Jim Wallis wrote:

Apart from that you need to have confidence in your ability to navigate,
which in part at least means knowing what speed you can maintain for
that period.

The "where am I and where am I going?" aspects can be largely solved
with a GPS, but navigation also involves route planning aspects too, and
with a full tidal cycle that may well involve rather more than drawing a
straight line from one shore to the other! Speed, as Jim notes, will be
an important aspect of when you should be headed quite where. Merely
knowing where you are and where you want to go isn't the end of it.

Pete.
--
Peter Clinch University of Dundee
Tel 44 1382 660111 ext. 33637 Medical Physics, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net http://www.dundee.ac.uk/~pjclinch/