When science leaves the laboratory and heads out onto the pontoons, the change of perspective is complete. This is what the OSO summer school offers, co-organised by the Astrolabe Expéditions association, the IMT Atlantique fablab, and the IUEM-UBO. The idea? To devote a few days to an intensive, collaborative programme, to advance concrete projects in open-source oceanographic instrumentation. We bring together a wide range of participants around field projects, in hackathon style, with rapid prototyping, sea trials, mini-conferences and a focus on the full lifecycle of the devices: from the scientific need right through to their use in citizen science. Thanks to funding from ISblue under the PIM scheme, the summer school is accessible: refresher workshops allow anyone to take part, without any prior technical knowledge. “We learnt how to solder, how to model, and how a sensor works. I used to be scared of electronics. Now I realise it’s doable, that you can even turn it into something useful,” says one participant.