A landmark in maritime history

HM Frigate Unicorn is more than a Dundee visitor attraction, says Emeritus Professor David Bradley of Abertay University

Many would imagine that the most noteworthy thing about Frigate Unicorn is her longevity. Closer inspection, however, reveals that she is an example of a key moment in the design of naval vessels, one that resulted in the transformation over the 100 years from 1805 to 1906 of navies based on sail warships – the Wooden Walls – to ones based on armoured and steam-powered vessels – the Dreadnoughts.

To understand how huge this change was, imagine you were a seaman on Henry VIII’s Mary Rose in 1545. Then go forward 260 years to HMS Victory at the Battle of Trafalgar in 1805. Although there would be some differences, Victory essentially sailed and functioned in exactly the same manner as the Mary Rose. However, go forward another hundred years, to 1906 and HMS Dreadnought and you would be in an entirely alien environment. Gone are the sails and the wooden construction, replaced by steam turbines and steel armour. Gone are the rows of muzzle loading cannon with ranges of two to 3,000 metres to be replaced by turrets carrying breech loading guns capable of firing 12in explosive shells weighing 850lbs distances in excess of 12 miles.

In this context, Frigate Unicorn represents a significant transitional stage in warship design in which the use of new materials, such as wrought iron, enabled design changes which significantly improved areas including hull performance, sailing qualities and seakeeping.

In the early part of the 19th Century, the design of a ship’s hull changed slowly, based on a process of making small incremental alterations and then evaluating each one. If a change proved beneficial, it was carried forward to other ships; if not it was rejected.

By 1822 when Unicorn was laid down, the basic hull form remained viable, but developments in manufacturing technology were also making new materials, such as wrought iron of consistent quality, more readily available. At the same time, an increasing shortage of wood meant naval architects were increasingly looking to utilise such materials.

Among those leading these innovative developments was Robert Seppings who became joint Surveyor of the Navy in 1813. As Surveyor, Seppings assumed overall responsibility for the design and construction of Royal Navy vessels at the Royal Dockyards and oversaw the introduction of a number of major design developments in ships built under his charge, all of which can been seen in Unicorn, which was herself laid down at Chatham in 1822 and launched in 1824.

Seppings introduced a rounded stern, adding strength to what had conventionally been a weak point of the hull, as well as wrought iron knees to support the deck beams and transfer load to the frames and diagonal and other bracing in the form of wrought iron straps throughout the lower hull.

These changes improved seakeeping – the way a boat goes through the waves – while also making her a drier ship and reducing maintenance. All of these developments improved a vessel’s ability to remain at sea for long periods.

They also increased the resistance of the hull to gunfire, at least with regard to the roundshot used by contemporary cannon, while providing a more robust gun platform in return.

However, despite the design innovations involved in her construction, Frigate Unicorn also represents the end of the sailing ship navy. In 1827, three years after Unicorn was launched, came the Battle of Navarino Bay, the last fought entirely by sailing warships. The next day, the steam warship Karteria, designed and built at Rotherhide on the Thames and in service with the Greek navy, entered the bay.