[4] During his academic years Jakopin spent his weekends in the Croatian seaside town of Punat building do-it-yourself boats, and later learned the charter yacht business.

By 2000 Seaway became the only independent company outside major yacht builders that could engage in the entire development process - from design to prototype and final moulds, and its revenue grew to 6.6 million euros.

Investment enabled the purchase of a robot for precise prototype and mould production, required by Seaway's customers and acquisition of new, larger premises for installation of the new tool.

[13][14] Hybrid technology was also applied to a Seaway's sailing boat, to the Shipman 59 Carbon, designed together with Doug Peterson and the French naval architect Guillaume Verdier.

[15][16] In 2014 Seaway was in no shortage of orders for boats, but the enduring credit crunch after the 2008 crisis crippled further production and in 2015 both divisions of the company went out of business.

[17] In the meantime Jakopin brothers reestablished J&J Design as an independent company[18][19] while the boatbuilding part of Seaway (Greenline and Shipman families) was taken over by SVP Yachts (Vladimir Zinchenko).

[26] During the Boat Builder Awards 2024 event in Amsterdam, organized by RAI Amsterdam and Boat International Media, Japec and Jernej Jakopin, the founders of J&J Design, were awarded the title of "Designer of the Year", as pioneers in carbon epoxy and hybrid power technologies as well as for their influence across a wide part of the boatbuilding industry.

[25] Jakopin was engaged in promoting new ideas in naval design, especially in the area of hybrid boat propulsion and environment friendly technologies, through lectures,[27][28] public presentations[29][30] and work in professional associations such as the Slovenian Academy of Engineering.

[32] At the Freediving Indoor World Championship 2022, in June in Belgrade, Serbia he repeated the achievement from Kaş in Masters 70+ category, in Bifins (164 m), Monofin (186 m) and Static apnea (7 minutes 6 seconds) disciplines.