Monthly Archives: May 2011

Introduction to Navigation Part 5 Understanding Latitude and Longitude

Finding a street address on earth is not a difficult task, however finding a specific location in the middle of the ocean can present the mariner with a few problems.  In order to locate a specific location anywhere on earth, a grid system has been developed to give each area on the earth a specific address.  This system deals with “parallels of latitude” and “meridians of longitude.”

In order to begin to understand how to navigate, the navigator must understand some basic terminology and how it relates to the grid system.

These basics are covered in the online Nautical Know How Basic Boating Safety Course at http://boatsafe.com/navigation . It is highly recommended that, prior to beginning this advanced Coastal Navigation Course, each student successfully complete the Basic Boating Safety Course.

 A “great circle” is a circle formed on a sphere, such as the earth, by the intersection of a plane passing through the center of the sphere.  An arc of a great circle is the shortest distance between two points, hence a great circle route is the shortest route between two points on the earth.  You might think of splitting an orange down the middle and going through the center.  The plane exposed would represent a great circle.

 A “small circle” is a circle formed on a sphere, such as the earth, where the intersection of a plane does not pass through the center of the sphere.  Cut that same orange in any other manner that does not pass through the center and you have created a small circle.

Parallels of Latitude are small circles that are measured from the equator (the only latitude that is a great circle) beginning at O° latitude at the equator to 90° North and South at the Poles.  These parallels are equal distance apart and run horizontally across a chart, like the rungs on a ladder.  You can use the “ladder” analogy to remember that “laddertude” lines are drawn across the chart, not up and down. 

Because latitude lines are equal distance apart they can be used to measure distance on the surface of the earth.  The only parallel of latitude that is a “great circle” is the equator itself as shown in the graphic. You will find latitude measurements on the side of your nautical chart.

Meridians of Longitude are “great circles” that pass through the north and south geographic poles.  The meridian of longitude that cuts through the earth at Greenwich, England is labeled as O° longitude and is known as the prime meridian.  Longitude is then measured from O° at Greenwich to 180° West and 180° East of Greenwich. The 180°th of longitude is the International Dateline.

Related Posts:

https://boatsafe.wordpress.com/2011/05/17/introduction-to-navigation-part-4-getting-to-know-your-magnetic-compass/

https://boatsafe.wordpress.com/2011/05/16/introduction-to-navigation-part-3-definitions/

https://boatsafe.wordpress.com/2011/05/13/introduction-to-navigation-part-2-nautical-charts/

https://boatsafe.wordpress.com/2011/05/12/introduction-to-navigation/

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Introduction to Navigation Part 4 Getting to Know Your Magnetic Compass

You may have noticed, if you have looked at a nautical chart, that there were two rings on the compass rose. The outside ring is based on true north and the 000° direction points to the true North Pole. On the inside ring labeled “MAGNETIC” the  000° direction points in a different direction than the outside ring.

These basics are covered in the online Nautical Know How Basic Boating Safety Course at http://boatsafe.com/navigation . It is highly recommended that, prior to beginning this advanced Coastal Navigation Course, each student successfully complete the Basic Boating Safety Course.

The difference between True and Magnetic is called “Variation.” Variation is a naturally occurring disturbance caused by the magnetic north pole. Variation will change depending on where you are located on the earth. If you are operating on the West Coast of the US you will have east variation because the magnetic north pole is located east of you. On the East Coast of the US you have west variation because the magnetic north pole is west of your location.

Another error which may show up in your magnetic compass is called “Deviation.”  Magnetic compasses are also affected by magnetic fields on the vessel itself. Just put some sort of ferrous metal such as a screw driver next to your compass and you will see an example of this error.

Significant errors of deviation could be caused by metal tanks, your engine, metallic objects near your compass or even electromagnetic interference caused by your radio.

To safely and accurately navigate from one position to another it is important to be able to correct for both “variation” and “deviation”  and be able to steer a course by your magnetic compass.

If you want to learn more about the magnetic compass and how to calculate TVMDC…READ MORE.

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Introduction to Navigation Part 3 Definitions

The following navigation terms are used in most recognized navigational texts. Learning and understanding what they mean will give you a head start on the information that is to be presented in later chapters. Don’t worry about memorizing all these at this time. You will get plenty of exposure to these terms as you advance through the course.

