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Videoray - News - April 13, 2005


An underwater project, begun by a diver in Scilly and ongoing for the past 36 years, is about to benefit from the use of modern, underwater technology, in the form of a state of the art Remote Operated Vehicle.

This ROV could go on to revolutionise seabed exploration in islands strewn with shipwrecks. The project began in 1969, two years after Royal Navy divers found the 1707 wreck of Admiral Sir Clowdisley Shovell's HMS Association.

Scilly-based Richard Larn, an acknowledged authority on shipwrecks and author of the definitive Lloyd's Shipwreck Index noticed, during survey work, that some of the cannons on the deep Tearing Ledge wreck site now confirmed as the Eagle - another casualty of the 1707 disaster - seemed to have what can only be described as protruding 'fins'.

Over the following two years, as the same Navy team extended their search area looking for yet another of the fleet's casualties, the Romney, Richard found that nine out of 19 cannon on another deep wreck on the western edge of the Crim Rocks had the same unusual feature, and discussed it with team member Roy Graham, also now resident on Scilly.

Between them a survey was made of the site, the cannons tagged, and detailed measurements taken of a number of cannon carrying these 'fins', which were turned into proper drawings by Richard. Later, two other cannon sites on the Crim, located between Zantmans Rock and North Rock, both deeper than 100ft, were found to have 'finned' guns, several of which were photographed and measured in detail.

Whether or not these three Crim sites are interrelated has yet to be established but the coincidence of 'finned' cannon suggests they are and it may be possible to link these sites with one or more of the many armed shipwrecks known to have been lost amongst the Western rocks whose location still remains unknown.

The conundrum centred on the purpose of these 'fins'; if indeed they had a purpose, and if not, what caused them?

On average they are some 20 inches in length, and lie parallel with the bore of the cannon, centre-line or offset, often in pairs, standing three-four inches tall. Were they some sort of sighting attachment, possibly 'cooling fins', some aspect of ship gunnery long forgotten, or simply some strange electrolytic action?

Cannon experts such as Colin Carpenter, the Tower of London, Woolwich Arsenal and the Totnes English Heritage cannon workshops were consulted, but none had seen them before.

Richard has since made a study of 'finned' cannon, recording many examples on the Association (1707), Coronation(1691), Dartmouth (1690), Salcombe harbour wreck (c1700) and elsewhere, the sites seemingly confined mostly to the sea around Devon and Cornwall.

The irregularity, random positioning and angularity on iron cannon of these 'fins', plus a complete absence of any documentation or recording in the history of gun-founding, is reasonable confirmation they were not deliberate attachments, but a long-term natural function of electrolytic corrosion of iron in saltwater, but why on some cannon and not others?

More evidence is required, and this is where David McBride's new underwater ROV will feature. Assisted by islanders Sean Lewis, Terry Parsons and Mike Brown together with Peter Holt of Sonardyne Ltd, Richard Larn and technical diver Chris Lobb, of Kernow Divers, the team, weather permitting, intend to continue previous work on these deep Crim sites in 2005-6 where cannon were laboriously re-numbered and tagged by hand in 1996.

Since then trials by the team of a 'homemade' ROV proved unsatisfactory due to flooding or electronic breakdown, and the purchase of professional equipment became the obvious choice.

The advantage of an ROV is that its high-resolution video camera, with surface monitoring screen and integrated DGPS positioning, will allow huge areas of deep water to be searched methodically down to 500ft, well beyond safe diving depth.

This ROV can achieve in one eight-hour working day, tidal conditions permitting, the equivalent of 30 days deep diving, without anyone risking the 'bends', which with the nearest compression chamber 90 miles away from Scilly in Plymouth, by search and rescue helicopter, has to be avoided at all costs.

With the advantage of continuous photography, video or stills, colour or black and white, built in underwater lighting, and a manipulator arm that can place a scaled rod on a cannon or artefact for measuring purposes, this opens up vast areas of deep seabed around Scilly to exploration, photography and recording for the first time.

The unit also has huge commercial potential, capable of producing high resolution underwater video recording of piers, piling, concrete structures, moorings, archaeological sites, ship damage and scallop dredging and fishing trawl ecological damage, cheaper, faster and safer than any commercial diving operation.

In anticipation that 'finned' cannon exist elsewhere, articles are being placed in several diving magazines and journals inviting response. Professional support has been sought from David Gregory, senior chemist at the Danish Roskilda Viking Museum, who will be sent 'fin' samples for analysis; Alex Hildred, armament expert for the Mary Rose Trust; and English Heritage.

It is hoped that the loan of underwater data logging equipment can be achieved through Wessex Archaeology, which can be placed on these deep-water sites, to establish salinity, temperature, ph, dissolved oxygen and tidal current flow over 'finned' cannon sites on Scilly, since this may reveal conditions of unusual electrolytic action.


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