Wednesday 3 September 2008

Dive site mapping

The role of a dive leader demands knowledge of dive sites as well as the use of dive site maps when conducting a pre-dive briefing. This knowledge should include layout, distances, depths, entry and exit points as well as any possible currents and hazards. Safety is an important factor but having a map will allow divers to visit the best features of the site by marking where they are and what to look out for.

One of the easiest ways to map a dive site is to use a large slate, tape measure, compass, depth gauge and fixed buoy in order to create an accurate picture of the underwater terrain.

Large slate: If possible use one with pre-printed grid markings.

Tape measure: purchase a 30m reel from your local hardware store.

Compass: use a compass to draw intersecting distance arcs.

Secure buoy: use as a central point from which everything is to be measured.

Using this technique

(1) Start by drawing a quick sketch of the site from memory on a slate - it's a good base from which to add measurements and bearings and will help you set parameters.

(2) Select a central point from which everything on the site will be measured (setting up a buoy will allow you to attach a reel to measure distance)

(3) From the central point swim using a U search pattern as it a good way of covering a large area.

(4) Use kick cycles to measure distances between each feature. Find out how many kick cycles it takes you to fin from one end of a 10 meter line to the other. Use this number to convert kick cycles to meters when moving from one feature to the next, noting distance and depth.

(5) Take a bearing from each feature, again from the central point. Mark these on the rough sketch.

(6) Note features as not-to-be missed areas of the dive as well as of any potential hazards. Note entry points for both boat and shore diving.

(7) If drawing to scale you'll need grid paper, protractors and rulers. This will highlight areas that may need to be surveyed if they don't match up correctly.

(8) Note the depths to the bottom if known (make a note after every 5 meters or so) - this helps create contour lines on your final version.

(9) Add relevant topside features (car park, evacuation area, as well as where oxygen and first aid kit is positioned).