90 seamanship secrets
and compare the estimates with the actual distances run (over ground) as
reported by your GPS receiver. One day, when GPS isn’t working, this practice
estimating boatspeed in various conditions of wind, waves, and current will
prove valuable.
Make a GPS Grid Highway to Avoid Dangers
Use the latitude and longitude function on any GPS receiver to keep your
crew safe and sound. This also works when using an unfamiliar GPS receiver.
This method quickly shows your advance along a track and whether you are
drifting toward danger.
For example, you need to clear a dangerous ledge off your port bow. Pea
soup fog has reduced visibility to a couple of hundred yards. Follow these steps
for safety.
- Plot your TR on the nautical chart. Draw the dead reckoning courseline
of your approach onto the chart, then plot a turn to due north or due south
when you near the ledge but are still safely off it. Th is north-south trackline
marks the center of the grid highway you will use to avoid the danger.
Power or sailing vessels should plot the same base courselines. (We’ll talk
about tacking strategies shortly.) - Make the sides of the highway. Determine how closely you are willing
to approach the ledge. Th is minimum distance east or west of the ledge
establishes one edge of the grid highway you are creating; draw a vertical
line (i.e., a meridian) through that point, extending it so as to clear the
danger both north and south. Label it with the longitude in degrees and
minutes. Draw a second meridian on the opposite side of the north-south
trackline you plotted, thus defi ning the width of the “road” you desire to
stay on. Power and sailing vessels simply need to stay between the two
meridians in order to pass the hazard safely. - Make the entry and exit gate. Well north and south of the hazard area,
draw in two parallels of latitude. Th ese defi ne the entry point into the
hazard area and the exit point when you are clear of the hazard.
TACKING THROUGH THE HIGHWAY
Sailing vessels hard on the wind will need to tack through the grid highway.
In the illustration, the vessel enters the gate on starboard tack and sails until
the GPS reads 71o54'W. The boat then comes about onto port tack and sails
until the GPS reads 71o53'W. Then the boat comes about again, repeating the
sequence up the highway until the GPS latitude reads 42o19'N.