HM Frigate Unicorn

Immediately on launching, Unicorn was placed in reserve (put "into ordinary"). To protect her hull from rainwater, the dockyard constructed a roof over the full length of the main deck. This roof stilll largely exists and reflects the changing maritime technology and the requirements of the navy: Unicorn has never been masted or put to sea other than to be towed from Chatham to Dundee in 1860, where she served as a drill ship until 1968 for the local naval reserves. The consequence of this history is that Unicorn has never been modified or restored in any significant way - she is the oldest most original ship still afloat in the world. 

The new roof is an extension of the original 19th century roof and restores full protection to the hull of the ship from the most damaging effects of rainwater. Working together with Mackays, ( we devised a lightweight carpentered-timber structure that takes its form from the existing original roof. The design of the new roof was complicated by the necessity to provide a robust structure that would withstand the high wind loads to which it would be subjected whilst having minimal impact on the existing fabric of the ship - an artefact of unique importance.  In addition, with Unicorn being a floating structure, we had to be careful that the extension of the roof right over the prow of the ship did not have an adverse effect on her trim - some restowing of cast iron ballast was undertaken as part of the work to balance the weight of the new roof, whose weight was kept to a sensible minimum.  And of course, all this had to be done whilst working over water.

So all in all, something of an unusual project for us as structural engineers, used to working on dry land on things that stay still!



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