Dekke was born in Bergen, Norway. He was the son of Johan Mungaard Dekke (1802–74) and Christine Marie Hansen (1809–1880). His father was a master baker and he grew up in his father's bakery courtyard on
Strandgaten in Bergen. In 1844, he entered the
Bergen Cathedral School. In 1848, he started an apprenticeship at
Georgernes Verft on the peninsula of
Nordnes. In 1852, after four years of apprenticeship, he traveled to the United States to continue his education, mainly at the East Boston shipyard of
Donald McKay. Upon his return to Bergen, he bought one half in Georgernes Verft (the other half was owned by Herman Brunchorst) and from 1854 the shipyard operated under the name Brunchorst & Dekke. That same year, Jens Gran, who had also worked with McKay, joined the shipyard at Bergen. Dekke and Gran revolutionized shipbuilding in the Bergen area. Under his leadership, the shipyard built 41 schooners and 14 steamships. From 1857 he was the sole owner of the yard, except during the periods 1871-1874 and 1874–1882, when respectively Adolf Tidemand and Georg Smitt were co-owners. ==Personal life==