During the next years the marine industry has to expect additional challenges by fluctuating fuel prices, an increased fuel diversity, extended emission regulations as well as a higher sensitivity of the public and the politics with regard to environmental protection. New built vessels will be equipped with further technologies to cope with the before mentioned challenges. But is there a possibility to make existing vessels, fit for the future – at least partly? Could be a dual-fuel (DF) retrofit with the possibility to operate on natural gas, respectively LNG, seen as a solution for this? The paper will show and discuss potential technology approaches. In all cases a further modification of the engine (e. g. compression ratio, piston bowl shape, TC specification adaption, safety technology, …) must be executed in addition. Although this improves the operation in gas mode, both the technical and economic feasibility have to be evaluated for each project. As example for such DF-retrofit project the executed conversion of a high-performance Diesel engine for Fred. Olsen Express SA, operating high-speed craft vessels on the Canary Islands, will be presented. The potentials and challenges of this conversion have been evaluated in detail before execution. The gained operational results fulfilled the expectations of the customer fully and got complete approval by the involved classification society.