U.S. Coast Guard Review of Natural Gas Fueled Vessels
Authors: Meyers Timothy , Woessner Nicholas 
Published: April 2012

Abstract
Natural gas used as a shipboard fuel is a leading alternative for meetingcurrent and future air emission requirements, including the limits for EmissionControl Areas adopted in recent amendments to MARPOL Annex VI. Additionally, current pricing and availability makes natural gas highly competitive incomparison to more traditional marine fuels. For these reasons, a number ofcompanies have submitted proposals to the U.S. Coast Guard to incorporatenatural gas fueled systems into their new or existing vessel designs. The useof natural gas onboard ships does pose certain unique technical challenges dueto its intrinsic properties that warrant careful consideration to ensurevessels are designed for safe operation. This paper covers several importanttopics concerning natural gas fueled vessels. They include: the use ofinherently gas safe versus emergency shutdown concepts in system design, natural gas fuel tank location, considerations for hazardous locations, crewtraining requirements and bunkering considerations, as well as the currentreview and approval process for U.S. natural gas-fueled vessel designs.

1. Background
Air pollution prevention requirements are driving the marine industry to seekadvanced technologies to reduce air emissions. Many of the new air emissionreduction systems being considered for use on board vessels have been proven inland based applications, and are now being adapted to the marine environment. One such technology is the use of natural gas as fuel.
Although natural gas fueled ships are not commonplace, the use of natural gasas a transportation fuel has been around for some time. It has beensuccessfully used to power cars and busses in the U.S. for over twenty years. For over 45 years, liquefied natural gas (LNG) cargo ships have used cargoboil-off to fuel their propulsion boilers, and more recently in dual-fuel gasand diesel engines. Since 2000, Norway has authorized LNG fueled ships tooperate within their waters and has acquired significant expertise andexperience in the design, construction, operation, and inspection of thesevessels. Used as a transportation fuel, natural gas is stored as either LNG orcompressed natural gas (CNG). When burned in internal combustion engines, itprovides a significant reduction in air emissions compared to dieselfuel.
The U.S. Coast Guard has reviewed several natural gas fueled vessel conceptdesigns, and has received numerous inquiries from vessel designers, operators, and engine manufacturers considering the use of this technology on commercialvessels. Interest in gas-fueled marine applications has spanned a full range ofvessel types to include passenger vessels, offshore supply vessels, containerRO/RO ships, and towing vessels. It is expected that the U.S. maritime industrywill continue its pursuit of natural gas fueled vessels since air emissionlimits will become stricter over the next several years. Currently, the U.S. Coast Guard is reviewing concept proposals for vessel designs that incorporatethis technology on a case-by-case basis as equivalency requests to existingrequirements under Title 46 of the Code of Federal Regulations (CFR).