In this work, we present a generic framework for designing on-board decision support systems for marine operations. We discuss different technologies and methods for obtaining and analysing data and providing relevant information to on-board personnel. In particular, we focus on combining and integrating simulators with measurements, both live and stored historical data, in on-board systems for both pre-operational planning and live situation observers that might have predictive functionalities. To exemplify, we present four case studies: The first two are concerned with development of an on-board decision support system for offshore crane operations. Here, vessel motion measurements and numerical models are combined for both on-board surveillance applications and on-board pre-operational planning applications, where the latter include historical vessel characteristics. In the third, we combine simulations, measurements and automatic control in an application aimed at triple-trawl fishing operations. Finally, we present a data-driven decision support system for energy-efficient operation of hybrid propulsion systems.