CISMAS

Mount's Bay Maritime Survey

 

Background

Mount’s Bay - in the far south west of Cornwall - takes its name from the bay’s most prominent feature, St Michael’s Mount. The economy and transport links of the region have always been closely linked to the sea. Until the nineteenth century the sea was the only practical means of transporting goods to and from the region. Fishing has always been an important activity, and although the fishing industry is now in decline, Newlyn in Mount’s Bay is now home to the largest fishing fleet in the UK.


Surveying south of St Michael’s Mount

St Michael’s Mount is mentioned in classical sources (Pytheas writing in 325BC) as the place (Ictis) where tin was traded from. There has been a harbour on the Mount since at least 400BC.

The Project

Aims

  • Identify surviving historic wreck material within Mount’s Bay
  • Record and survey the wrecks identified.
  • Increase public awareness and appreciation of the local maritime heritage
  • Involve local people in the process of discovering the region’s maritime heritage
  • Provide training in maritime archaeology to enable the above aims.


St Michael’s Mount and Mount’s Bay from Penzance

Scope

The Mount’s Bay Survey took over two years to complete. A further six months was required to produce the project report. There were three main stages to the survey. Firstly, the area was surveyed using remote sensing devices (sidescan sonar and marine magnetometer). This identified potential targets on the seabed. Secondly, divers inspected these targets to establish what they were. Finally, targets of historic importance were recorded.

The survey began in August 2006 and employed a digital sidescan sonar purchased with the aid of a grant from the Heritage Lottery Fund. The survey also used a caesium vapour magnetometer, which was loaned to CISMAS by St Andrews University.

The CISMAS CMax digital sidescan sonar
The CISMAS CMax digital sidescan sonar

Geometrics G-881 marine magnetometer

 

Due to the large area of Mount’s Bay the principal geophysical survey was focused on the body of water between Penzance and St. Michael’s Mount, extending south as far as the 20m depth contour. The geophysical survey, conducted over three seasons of field-work (2006 – 2008), covered a total area of approximately 10 km2.


Mount’s Bay sidescan sonar coverage to date.

Results

The geophysical survey produced a total of 831 targets, of which 733 were Sidescan sonar targets and 98 were magnetometer targets. It was clear that it would not be possible to investigate all of these. In total 85 targets were investigated by the dive team. The results of these dives are summarized below.

Search Result

2006

2007

2008

Total

Anchors

0

7

1

8

Debris

2

2

4

8

Wreck

3

1

2

6

Fishing gear

2

15

1

18

Rocks

1

20

9

30

Nothing found

1

11

2

14

         

Total

 

 

 

85

Summary of diver searches

 

Distribution of objects found, grouped by object type

Undoubtedly the most significant discovery of the survey was the small nineteenth-century composite sailing vessel B022. This site is located less than 200m from the known wreck of the Alice Marie, one of the most popular dive sites in the bay.

Target No

B022

Position

321966E 5553184N

Chart depth

19m

Vessel name

Unknown

Vessel type

Composite sail

Built

1860-80

Length

>16m

Tonnage

Unknown

Wrecked

1884-88?

 
Sidescan sonar image of target B022

It is remarkable that this small wreck had not been discovered by any of the hundreds of divers visiting the site of the Alice Marie. It was clear that this site had not been previously dived from the wealth of material lying undisturbed on the seabed including the ship’s bell, a maker’s plate and numerous other small objects.

 

Outline survey of small composite sailing vessel B022

 

Target No

A837

Position

319248E 5552113N

Chart depth

20m

Vessel name

Unknown

Vessel type

Iron

Built

19th century

Length

?

Tonnage

?

Wrecked

?

  Sidescan sonar image of target A837, part of an iron vessel

This piece of wreck produced a very distinctive Sidescan sonar target. On investigation this was found to be a small section of an iron ship in 20m of water. The wreckage consists of a section of hull plating 6.2m x 2.1m lying flat on the seabed. There is no other iron debris in the vicinity, so it is hard to account for this isolated piece of wreck. The most likely explanation is that this was deliberately dumped, probably from a 19th century vessel.

 

Outline survey of target A837 - a section of an iron vessel

 

As well as searching for new wrecks, CISMAS also undertook Sidescan sonar surveys of certain known wrecks within Mount’s Bay. Below is a Sidescan sonar image of the popular dive-site SS Hellopes, which sank in the bay in the late 19th century.

Sidescan sonar image of the iron steamship Hellopes

 

Mount’s Bay is used today as an anchorage for ships sheltering from severe weather; this would also have been true in historic times. In total eight anchors were located by the survey, ranging in date from the early 19th century to the present day.

Diver and 20th century Stockless anchor
Sidescan sonar image of anchor B633

 

Numerous items which are not a wreck or anchor but are still man-made were located during the survey. In some cases the remains may be an indication of wreck in the vicinity but are alone not substantial enough to constitute wreckage. Other material found range from abandoned fishing gear to target B359, a possible parachute mine.

Above: Sidescan sonar image of target B359

Left: Underwater photograph showing the fins on the end of target B359. The scale has 0.10m divisions.

 

One less tangible result of this survey was the skills the group developed in this type of work. CISMAS members have now accumulated a great deal of knowledge of marine geophysical survey and underwater searching; this in a group comprising people of many different backgrounds, ages and vocations. The project was open to all members of the community.

St. Michael’s Mount

CISMAS hope to continue searching the Mount’s Bay area. We intend to start working from the area already covered towards the shore. This shallow water is more likely to contain wreck remains, but is a more challenging environment in which to conduct geophysics and survey. We also have a great number of Sidescan sonar targets which have not yet been investigated, and we intend to continue to search these targets. If any dive clubs would like a list of target positions to dive on, you can contact CISMAS and we will provide you with a DVD containing Sidescan targets, images and positions. All we ask in return is that you let us know what you find.

A copy of the final project report is available free of charge both as a download and as a bound volume. For further information on how to request a free hard copy please see our publications page

The skipper, Bill Bowen, at the wheel The survey team and equipment

 

 

 

 

 

 

 

 

CISMAS