applied, having different effectiveness and costs depending on the analysed case. The Mediterranean Sea is presenting a typical scenario where compressed natural gas (CNG) transportation is particularly attractive compared to liquefied natural gas (LNG) and pipelines, not only for stranded gas shipping but also for transportations cases where CNG is usually representing the most economically convenient solution. Approaching the design of a CNG ship is not an easy task, since the pressure vessel (PV) technology is strongly influencing the ship layout and hull form. Here an enhanced conceptual design method is adopted; taking into account the economic-financial issues together with logistics, in order to determine the best fleet composition selecting the best ships for the selected scenario. The ships composing the fleet are supposed to load/offload the natural gas on buoys; hence, dynamic positioning (DP) will also be considered as an attribute in the evaluation of alternative designs. As final outcome of the enhanced concept design process it will be possible to speed up drawing of the preliminary lines plan and general arrangement plan of the sister ships composing the fleet.

LCTC Ships Concept Design in the North Europe- Mediterranean Transport Scenario Focusing on Intact Stability Issues

“…Thus, in Valencia (17), the last Mediterranean stop, a significant percentage of vehicles can be loaded. In Setubal (18) there is a substantial equilibrium of loaded and unloaded vehicles. Then, the ship is involved in the short portto-port [11] Portbury (19)-Cork (20)-Portbury (21).…”

“…A detailed explanation of all the modules of MDM (Figure 2) goes beyond the purpose of the present paper, which focuses only on stability issues. Nevertheless, more details can be found in previous literature, such as [3][4][5]13,[15][16][17][18]. Since the primary task of concept design is to find the ship size for required performance and payload as well as for the valuation of ship's total cost, it is usual practice to include most of the ship linear dimensions and main coefficients in the set of free design variables of the MDM.…”

A Model for Intact and Damage Stability Evaluation of CNG Ships during the Concept Design Stage

“…As mentioned, the technologies used for the PV influence greatly the CNG ship design. Modern technologies combining composites and steel structures or using composite only, allow reducing the weight of the containment system, leading to more slender hull forms compared to first CNG ship prototypes [12]. Another distinctive characteristic of CNG units is the presence of a flat bottom part in the bow to allow the connection of the submerged turret loading (STL) for the gas loading operation [13].…”

“…All the variables vary between a minimum and a maximum, as reported in Table 2. The ranges were selected based on of previous studies [11][12][13][14], where specific ranges of geometrical coefficients were identified for the development of other metamodels (e.g., seakeeping, station-keeping, propulsion and internal layout). To maintain compliance with the other models, the same ranges were applied for the common variables.…”

“…As first, the effective floodable lengths FL were determined dividing the GFL by the permeabilities µ reported in Table 12. According to the authors of [12,13], the main dimensions of aft and fore compartments were defined considering the propulsion system and the STL system. Comparing the length of compartments with the floodable lengths, the subdivision in these regions was found feasible.…”