Åke Johansson (born 1917) started building S/Y Kersti in 1957, launching her at the slipway in Eskilstuna (on Lake Mälaren some 60 miles west of Stockholm) three years later. Åke was no beginner at marine constructions, previously having built a number of sailing and paddle canoes and a Mälar 25 yacht.

S/Y Kersti's designer, Gustav Plym, was an internationally renowned sailing personality with an advanced position in Fastnet Race 1957 among his racing merits. Plym designed S/Y Kersti's sister S/Y Elseli IV a few years before. It was these drawings that Åke bought from Plym and partly modified by adding approximately one foot to the stern, lending his boat a more harmonious profile. So S/Y Kersti is one of a kind, having only one sister.

Åke was well helped by his eldest son Krister during the building of S/Y Kersti. The only thing not built from scratch was the main mast which was bought from Schelin's Boat Yard at Kungsör. Åke ordered the mast in a square shape but when it arrived it showed to be octagonal. The yard thought that there would be enough planing for Åke to do anyway on the 50-foot mast, knowing he wasn't too keen on electric tools. Except for a band-saw, a drilling machine and a finishing sander, no other electric tools were used in building S/Y Kersti. The mould for the ballast keel was borrowed from Schelin's who had kept it after the building of S/Y Elseli IV.

The first summer with S/Y Kersti the Johansson family including four children sailed to Kalmar on the Swedish east coast and on to the island of Öland.

Mälarbaden outside Eskilstuna has been S/Y Kersti's home port from where Åke has taken her on voyages throughout Lake Mälaren and into the Baltic. Åke has participated in 24-hour races for many years and also carried out some longer trips in the autumn.