Trelänningen

Trelänningen is a wreck spread out rather than stacked up. The largest coherent piece, about twelve metres by three with hull planking of roughly twenty-centimetre boards over twenty-by-twenty-centimetre frames, sits on a sand bottom at nine to twelve metres on the south side of Trelänningsgrunden shoal, in the outer archipelago east of Hästö-Busö island. The Heritage Agency records further debris on the surrounding slope, a shallower scatter at six to seven metres and outlying timbers around twenty and twenty-four. There is no standing structure or substantial relief. Plan the main fragment first; the deeper outliers are a second-pass option if certification and gas allow. Buoyancy matters even here, since the timbers are fragile and Antiquities Act protected.

A working coastal vessel from somewhere on Finland's west coast came to rest on the Raasepori sand, and almost everything else about it was lost. The Heritage Agency dates the wreck only as historical, undefined; there is no recorded name, no build year, no loss circumstances. The coarse non-oak construction and the Kristiinankaupunki home-port marking are the only structural clues. Two surveys anchor what is known: a 1992 inspection by Museovirasto with Teredo Navalis ry and Piraya ry following Stig-Goran Meyer's report, and a 2021 3D-mapping campaign by Suomen meriarkeologinen seura ry. Beyond the heritage registers and one short YouTube clip, the site has no community footprint.

The boat does the navigation on this one. There is no buoy and no descent line; the skipper sets the GPS mark from the Heritage Agency coordinates and the team plans a free descent and a controlled return to the boat. Drysuit is standard from May through October with cold-water gloves and hood as baseline. Compass and SMB stay standard kit on any open-archipelago dive from a free-floating boat. The position is exposed in any sustained southwesterly or westerly, so plan a sheltered backup such as Hauensuoli on the way back to harbour. The Antiquities Act is categorical: no touching, no lifting, no anchoring on the wreck.