A pilot-fuel-utilizing vessel engine system which is equipped with a fuel gas injection valve disposed in a diesel engine in order to inject a fuel gas and a fuel oil injection valve disposed on the diesel engine in order to inject a fuel oil, and which injects a pilot fuel from the fuel oil injection valve when the engine is to be operated to serve as an ignition source that ignites the fuel gas injected from the fuel gas injection valve, said system being configured such that a water emulsion fuel or a multilayered fuel comprising multiple fuel oil layers and water layers is used as the pilot fuel.
