Nautical Charts

There is a difference between the terms "map" and "chart." A map shows land areas. It also shows the physical features of the land, cities, towns, roads, political boundaries, and other geographic information. A chart, specifically a nautical chart, shows primarily areas of navigable waters. It also shows coastlines and harbors, depths of water, aids to navigation, channels, and obstructions. A chart provides a means of describing position in terms of latitude and longitude.

 

Latitude is a measurement of Distance

1Degree of Latitude = 60 nm

1 minute of Latitude = 1 nm

1 nm = 2000 yds = 6000 ft = 1.136 statute miles

 

Longitude is a measurement of Time

15 degrees of Longitude = 1 hour

Greenwich mean Time is the Zero meridian (UTC or Zulu Time)

The international date line is 180 degrees after/before the 0 degrees meridian

180 degrees = 12 hours (1/2 way round the Earth AND ½ way through the day) The date changes at 180 degrees.  All longitude are read as either east or west of the prime meridian, example:  Moscow, Russia approx 037 degrees East, New York is approx 074 degree West.

 

 

Most of us will use nautical charts created by Mercator projection, common for inland and coastal navigation.  The nautical chart is a two dimensional image of Earth’s surface. Transferring the information from a round surface to a flat representation is called a projection.  This results in various distortions, but as long as two requirements are met we can use this image for navigational purposes. First, the angles are true representations of actual angles between the real objects, which they represent. Second, a straight course should appear as a straight line on the chart.

 

The Mercator projection fulfills these requirements with parallels & meridians, which are straight and parallel; the meridians & parallels will be perpendicular to each other.

 

 The Mercator projection is constructed by wrapping a cylinder around the planet so that it touches the equator. On this cylinder the surface of the earth is projected and finally the cylinder is cut open to yield our chart. But where the meridians converge on the globe they run parallel in the projection, indicating the distortion. Look, for example, at a high parallel. The length of such a parallel on the globe is much smaller than the equator. Yet, on the chart they have exactly the same length creating a distortion, which gets bigger nearer to the poles.  To compensate for this distortion, measurements of distance on a Mercator chart are always measured along Lines of Latitude closest to the object or area being measured.

 

 

BASIC INFORMATION SHOWN ON CHART

The chart’s legend will show the title of the chart, which describes the waters covered; type of projection used; the scale; unit of measurement used for water depths (feet, fathoms, or meters); and the datum plane for the soundings.

 

Also on the chart (where space is available) other useful information can be listed. This information could include the meanings to special abbreviations, cautions, special markings, and any other information that may be of value to the mariners. Boxes and notes may be printed in the margins or on the face of the chart at locations where it will not block out other navigational information.

 

EDITIONS AND REVISIONS

The edition number and the date of the last revision will always appear in the lower, left-hand corner of the chart along with the chart number.

 

COLOR AND LETTERING

Land areas are shown in a buff or yellowish color. On DMAHTC charts, land areas are shown in a gray tint. Shallow or shoal waters are shown in blue, and deep-water areas are shown in white. Areas that may be submerged at some tidal stage, such as sandbars, mud flats, and marshes are shown in green. The color "magenta" is used for most information listed on the chart because it is easier to read under red nightlights.

 

By knowing the type of lettering being used, you can more easily and quickly interpret the type of information being presented.

 

Upright or Roman Lettering - Identifies features that are dry at high water.

 

Slanting or Italic Lettering - Identifies submerged or floating hydrographic features (this does not include sounding figures, showing depth).

   

You should have a copy of Chart 1, handy at your Nav Station.  This is the key for all symbols and abbreviations used on the chart. 

 

Chart Corrections

In a perfect world you should check your weekly Notice to mariners and make chart corrections on your charts.  I highly recommend that you periodically review and correct you charts through out the season and definitely before entering unfamiliar waters or areas which you have not cruised recently. 

 

At the beginning of the boating season, it may be prudent to purchase POD  (Print on Demand) charts which are corrected to time of printing (when ordered), especially for high traffic and areas of multiple corrections.

