- News - April 13, 2005
VEHICLE TO HELP SOLVE CANNON MYSTERY
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
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
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
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
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.