Equipment:
Underwater navigation requires little extra in terms of
equipment. Some types of navigation can be done without anything more
then basic SCUBA equipment. But most underwater navigation requires
an underwater compass (~$70). Compasses can be mounted on a wrist, on
the SPG, or on a slate. When mounting a compass make sure it is
mobile enough that you can easily view it while swimming. Several
other items can be of use. Here's a brief list and description of all
the major items useful for underwater navigation:
Compass:
An underwater compass is central to navigating underwater. Compasses
work by detecting the earths magnetic north pole. Like all compasses
underwater compasses contain a magnetized needle which always points
towards the magnetic north pole. Underwater compasses are contained
in a waterproof case, and often have a rotating bezel which is used to
take bearings. Underwater compasses come in two types, direct reading
compasses and indirect reading compasses. A direct reading compass
has the bearings written on the magnetic disk. To determine what
direction you are heading in you look in a small window on the compass
- you can directly read your bearing off of the disk. Indirect
compasses have bearings marked on a bezel, and a floating magnetic
needle in place of the magnetic disk. These compasses are a little
harder to use as you must set the bearing you wish to travel on the
bezel, ad then align the needle with north. However, these compasses
are better for taking bearings to objects, which is very useful while
mapping.
The use and advantage/disadvantages of both types of
compasses is covered in detail in the basics
page.
Slate:
Another useful item is a writing slate. This is simply a rough piece
of plastic which you can write on underwater with a pencil. Slates are
useful because you can write down your dive plan before you dive (good
if you have a bad memory). They can also be used to keep track of
measurement you take while diving, or to take notes about the dive.
Land Compass:
Land compasses are more accurate then diving compasses for taking
bearings to object. Unfortunately they cannot be used underwater, but
they can be used to plot the locations of dive sites from shore. For
more on this see our mapping section.
GPS:
GPS units can be used from a boat to get an extremely accurate
location of a dive site. GPS units use signals from satellites to
mark your location on the earth to within 10m (30'). This can be
useful for marking the location of a dive site, or for mapping dive
sites. Unfortunately, there are GPS units which divers can carry -
the water pressure would crush most units. And even if one was made
that could stand the pressure it still wouldn't work, as the signals
from the satellites cannot penetrate water. Even so, GPS units play a
central role in getting dive boats to dive sites.
Buoy's:
Marking buoy's are useful for mapping the location of dive site. Some
buoy's have permanent buoy's attached to them. You can attach a buoy
to a dive site so you can map it from shore. A variety of buoys are
available - you can use your dive flag as a buoy, commercially made
marker buoy's are available. Even a milk jug or large pop bottle
attached to a rope can make an excellent buoy.
Other Items:
The above items are all that most people will need. However, for
mapping dive sites you may need additional equipment, including
baselines, tape measures, and other items. These items are covered in
detail in the high accuracy mapping page.
