| English term or phrase: swimline | Hola a todos. ¿Serían tan amables de ayudarme con este término? Tomado de un libro de arqueología subacuática:
Swimline (freeline) searchesPractice, patience and perseverance are
prerequisites forthis method but it has been used with success on
manyarchaeological projects in the past. The system relies on a string of
divers, often between two and six, spacedalong a tape-measure or graduated
line at intervalsequivalent to less than the limit of clear visibility, so
thatcomplete coverage is possible (figure 12.2). The search is usually
undertaken with a ground-line to guide a con-troller. To enable positions of
objects to be fixed, it is useful also to graduate the ground-line in
convenientincrements. This technique is in fact a large-scale offsetsurvey
(see chapter 14). These ground-lines can be as long as necessary (up to a
kilometre has been known) and should be reasonably straight. To achieve this,
theyare probably best laid from a moving boat, keeping theground-line under
tension while it is being deployed. It can be difficult to lay long
ground-lines precisely, but with practice it is possible. As long as the line
is straight, the positions of the two ends can be fixed (seechapter 11) so
that there will be a record of where the searchtook place.The main difficulty
with this technique is maintainingthe line of divers at right angles to the
ground-line,which inevitably becomes more difficult in poor visibil-ity.
Another difficulty encountered with this method ismaintaining effective
communication between the diversto allow the line to advance smoothly. This
problemincreases proportionally to the number of divers on theline, and it is
also intensified by poor visibility. Usually,if a diver needs to stop to make
an observation, or is readyto move off again, this is indicated to the others
by a codeof signals along the line. With practice, it is possible
tocommunicate quite complicated messages along the con-necting line using a
set of bells (short tugs) and pulls (longtugs). Standard rope signals can be
found in many div-ing manuals and additional ones appropriate to the
individual operation can be devised.Another difficulty is the variation in
dive durationbetween individuals at the same depth and in the sameenvironment
caused by dissimilar equipment and breath-ing rates. Matching the contents of
the divers’ breathing-gas supply will help. It is considered best practice to
terminate the search when one of the divers needs to surface for whatever
reason, unless a buddy diver canaccompany the diver to the shore or
safety-boat.
Plotting the position of observations during the searchcan be achieved in the
same way as described when usingthe offset survey method. All that is
required is to recordthe distance along the ground-line and a distance out at
right-angles to the ground-line. To achieve a detailedsurvey two divers can
move slowly forward using a short rigid rule or tape, at right-angles to the
graduatedground-line (figure 12.3). Alternatively, markers can bedropped at
points of interest and the position fixed later.If the number of markers
needed by each diver is exces-sive, an alternative search method, such as the
jackstay system (see below) may be more suitable.Swimline searches are often
more effective in clear,shallow water, but this technique can be deployed
suc-cessfully in deeper water if consideration is given to usinga secondary
pair, or team, of divers to record the pointsof interest located by the
search team. With discipline, goodcommunication and rehearsed procedures this
techni-que can be very flexible, allowing the search-line to bestopped
periodically to record the nature of the sea-bed,or count the number of
surface-indicators (potsherds, forexample) to compile a distribution-map.
Muchas gracias de antemano.
Saludos. |
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