Natural gas is becoming the “fuel of choice” for the maritime industry, not only for its potential in reducing environmentally hazardous gas emissions, but also for its reduced cost when compared to other fossil fuel-based alternatives.

For natural gas to become a preferred marine fuel, its availability needs to improve, and this fact alone has hindered its growth in some parts of the world, according to Robert Allan Ltd., Vancouver, British Columbia. Some of RAL's clients are actively engaged in developing the required infrastructure to make natural gas more readily available.

RAL and MTU Friedrichshafen GmbH say they recognized these new market opportunities, took action, and developed the first natural gas-fueled shallow draft pushboat design — the RApide 2800-G pushboat.

The project is a preliminary design which utilized the shallow draft RApide 2800-Z2 pushboat that currently operates on the Amazon River system. The vessel design was modified to suit a complete LNG (liquified natural gas) propulsion system with two 746-kW MTU 8V4000M55R-N Tier III gas safe main engines. Additional to the engines, MTU also acts as the system integrator, which means that MTU will also provide the complete LNG package — LNG tank system and an integrated ship monitoring, LNG control and safety systems, RAL said.

While keeping the existing hull shape, the design was reconfigured to allow the installation of the LNG tank while still providing adequate space for other machinery and a comfortable work environment for the crew. The lower crew cabins, mess, and galley moved up a deck and the deckhouse was enlarged. The project complies with the rules for the gas system hazardous zones of a compact 28-meter (92') tug. To ensure redundancy there are two independent tank connection spaces attached to the LNG tank, one for each engine.

For continuous operation on a river system, the design accommodates a crew of 14, with master and chief engineer having single cabins and double cabins for the balance of the crew.

The vessel is designed to comply with DNV-GL rules (with the following notations: INLAND NAVIGATION VESSELS (RU-INV) ✠ 1A Z PUSHER, GAS FUELLED) and is currently undergoing an “approval in principle” review.

Specs include:

  • Length overall: 28.0 m (92')
  • Beam, moulded: 10.5 m (34.4')
  • Depth, moulded: 3.2 m (10.5')
  • Draft, maximum: 2.5 m (8.2')

Approximate tank capacities:

  • LNG (gross): 70.0 m3
  • Fuel oil: 19.2 m3
  • Potable water: 26.6 m3
  • Water ballast: 47.9 m3
  • Sewage: 5.6 m3