 

 

CHART BOOKS & GUIDES

Chart Books and cruising guides, remember that chart books and cruising guides have not been corrected to recent Notice To Mariners.  Same may be true for digital charts!  Some digital chart providers, such as Maptech and Nobeltec, offer update service for their digital charts.  I always recommend that you print a copy of the corrections from your local notice to mariners for any charts in your operating area.  Review them each cruise.  Make corrections and notes (temporary operating area activity and restrictions, fishing notices, etc) on your paper chart as a reference along with your electronic chart plotter!  The suspenders and belt system may keep you safe and worry free.

 

 

FREE UPDATED DIGITAL NOAA CHARTS

Another item of interest – Free Digital and Vector Charts!  You may download updated digital Raster (RNC) and Vector (ENC) directly from NOAA .

Raster Charts -   http://nauticalcharts.noaa.gov/mcd/Raster/Index.htm

Vector Charts - http://www.nauticalcharts.noaa.gov/MCD/enc/index.htm   

 

As the new boating season begins, please Take a little time to review you navigation charts and publications.  Update as required, get you current Notice to mariner, tide & current tables, look over the rules of the road and enjoy a safe boating season!

Determining the Ship’s Position Using Horizontal Sextant Angles

 

Horizontal  sextant  angles  give fixes of great accuracy that are  not affected  by  any  error  of  the  compass.  A  fix  by  horizontal  sextant  angles is  labeled  the  same  as  a  visual  fix  with  a  small  circle  around  the  position and  the  time  of  the  fix  close  to  the  fix  symbol.

 

Horizontal  sextant  angles  used  in  conjunction  with  a  computer-assisted positioning  program  are  the  most  common  method  used  by  the  Coast Guard  to  position  aids  to  navigation.

 

Horizontal  sextant  angles  should  be  taken  as  nearly  simultaneously  as possible,  preferably  by  two  people  on  a  predetermined  signal.  However, one  person  can  obtain  both  angles  if  the  ship  is  not  moving  quickly.

 

To  obtain  a  fix  using  sextant  angles,  you  must  have  three  fixed visual  objects,  and  those  objects  must  be  identifiable  on  the  chart.

 

Follow  these  steps  to  obtain  horizontal  sextant  angles:

 

1.  Hold  the  sextant  horizontally  with  your  right  hand.

 

2.  View  the  left  object  directly  through  the  telescope.

 

3.  Release  the  index  arm  with  your  left  hand  on  the  release levers  and

     swing  the  arm  so  that  the  index  mirror  reflects  the center  object  in  the

     horizon  glass  below  the  left  object.

4.  Rotate  the  micrometer  drum  to  fine  adjust  the  reflected object  in  line

     with  the  object  viewed  directly.

 

5. Take  a  reading  of  the  angle.

 

1. Do  you  have  two  people  taking  angles?

 

Ø      If  yes,  both  angles  are  ready to  be  plotted.

Ø      If  no,  repeat  steps  1  through  5  using  the  center  object

                   viewed directly  and  the  right  object  viewed  reflected.

 

 

Now, select three objects which are on your chart and in sight.  Measure the angle on each side of the middle object (which is common to both angles).

See illustration below…

 

 

Taking angular measurement with Sextant

 

Using the Three-Arm Protractor

 

The  two  angles  measured  are  plotted  using  a  three-arm  protractor.  This instrument,  made  of  brass  or  plastic,  consists  of  a  circular  scale  that  can be  read  to  fractions  of  a  degree  or  minutes  of  arc,  and  to  which  the  three arms  are  attached.  The  center,  or  index  arm,  is  fixed  and  the  zero graduation  of  the  protractor  coincides  with  the  straightedge  of  this  arm. The  other  arms  are  movable  and  can  be  set  and  locked  at  any  angle relative  to  the  fixed  arm.

 

The center arm is placed on the center object of your sights, with corresponding arms on the object to the left and the right set at ANGLES read from sextant.

The pivot point (center of protractor) is the resulting position at the time of the sights.

If  the  three  objects  and  the  ship  all  lie  on  the  circumference  of  a  circle, the  fix  is  NOT  reliable.  When  this  happens,  it  is  called  a  swinger  or revolver  and  your  ship  could  be  anywhere  along  the  circle  and  still  have the  same  two  angles  to  the  three  objects.

