The underwater excavation of a wreck follows several stages.
A preliminary survey can give us an idea of the date and origin of the wreck.
It is from these data that the justification of an excavation could be given
and that research objectives can be defined.
Before undertaking an excavation, the first stage is to perform
a basic survey in order to determine the ascendancy of the wreck and if possible
its orientation in space.
If such crucial data as the ship's environment, research objectives, and the
general position of the wreck can be defined, an excavation strategy can be
developed as well as the extent of the work, the work procedures and the respective
stages in order to achieve the goal.
1 - Installation of a location
system
2 - Clearing away of the
sediment
The removal of the sediment must be carried out in successive horizontal layers. It is indeed the most effective way to understand the structures and to preserve the objects that appear. The beginning of the removal is one of the most delicate phases of the excavation since one does not know what he is going to find and also due to the fact that the first structures to appear are generally decayed and thus the most fragile. The destruction of these first discoveries can be a great loss to the operation, contrary to well-preserved structures which are easier to understand. During this phase the discovered objects are taken according to methods which must be defined in advance according to their nature. The most fragile objects such as organic matter and ferrous concretions can be taken only after examination of their positioning. Before removal, certain objects must be numbered and if needed they are photographed on site and a partial listing is done. |
3 - Study of the structures
The structures must then be identified and marked.
They are then measured one by one in order to reconstitute their form. A series
of accumulated measurements must make it possible to recreate the function
of each item or element as a whole. Particular care is taken to the study
of the assemblages such as the shaping of wood and the use of nails or pegs.
Certain structural elements will have to be momentarily surfaced in order
to be photographed and drawn.
The cutting and disassembly of some structures will be necessary to reach
inaccessible parts of the site.
The reconstitution of the forms will be possible by cross-referencing information
gathered from several types of measurements:
- cross sections are situated accordingly, with respect to the longitudinal
axis of the wreck,
- photogrammetric listings which will allow a three dimensional reconstitution.
All of the measurements taken will allow for to the preparation
of individual maps, overview maps, and then instructional maps for the restoration
of the structures (axonometric reconstitutions for example).
Models taking into account the archaeological data must allow for the study
of the hull according to the pre-established research axes and lead to the
completion of overall reconstitution models.
4 - Collection of archaeological
artefacts
The found objects will be indexed while at the same time keeping in memory
their position on the site. If necessary they will undergo a preliminary preventive
conservation procedure: for example rinsing and desalting ceramic objects,
conditioning the organic matter, conserving the wooden objects in fresh water
containing fungicide. The objects will then be dealt with by a laboratory
specialized in the conservation of archaeological artefacts obtained from
underwater excavations.
©
Max Guérout