118 UNDERWATERSURVEY
- Expertise – what skills are available?
- Environment – what can actually be recorded?
- Funding – what funding is available?
Requirement: What needs to be recorded depends
on the aims laid out in the project design, which itself
should take account of the other factors listed here and
what information already exists (see chapter 5). For work
where no change to the site is being made, a varying degree
of recording can be considered because the work could
be repeated to a higher standard if required. Where
excavation is taking place, then ‘everything’ should be
recorded, to a level determined by the archaeological
director and set out clearly in the project design.
Time: How much can be recorded and the methods that
can be used are determined by the time available on site,
which itself depends on the time allocated to the project
and working conditions on the site. It is important to
plan how much time is likely to be spent working under
water, and how much time might be lost due to poor
weather or adverse tidal conditions. If working time is likely
to be short, then the aim should be to do a simple sur-
vey using simple techniques – a little useful data is much
better than no data at all. On average, it takes approx-
imately 5 minutes to make a single tape-measurement
under water. This time can be reduced or increased
depending on variables such as depth, size of site, tem-
perature, visibility, and experience.
Equipment: Most underwater survey methods use the
same basic tools: the tape-measure and drawing board.
Advanced tools such as acoustic positioning systems (see
below) are not commonly available but they are occasionally
used in support of underwater archaeological work and
so should be considered in the project planning phase. It
is important to ensure that the appropriate diving equip-
ment is chosen to enable the diver to carry out the work
safely and comfortably. A small rigid inflatable boat may
enable the project team to get to the site quickly but a larger,
hard-hulled boat may enable the team to spend all day
on site in comfort. The ability to process results on site
is a significant attraction of larger boats, as it allows for
the correction of mistakes and collection of additional
measurements there and then.
Expertise: It is essential to consider early in the project
whether or not the team has the appropriate archaeolo-
gical, surveying, and diving expertise to carry out the sur-
vey safely and accurately (see chapter 6). If additional skills
are needed, they are readily available in the form of
training, books, the internet, advice or recruitment of extra
team members. The Nautical Archaeology Society provides
training in many aspects of underwater archaeology to
a range of skill-levels. If any team member needs a
refresher, the survey techniques to be used can be prac-
tised on dry land beforehand.Environment: The location and conditions on the site
can limit how much can be recorded. Sites with features
scattered over a wide area are more difficult to survey accu-
rately. As a general rule, any group of features separated
by more than 30 m (98 ft) should be treated as a sep-
arate site. In good visibility, it is possible to position
control points further apart, therefore reducing the work
involved in setting up control. In very poor visibility,
there may be a limit to what divers can achieve (e.g.
checking that the tape is not snagged takes longer in poor
visibility). In strong currents the tape will bow, so con-
trol points will need to be located closer together to
reduce the length of each measurement. More points will
therefore be required to cover a site and survey work must
be scheduled around periods of slack water.Funding: Most of the limitations mentioned above can
be solved by spending more money. However, most
teams have a limited budget, which determines what
equipment can be used and how much time can be spent
on site. It should be remembered that an acceptable sur-
vey is normally achievable with limited resources.Setting Up a Baseline/Control Points
The basic principle of surveying is to be able to work out
the position of a survey point from some other point or
points, using known features to position the unknown ones.
On land the positions of known points are often provided
in the form of triangulation or ‘trig’ pillars, unfortu-
nately these do not exist under water so they must be cre-
ated. To start a survey, all that is required is to measure
the distance between two primary survey points on the
site. As yet, the location of the two primary survey points
in the real world is not known. They are assigned arbi-
trary coordinates so they can be drawn (to scale) on a plan.
These two points are now ‘known’ control points; with a
‘baseline’ drawn between them, they form the start of a
site-plan. By measuring the distances and/or angles from
both these points to other fixed points on the site, the other
points can be plotted relative to the two initial control
points on the plan. It is then possible to draw up a net-
work of survey-points joined by distance measurements.
The site-plan of points and distances is drawn to scale and
represents the archaeological site lying on the sea-bed.
Most archaeological sites will require more than two con-
trol points, which will form a control point network.
These points are the framework on which subsequent
survey work is built. Permanent, fixed points are placed