These basics are covered in the online Nautical Know How Basic Boating Safety Course at http://boatsafe.com/navigation . It is highly recommended that, prior to beginning this advanced Coastal Navigation Course, each student successfully complete the Basic Boating Safety Course.

Piloting is defined as the determination of the position and the direction of the movements of a vessel. This involves frequent or continuous reference to landmarks, aids to navigation, and depth sounding.

Direction is the orientation of an imaginary line joining one point to another without regard to the distance between them. Direction is measured in angular units of arc, measured in degrees, from a common reference whether it be true north or magnetic north. The usual reference is true north. The division of the degree may be either minutes and seconds or decimal fractions. Direction is written with three digits as in 000°.

Distance is the separation between two points without regard to direction. In navigation it is measured by the length of a line on the surface of the earth from one point to the other. It may be measured in units of yards, nautical miles or kilometers. The nautical mile is commonly used by navigators. The international nautical mile is 6076.12 feet. This is approximately 1.15 longer than the statute mile used on land.

Time is written as four digits in a 24 hour system; four minutes after midnight is 0004, 9:32 AM would be written as 0932 and 1:16 PM would be written as 1316.

Speed is defined as the rate of movement, and in navigation is usually measured in nautical miles per hour, or knots. The time element is included in the definition of “knot”; the use of knots (kts) per hour is incorrect. Speed is represented on your chart as “S”. Example S = 7.5 kts.

Dead Reckoning (DR) is the projection of a present position to an anticipated future position. This is done by using a previous known position and applying known direction, speed and distance covered. The term comes from deduced reckoning which was abbreviated ded reckoning. DR plots are done at a minimum of every hour or when ever you change course or speed. A new DR plot line is started each time a new “known position” is found.

Course is the direction of travel through the water or the direction a vessel is to be steered or is being steered. The course may be designated as true (T), magnetic (M), or compass (C). Course is always written in three digits and is followed by the abbreviation of its source. Example C = 090° T

Bearing is the direction of any place or object from a given point. It may be designated as true (T), magnetic (M), compass (C) or relative (R). It is always written in three digits and is followed by the abbreviation of its source. Example B = 270° T

Heading is the direction the vessel points or heads at any instant as read from your compass. It is always written in three digits. Example HDG = 270°

Fix is a known location at a specific time based on verifiable information and carrying a high degree of accuracy. Example:  0900

Running Fix is a known location at a specific time, with a lesser degree of accuracy than a fix. It is based on information obtained from a single event at two different times and plotted as a common time. Example:  R Fix 0900

Electronic Fix is a fix obtained from one or more electronic devices. Example:  0900

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Introduction to Navigation Part 2 Nautical Charts

Today is the second of a series of articles about Navigation. You can advance your Navigation Know How by participating in the Nautical Know How Coastal Navigation Course.

These basics are covered in the online Nautical Know How Basic Boating Safety Course at http://boatsafe.com/navigation . It is highly recommended that, prior to beginning this advanced Coastal Navigation Course, each student successfully complete the Basic Boating Safety Course.

Nautical charts are different from maps in that they specifically depict water areas while maps concentrate on land area, roads, landmarks, etc. Land areas and features on charts are sketchy and are noted only for their interest to the Navigator. Unlike maps, the nautical chart conveys much information specifically designed to assist in safely navigating the area that the chart covers.

Chart Scaling

 The scale of a chart is expressed as a ratio such as 1:80,000. This could also be represented as the fraction 1/80,000. This means that one unit on the chart represents 80,000 of the same units on the earth. The terms “small scale” and “large scale” can be confusing if you haven’t studied fractions recently. The denominator of the fraction (the number under the line) is the number that changes as the scale of the chart changes. The larger the denominator  the smaller the fraction. For instance 1:80,000 is smaller than 1:40,000, so the larger the denominator the smaller the scale of the chart. That is, a 1:80,000 chart would be a small scale while a 1:40,000 would be a large scale.

 Chart Colors

The major water areas are not colored and retain the white color of the paper itself. Shallow water areas, shown in light blue and light green, indicate shallows that are uncovered at some stage of the tide, such as marsh areas.

 Small objects such as buoys and markers are shown in a magenta color. Because charts are used at night under red light (to keep from impairing night vision) the color magenta shows up best at night and in the day.

 Buoys and dayboards that are actually red are indicated in magenta. Green buoys and dayboards are shown in green.

