One of the first stages during the evaluation of the viability of an Energy Saving Devices (ESDs) for existing ships is a global scan of the field of application, performance and the required investment. Based on this preliminary data the Return on Investment (RoI) for an ESD retrofit can be estimated, which is a key figure in decision making processes. To this end an Early Assessment Tool (EAT) is developed, containing a database of reliable performance data, a patent database, a benefit tool, cost model and an economical tool. The EAT is compatible with container vessels, bulk carriers, tankers, ferries/RoPax vessels and short sea shipping cargo vessels. Integrated ESDs are the pre duct, pre swirl stator, PBCF, rudder fin, rudder bulb-hub cap system, ducts surrounding the propeller, hull fin and the combination of a pre duct and pre swirl stator. The benefit tool calculates the power reduction at a given sailing mode by application of a specific ESD type. The cost tool determines approximate ESD costs, broken down into design, material and installation costs. The economical tool combines output from the benefit and cost tools and calculates the RoI. A web-based EAT for public use and an extensive EAT for project members have been created.