For 46 years from 1870 to 1916, Frederikshavn developed into a large industrial town. The town's population grew at a rate of 400 % and every month a new housing development was built. A large harbour was built for Denmark's largest fishing fleet and new ferry routes were introduced to many destinations around the world. The town's shipyards and engine factories supplied the local, national and international markets with ships, engines, gears and propellers.
When the gunboat war ended in 1813, Denmark was bankrupt. The Vienna Congress gave Norway to Sweden without permission from the Norwegians and all the overseas connections were lost and had to be built up again. The main winner of the Napoleon War was England but the victory was a Pyrrhic (hollow) victory as England was on the verge of economic collapse and all imports into the country were either prohibited or had heavy customs duties added to them. So the large market which Denmark had relied upon before the war had more or less disappeared.
Fladstrand now changed its name to Frederikshavn after decree from King Frederik 6th and the town managed to hold on to what it had won. To protect the harbour from being given away, a Royal Harbour Commission was set up in 1822, which meant that the state now owned the harbour. This was the case up until 2000 when the local authority took over the harbour.
The harbour became important for the export of oysters and the royal privileged oyster fishing industry north of Holmene to Aalbaek was a lucrative business. The trade with Norway did not stop completely and lots of ships stopped at Frederikshavn on their route between the Baltic Sea and the North Sea.
The harbour was still too small according to the local traders and it was not until around 1834 that the export to England started once again after the abolishment of duty rates.
The businesses in Frederikshavn gradually became bigger with the import of iron and wood and the export of agricultural products. The harbour was extended a few times and acquired a wharf for the new steam ships made of iron. The first actual sea route from Frederikshavn to Christiansand in Norway was started in 1850 and this was soon extended with more sea routes to Oslo, Gothenburg, Kiel and the important route to Copenhagen. Besides these there were also the permanent routes to England and the USA.
The two largest local traders were two men called, Kall and Cloos. In addition to their businesses, Kall had his own salvage steamship and Cloos was a ship owner. Cloos became one of the largest importers of feeding stuff and fertilizers to Denmark.
There has been heavy shipping traffic around Skagen's Gren since the Middle Ages. Wrecks found stranded along the coast tell their own story. There were so many court cases about stranded goods and what to do with the wrecks that they affected the law and regulations.
The demand increased for another emergency harbour to be built in the Kattegat because the shipping traffic was increasing with more ships and heavier tonnage.
In 1848, the shipping insurance company, Lloyds of London, tried to build an emergency harbour at Graesholmene. The plans were discarded until the end of the 1870's, when local, national and international demands increased to such an extent that the government decided to look into the possibility of building an emergency harbour for the merchant shipping in the Kattegat.