A dual-fuel conversion for the 3406-B Caterpillar marine diesel engine has been developed. The purpose of this conversion is to use lower priced natural gas as a fuel, thus providing substantial cost savings for large fuel consumers.The conversion applies dual-fuel technology to the smaller high-speed direct-injected diesel engine. Parameters are identified which allow a dual-fuel conversion to operate with similar performance as a diesel engine while simultaneously maintaining parameters that promote engine life. Test data is presented comparing various characteristics of both dual-fuel and diesel operation.Details of the conversion system are given. Data is presented showing fuel consumption, conditions leading to engine knock, conditions promoting methane flame propagation, and air-fuel ratios required for efficient combustion. The system resulting from this study will use Liquefied Natural Gas (LNG) to power a dual-fuel conversion of a shrimp boat's main engine and generator set. The cold temperatures of the LNG will also be used as a heat sink to refrigerate the fish-hold area of the boat.