Meeting Your Customized Natural Gas Supply and Delivery Needs

EnerSea offers its marine CNG delivery service to clients based on their specific needs. The VOTRANS™ marine gas delivery service can be provided through fit-for-purpose ships or barges which are tailored to meet the project’s needs. EnerSea’s technology provides the ability to move as much as 1 Bcf or as little as 20 MMscf per vessel, at significantly lower costs than other gas export alternatives.The selection of ship type is dependent on several factors with the most significant factors being:

  • Rate and volume of gas to be transported
  • Distance to market
  • Sea conditions
  • Offshore/onshore terminals

Additional Info

Vessel design drivers

  • Delivery rate
  • Distance from supply to market
  • Offshore/onshore terminals
  • Sea conditions
Vessel Gas Capacity 20-100 MMscf 70-1000 MMscf
Daily Deliverability 7-100 MMscf/d 50-300+ MMscf/d
Economic Range 50-750 nm 250-2500 nm

CNG offers clients great flexibility to meet gas supply and delivery objectives. For example, loading and offloading terminal facilities can be located at traditional port jetties at or near shore. If gas supply is offshore, buoys can be utilized. Gas compression and cooling can be located either at the client’s production facilities or onboard EnerSea’s vessels or, if onshore, at port. Offloading facilities can be located either at port or on EnerSea’s vessels, if offloading offshore.

EnerSea can also provide VOLANDS (Volume Optimized Land Storage), an innovative, above-ground compressed natural gas land-based storage system. VOLANDS can be integrated into a marine gas transport project, or can be provided as a stand-alone storage solution for clients in geologically constrained areas worldwide.



The heart of EnerSea’s ship-based marine gas transport service is its VOTRANS™ gas carrier. EnerSea has developed preliminary designs for ships with natural gas capacities ranging from 70 million cubic feet (2 million cubic meters) up to 1 billion cubic feet (30 million cubic meters) to provide clients with an optimum gas delivery solution. These vessels may be further tailored to confidently meet a project’s unique and demanding field requirements, such as capacity, supply conditions, gas composition, sea conditions and loading and offloading rates. These project specific requirements are normally defined in enough detail during FEED (Front-end Engineering and Design) to allow EnerSea to develop detailed ship designs. A typical VOTRANS CNG ship General Arrangement is shown.

EnerSea’s CNG cargo containment system consists of an array of storage cylinders configured into multiple tanks (several cylinders manifolded together in a common pressure environment and controlled by the same valving) and tiers (two or more tanks configured to load and offload together). The numbers of cylinders, tanks and tiers are dependent on vessel carrying capacity and loading and offloading durations. The storage cylinders will typically reside in multiple insulated cargo holds, the number of which is determined by the overall ship capacity. The holds are inerted with dry nitrogen and equipped with refrigeration coils located at the top of each hold to offset environmental heat gain and thus preserve the internal temperature at 30°C (-22°F). This arrangement is inherently scalable and provides segregated gas storage.

Ship close-up

The cylinders will be manufactured using 48” dia. high strength micro-alloy carbon steel with low temperature toughness and having a wall thickness that ranges from 22 to 25mm. The cylinders will be capped with semi-elliptical heads on each end. EnerSea has qualified pipe materials from Nippon Steel Corporation, JFE and Sumitomo during its Prototype Test Program, the results of which were approved by ABS and DNV-GL.

The vessel has been designed to the ABS Guide for Vessels Intended to Carry Compressed Natural Gases in Bulk for structure and marine systems while the cargo containment system has been designed using API, ABS and IGC codes where applicable. The cargo loading and offloading systems have been designed to comply with ABS, IMO, API and other rules as applicable.

The ship’s lightship draft is designed to ensure that the vessel can be constructed and the cargo containment system installed entirely in dry dock. More importantly, this also allows the vessel to be dry docked in numerous ports worldwide for servicing and maintenance.

EnerSea has worked closely with globally recognized ship operators, shipyards and engineering and naval architecture firms in the development of the vessel designs, ship specifications and ship operating and maintenance plans.


Barge-based Natural Gas Transport & Delivery Services


EnerSea can provide a barge-based CNG delivery service for the needs of smaller markets, such as electrical utilities in remote coastal and island sites using costly fuel oil and diesel. To provide a more cost-effective and fit-for-purpose solution for these markets, EnerSea’s barge-based CNG delivery systems have been developed on the same VOTRANS™ technology and principles used in its industry-leading ship-based system.

EnerSea’s CNG barge system provides solutions for gas delivery needs in the range of <10 MMscfd to over 100 MMscfd over transit distances ranging from 50 to 75 miles.

The gas handling facilities for the barge-based system will be located at the port area rather than aboard the vessel to minimize cost and marine manpower. The barges will operate in shuttle fashion, thereby also acting as storage during ratable loading and unloading operations.

The barge-based system can employ an articulated tug-barge design (ATB) if required, dependent on speed and sea conditions, wherein the tug is coupled directly to the barge. The ATB will provide for better speed, efficiency and maneuverability in the open seas than towed barges, which results in a low-cost service.

The CNG barges can be constructed in numerous yards worldwide, providing greater flexibility for project timing and cost competitiveness than for large-scale ship constructions. CNG barge projects can be placed into operation in approximately two years from project sanction.

ABS has confirmed that EnerSea’s CNG barge design is within the Approval in Principle certification that was granted to EnerSea’s VOTRANS CNG ship system.

Natural Gas Terminals

CNG Terminal Design


Requirements such as location (offshore or at-shore), land availability and environmental factors will dictate EnerSea’s recommendation for the CNG terminal design. Articulated arms for CNG cargo transfer are proven in operation worldwide and can be used for at-shore loading/unloading terminals.

CNG buoys are also proven in operation worldwide that can be used for offshore loading/unloading terminals.

EnerSea has qualified a number of CNG cargo transfer applications, as follows:

  • Loading arms for port solutions (Emco Wheaton Hi-pressure arms)
  • SALM (Single-Anchor Leg Mooring): shallow, calm conditions
  • SPM (Single-Point Mooring): all depths, harsh conditions, limited uptime
  • STL (Submerged Turret Loading): all depths, harsh conditions, high uptime
  • CALM (Catenary Anchor Leg Mooring): shallow, calm conditions

These CNG buoy systems allow loading and offloading in a variety of sea conditions ranging from mild to harsh environments and water depths. Two buoys with associated equipment can be installed at the offshore field loading site to support continuous gas production.