The idea came out of a sailing trip aboard Imme Gram, combined with news of the Skuldelev wrecks then being recovered from Roskilde Fjord. Five ships had been sunk there deliberately, blocking the approach to Roskilde against invasion, and they were salvaged between 1957 and 1962. Wreck number five was a snekkja — a small longship built near Roskilde around 1030, about 17 metres long, pulled by 26 oars. A group of local volunteers on Als, a great many of them Augustenborg scouts, decided to build one. They worked from the first crude drawings off the archaeological dig, because the archaeologists wanted an accurate replica badly enough to hand over provisional plans: a working ship would teach them things the timbers could not. The local blacksmith forged copies of Viking-age tools, mainly adzes, from period finds. No shipyard on the island had room, so the hull went up in the Augustenborg lumber yard, and she was launched in 1969.

Skuldelev 5 was preserved well enough that wear marks from the original rigging survived in the wood — but wear marks tell you where lines ran, not how a ship handles. Sebbe's mast and rig were reconstructed from those marks and then argued with, at sea, for years. She ended up with a 45-square-metre square sail carrying only the top yard, and a steering oar angled at about 25 degrees instead of the vertical position first planned. The results reset expectations. She is poor at tacking: 45 degrees to the wind on a good day, and in a headwind it is genuinely faster to take down the sail and row. Off the wind she is roughly twice as fast as the original calculations suggested, running 12 knots on a half wind, and a motivated crew can row her at six. What the trials mostly produced was respect for the shipwrights of the eleventh century.

The 1972 Hedeby–Kaupang run remains the ship's longest passage under her own power, and it did what experimental archaeology is supposed to do: it moved a saga's claim from the category of boast into the category of plausible. Four years later Sebbe went considerably further. She took part in the United States bicentennial in 1976, sailing mostly on the Hudson River at New York as a guest of the Hudson River Sloop Clearwater, the folk singer Pete Seeger and the Clearwater organisation. She did not cross the Atlantic on her own bottom — she travelled as deck cargo on a modern ship, and the crew flew. Every year since, she has made a summer cruise of one to three weeks, and by now she has worked most of the Danish and north German coasts.

The type is unusual enough that the Danish Maritime Authority wrote a bespoke rulebook for her, revised every few years. Despite her tiny tonnage, the master must hold at least a Yacht Master Third Class licence, and she cannot sail with fewer than eleven crew. That floor is not bureaucratic caution; it is roughly the number of hands the ship needs. She is owned by Vikingeskibslaget Sebbe Als, the Sebbe Als Viking Ship Guild, a self-owning association with members across Denmark, in neighbouring countries and in the United States. The guild also keeps Ottar Als — a Faroese boat, strictly speaking, used for training and pleasure — and Fie Als, a small glass-fibre boat with an outboard that serves as safety craft and tug on longer trips or with green crews.

When the Augustenborg lumber yard closed and a yacht harbour took its place, the guild built a naust — the traditional Norwegian boathouse — about half a nautical mile away. Sebbe is hauled into it every winter, and most of her maintenance happens there on work weekends: a rotating volunteer crew, cold hands, tar and timber. Fifty-odd years of that has produced Denmark's oldest sailing 'fiver', and a great deal of transferable knowledge. Much of what was learned handling Sebbe fed into later reconstructions, including Havhingsten fra Glendalough, the Sea Stallion from Glendalough. She also turns up regularly in films and television about the Viking age, which is a strange afterlife for a scout project — though anyone who has spent a February weekend in the naust would tell you the filming is the easy part.