Ice has long been a serious problem for shipping. For centuries, northern ports, particularly in the Baltic and Northern Russia, would spend several months of the year icebound and unable to take part in the benefits of maritime trade. In special circumstances, a port might cut a channel through the ice, as Boston did to free the Cunard liner Britannia in 1844, but this was rare due to its difficulty. It wasn't until the dawn of the 20th century that a way was found to reliably break ice and let merchant ships through.1

Britannia leaving Boston
The first modern icebreaker was designed and built in Britain for the Russians, and named Yermak. She entered service in 1899, and served in the Baltic until 1963, a testament to the soundness of her design. Yermak had all of the features common to modern icebreakers: a heavily reinforced, rounded hull; a steep slope to the bottom of the bow to let it ride up on the ice, and lots of power. Icebreakers don't do their job by simply cleaving ice in two. Instead, they take advantage of ice's low flexural strength to ride up on top of the ice and break it with their weight. With extremely thick ice, such as pressure ridges, this can mean essentially beaching the icebreaker on top of the ice, or even having to back off and hit the ice at full power several times. In most cases, though, nothing this violent is needed and the ship simply pushes the ice down under her hull, fracturing it as she goes. Read more...
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