In 1948 Fritjof Gustavsson acquired the boatyard from Bertil Jansson. Fritjof, a brother of five carpenters and boat builders from Håknäs, Vätö, had also worked for a few winters in the 30's at Rosättra. Having a strong inclination for boat building, Fritjof was very keen to take over Rosättra as soon as Bertil invited him to consider that possibility. During the winter of 1948, still with Bertil and co-workers' assistance, Fritjof built 3 large motorboats (13,5 x 3,5 m.) which had been ordered.
In 1948 Bertil spent his last winter at the boatyard as Fritjof took over for him. At this point in time Fritjof had the assistance of 12 employers and an annual turnover of c. 150,000 Crowns. His three sons, who still today have an active role in Rosättra, all started helping their father when they turned fourteen: Ola started in 1950, Jan in 1953 and Mats in 1958.
When Fritjof took over, the boatyard had an area of 600 m2. After one year a forge had been installed and a specialised workshop offered a new range of services, including regular boat maintenance and the wintering of approximately a dozen boats.
In 1949 the boatyard built a sightseeing boat measuring 18x4 m., the largest vessel built so far at Rosättra.
The boat, ordered by Sjöberg, went to Stockholm.
In 1950 Rosättra started building the well-known Laurin Koster boats (Scandinavian double-enders) designed by Arvid Laurin. Laurin Koster boats were made of all mahogany. The first order came from Yngve Cassel, who in 1956 sailed "Casella", a 6-ton boat, over the Atlantic to the West Indies. "Staika III", a sister boat to "Casella", was built in 1957 and become well known for her good performances at the "Fastnet race" and "Gotland runt".
Around 1953 business was less profitable at Rosättra. The boatyard had started building Laurin Koster in the 2.5 ton class, but only had three orders placed for the whole year. In order to avoid laying-off well trained and dedicated personnel, Rosättra accepted a commission to restore woodwork in the churches at Vätö and Björkö-Arholma, where benches, chandeliers and candleholders were made.
Aiming to complement services that were offered, larger sheds were built at the boatyard nearer to the old stocks, with the capacity to hold up to 18-ton vessels. This allowed a dozen boats, usually wintering in the open, to be kept under cover.
Better times arrived to Sweden and Rosättra. In the fall of 1954 a Laurin Koster in the 3.2-ton class (meaning approximately 2,500 hours of labour) started to be built. The boat's owner was Fischer, who used her for many successful regattas.
From 1955, Laurin Koster sailing boats became quite popular. By then, a two-year waiting list was normal, and purchasing a boat could cost up to c. 30,000 Crowns.
At Rosättra 3 pilot-boats were ordered by the Swedish Sailing Association (Svenska Kryssarklubben). In 1957 an even larger (4.5-ton) Laurin Koster boat was built. "Aniara", bought by Göran Curman, was very successful racer. In that same year, commissioned by Tiblom and designed by Reimer, a 10-ton Bermudan ketch sailing boat was built. Another major vessel been built in 1957 was "Cassella II", a 4.5-ton Laurin Koster, which sailed the 1960 Trans Atlantic Race between Skagen and Bermuda.
During the 60's Rosättra sustainable growth required further expansion of infrastructure. In 1959 new facilities for veneering, gluing and delicate woodwork finishing was completed.
Fritjof's sons took much interest in sailing and, unlike their father, all three were keen sailors. Between 1959 and 1963 Ola, Jan and Mats built their own Laurin Koster. Jan, who regularly participated in competitions since 1957, built off-hours his first racing boat, the Laurin Koster "Anonina". He sailed "Gotland Runt", among other major regattas, and become known as one of the best young sailors in the class.
Even Ola, the eldest son, became interested in sailing from early age. He also had his own Laurin Koster ("Soniola" ) and participated in a few of the major coastal and offshore competitions.
Mats, the youngest of the brothers, was no exception and, in his 3.2-ton Laurin Koster "Ancilla", won major trophies at the "Gotland runt" and "Åland Sea Race" competitions..
In 1963, Rosättra become a Limited Liability Company with Ola, Jan and Mats Gustavsson as associates.
In 1966-67 Curman ordered the 6-ton Laurin Koster "Aniara II". Mats, shortly afterwards, built a sister boat to Aniara II, but this time according to the IOR rule system, which performed extraordinarily well at the Skaw Race and One-ton trophy (Kiel).
By the late 60's the golden times of wooden boats were over and not many new ones were being built. One of the last Laurin Koster was built at Rosättra in 1967-68.
The production of family cruisers went from wood to GRP, and Rosättra evolved into combining both worlds, developing GRP hulls and keeping the superior wood interiors. In 1971 the Boatyard acquired 10,000 M2 of land from Hjalmar Jansson of Rosättra Estate. The plot was situated 200 meters from the water, which required the use of tractors and boat trailers for the launching and laying up of boats. The new ground allowed for the construction of large winter storage facilities and c. 170 boats could be wintered under 2,400 M2 of roof.
From the early 70's the production of plastic boats become quite competitive. Rosättra Boatyard began planning the construction of a fast family cruiser that could combine the beauty of traditional wood craftsmanship in a GRP hull: the new Linjett 30 - and with it a whole new era - was to be born.