Ideologies, instruments and institutions that promote ocean energies (OE), a marine renewable including wave and tidal devices technologies, are exam- ined within an ecological modernisation (EM) perspective. EM type argu- ments provide ideological justification for OE projects, but are vulnerable to environmental and cost critiques. Already, large tidal barrage projects have faced opposition from environmentalists, even though they offer significant generation capacity. Unlike wind energy, where grassroots activists played a vital role, the strongest institutional advocates for OE are larger firms, universities, and specialist agencies, together with sub-national governments. Regarding instruments, the overall amount of subsidies combined with political support seems more important than feed-in tariffs. Given a backlash against renewables and a competing offshore wind sector, it remains unclear whether a blue growth ecological modernisation strategy can promote what remains a Cinderella renewable.