Märket lighthouse, situated right on the border of Finland and Sweden, opened in 1885. The light apparatus was a Frenchmade Fresnel. The rotating lens drum and the arrangement of lenses and prisms made Märket Finland’s first lighthouse with a flashing light characteristic. The characteristic for Märket was ten white flashes per minute that alternated from weaker to stronger. The reach of the signal was 8.5 nautical miles. The apparatus was fuelled with kerosene until 1956 when it was electrified. Märket’s apparatus consisted of clockwork and a fuel tank.
The clockwork rotated the lens while the wings controlled the speed at which it rotated. The lead weights hung from the clockwork were wound up manually. The clockwork itself was located under the lens in the lantern room. The lens rotated three hours at a time before it had to be wound up by the lighthouse keeper. Märket lighthouse was manned until 1976 and was the last of the Finnish lighthouses to be automated.

The Plimsoll line is important from a safety perspective. It indicates how deeply a ship can be loaded in various water types and temperatures to keep its buoyancy and stability. The starting point is the maximum draft in sea water, which is marked by the horizontal line of the Plimsoll line and by loading mark S (summer temperate seawater). The remaining lines mark maximum draft in tropical fresh water (TF), tropical seawater (T), winter temperate seawater (W) and winter in the North Atlantic (WNA). The two letters either side of the main line indicate the classification company of the ship. The Plimsoll line was named after the British politician Samuel Plimsoll (1824-1898). He was heavily engaged in issues concerning safety at sea and fought hard against shipowners who deliberately risked the lives of sailors by overloading their ships. It was on his initiative the now obligatory loading line on ships was introduced, an achievement that bestowed him with the epithet sailor’s friend.

It was late at night on 14 December 1933 when the crew of iron barque PLUS signalled for a pilot outside Kobba klintar pilot station. As none was available, the captain was left with no choice but to try to sail in to Mariehamn unaided. But in the howling winds and thick snowfall PLUS lost her course and ran aground, tearing a big hole in her hull. The hold filled with water so quickly that there was no time to lower the lifeboats; the entire crew plunged into the icy water to try and swim ashore. Only four of them managed to reach Korsö where they were helped by the island’s lighthouse keeper; the other 12 men lost their lives.