Procedure for Plotting the Fix

1. Place  the  three-arm  protractor  on  the  chart.

 

2. Position  the  center  (fixed)  index  line  so  that  it  passes  through the  center  object.

 

3. Move  the  protractor  slowly  across  the  chart  until  all  three  arms are  aligned  with  the  three  objects.

 

4. Mark  the  ship’s  position  on  the  chart  by  inserting  a  pencil point  in  the  center  of  the  protractor  (pivot  point).

 

5. Check  to  see  that  the  fix  is  not  a  swinger  or  revolver.

 

This method using a sextant for Coastal & Inland navigation can be more accurate than GPS!

Yelapa, Mexico – off the hook!

 

Sometimes during a long passage, you want a vacation from the boat!  The mantra “A palapa in Yelapa beats a condo in Redondo” advertises the perfect get-a-way during your voyage.  Now don’t get me wrong, I love boating, I have sailed all around the world, literally!  But I do appreciate the joy of a quiet out of the way refuse near the sea.

 

While there is anchorage available in Yelapa, due to deep water, irregular bottom and exposure to the northwest swell and shifting winds, Puerto Vallarta provides safe and secure moorage only 14 ½ miles away.  You can take your tender (depending on size and comfort) or a water taxi (Cost $11 each way – don’t buy a round trip ticket) for the short trip across Bahia Banderas.  You will rest and enjoy the stay without worry as your yacht rests safely and secure back at the marina.

 

If you decide to anchor in Yelapa, you will need a bow and stern anchor, due to the shifting winds and nearby pangas.  As you enter the bay, a couple pangas may meet you offering mooring.  I suggest this is a good deal, usually around 200 Peso - $20 bucks!  They will assist you to a safe mooring, assist in placing and taking in your stern anchor, plus provide shuttle service to the nearby beach.  If you chose to go it alone, the best places (marked above) are in 25 to 50 ft water.  Remember, pangas have a right of way here – use caution!

 

 

Yelapa

 Yelapa is a quiet village only accessible by the sea.  The only motorized vehicles are a few ATV’s and Motorcycles (off road).  The main transportation is by boat, mule, horse and foot.

 

The people are friendly and very helpful when approached.  If you wish to be left alone, they respect that as well.  The food is wonderful in and around the village; the main beach palapa food is a little overpriced and served to tourist who come over on the "day boats" from PV (Puerto Vallarta).

 

 

Behind the beach restaurants, where the horses hang out, there is path from the big beach which will lead you through the jungle along the river and past working ranches and the Yelapa primary school to El Manguito.  One of the most moderately priced restaurants in Yelapa offering good, fresh food, and excellent margaritas. As the proprietor exclaimed, we are always open, “See – no doors” as he motioned around to the open air restaurant!

 

Many of the restaurants are off the main path, but worth seeking out, such as the Passion Flower Gardens, which serves home style American dinner and movies Monday evenings and Italian food from 6 to 9 pm on Thursday nights.   The best way to find out about these gems is to ask the locals and check out the posters stapled to the utility poles in the village!

 

Our Palapa in Yelapa

I believe my wife had chosen this palapa to force me into the dreaded event – exercise!  We hiked along the shore from town past numerous palapas along the beach, suddenly we have left the lapping surf behind  as we climbed the hill to the highest palapa in Yelapa!  After 325 steps and countless switchbacks and one climate change we reached our home for the week!  And it was worth every step!!!

 

 

Our palapa was actually two separate thatched roof buildings. The main house had a roomy kitchen, refrigerator, sink, gas stove and oven with a counter bar separating the lower bedroom. 1 queen sized hanging bed and a single daybed both with mosquito netting enclosure.

 

 

The next building had the bathroom, looking out over the bay (as did the open air shower).  Upstairs of each building had a loft bedroom, both with queen beds).  Hammocks and chairs faced the spectacular view of the bay!

 

 

From out perch on the hill, we watched whales and boats travel past as  birds raced by.  It was worth every step to live on the front stoop of heaven!

 

Provisioning is easy, shops in village always seem to be open, banana trees at your door step along with lemon trees all around.  Don’t forget the beach, fishing is incredible! 

 

 

I thought that a week in this paradise would find me wanting to get back to the sea, but I must admit for the first time in my life, this was a vacation which I wish had no end.

 

end.