HMS Alarm (1758)
| History | |
|---|---|
 Great Britain
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| Name: | HMS Alarm |
| Builder: | Barnard, Harwich |
| Launched: | 19 September 1758 |
| Fate: | Broken up September 1812 |
| General characteristics | |
| Class and type: | Niger-class fifth-rate frigate |
| Tons burthen: | 683 bm |
| Length: | 125 ft (38 m) |
| Beam: | 35 ft 6 in (10.82 m) |
| Sail plan: | Full-rigged ship |
| Armament: | |
HMS Alarm was a 32-gun fifth rate Niger-class frigate of the Royal Navy, and was the first Royal Navy ship to bear this name. Copper-sheathed in 1761, she was the first ship in the Royal Navy to have a fully copper-sheathed hull.
Alarm initially saw deployment in the West Indies, where she experimentally had her hull sheathed in a thin layer of copper. Firstly it was intended to reduce the considerable damage caused by the teredo woodworm , and secondly the well-established toxic property of copper was expected to lessen the speed-killing barnacle growth which always occurred on ships' hulls.Alarm’s hull was first covered with soft stuff, which was hair, yarn and brown paper, and then covered with a layer of copper plates.
After a two-year deployment to the West Indies, Alarm was beached in order to examine the effects of the experiment. The copper had performed very well in protecting the hull from invasion by worm, and in preventing the growth of weed, for when in contact with water, the copper produced a poisonous film, composed mainly of oxychloride, that deterred these marine creatures. Furthermore, as this film was slightly soluble it gradually washed away, leaving no way in which marine life could attach itself to the ship. Satisfied that the copper had had the desired effect, the Admiralty introduced copper sheathing on a number of frigates.
In 1776 Alarm was resurveyed. It was soon discovered that the sheathing had become detached from the hull in many places because the iron nails which had been used to fasten the copper to the timbers had been ‘much rotted’. Closer inspection revealed that some nails, which were less corroded, were insulated from the copper by brown paper which was trapped under the nail head. The copper had been delivered to the dockyard wrapped in the paper which was not removed before the sheets were nailed to the hull. The obvious conclusion therefore, and the one which had been highlighted in a separate report to the Admiralty in as early as 1763, was that iron should not be allowed direct contact with copper in a sea water environment if severe corrosion of the iron was to be avoided. Later ships were designed with this in mind. The Admiralty had largely suspended the programme of fitting ships with copper sheathing after the 1763 report, and had not shown any further interest in developing effective copper sheathing until 1775. In the meantime the copper sheathing was removed from Alarm, and several other test vessels until an effective solution to the corrosion problem could be developed.
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