Lighted buoys, regardless of their color, are shown with a magenta dot over the small circle portion of the chart symbol. Cautions, symbols noting danger, compass roses and recommended courses are also noted in magenta.

For more about the Nautical Know How Coastal Navigation Course…READ MORE.

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Introduction to Navigation

Today starts a series of articles about Navigation. We will give you a list of skill sets required to become a “real” navigator and also give you the opportunity to advance your Navigation Know How by participating in the Nautical Know How Coastal Navigation Course. This course will give you step-by-step instructions on how to navigate safely from one point to another. It teaches you to take into consideration all effects including set, drift, tides, currents, etc. that might hinder you along the way.

These basics are covered in the online Nautical Know How Basic Boating Safety Course at http://boatsafe.com/navigation . It is highly recommended that, prior to beginning this advanced Coastal Navigation Course, each student successfully complete the Basic Boating Safety Course.

Navigation can be divided into four primary classifications:

  • piloting
  • dead reckoning
  • electronic navigation
  • celestial navigation

The problems that you, as a navigator, must solve are as follows:

  1. How to determine your position.
  2. How to determine the direction in which to proceed to get from one position to another.
  3. How to determine distance and related factors of time and speed as you proceed.

Of these three problems facing every navigator, the most basic is that of locating your position. Unless you know your position, you cannot direct the movements of your vessel with any accuracy, safety or efficiency.

You will need to have, and learn to use, several navigation tools. Although there are many tools at your disposal at any marine store, the following are the minimum necessary:

  •  dividers
  • parallel rulers
  • right angle triangle (optional, but handy)
  • charts
  • pencils
  • hand bearing compass
  • steering compass
  • watch or chronometer
  • log and time-keeping note paper
  • calculator, abacus or fingers & toes

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The Other Top Ten Boat Names

Just a few weeks after FirstBoat announced the most popular boat names of 2011 (view FirstBoat’s top boat names here), BoatU.S. has released their version of the top ten boat names based on their own data.

There are some similarities between the two lists, and of course there are some differences. The similarities include the way the data was gathered, as well as the fact that three names made it to both lists this year (Could those three names be the most definitive top three boat names ever?)  Differences include the breadth of data each company uses to create their list of top boat names.

Boat US?
That’s right –  in addition to selling insurance, towing services, marine products, etc., BoatU.S. also sells vinyl boat lettering. To come up with their list, they scan the boat names that their customers order throughout the year when customers make their purchases. This is not too different to how First Boat arrived at its top boat names. The FirstBoat list is compiled based on the most frequent unique purchases of vinyl boat lettering at CustomBoatNames.com, and unique purchases of personalized boating gear and apparel from BoatNameGear.com. Of course, no personal data was shared with anybody, ever, as we’re sure is the case with BoatU.S. as well.

Their Top 10 Boat Names
Anyway, you probably only care about the top 10 boat names, so here are the top ten from BoatU.S.

  1. AquaHolic
  2. Andiamo(Let’s go)
  3. The Black Pearl
  4. La Belle Vita(The Beautiful Life)
  5. Mojo
  6. Island Time
  7. Second Wind
  8. No Worries
  9. Serenity
  10. Blue Moon

The Ultimate Top 3 Boat Names?
Boat names that made it to the BoatUS list as well as to FirstBoat’s top ten include:

Andiamo (7 at FirstBoat)
Black Pearl (6 at FirstBoat)
Serenity (1 at FirstBoat)

Those three boat names are the only ones to appear on both lists, which derive their results from different sources. Does that make “Serenity”, “Black Pearl” and “Andiamo” the three definitive most popular boat names overall?  What do you see around your dock?

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Ways to Save on the Water this Summer

Fuel nozzleWith the ever spiraling cost of fuel for your boat, here are a few tips on how you can save. I know, the news has been reporting that prices should be going down but as was noted by Jay Leno last Friday, “The price of oil is now under $100 a barrel. The oil companies say they should be passing on the savings to us in six or seven years.”

Tips For Reducing Fuel Usage:

  • Slower speeds on the water will reduce use.
  • The proper use of trim tabs reduces drag, especially while accelerating up to planning speeds.
  • Minimize the amount of time that you idle at the dock.
  • Minimize the use of onboard generators.
  • Use dock-side electrical power in lieu of generators.
  • Have a float plan so you know exactly where you’re going.
  • Make sure the hull is clean.
  • Don’t under-power your boat. It’s important you have enough motor to handle the load.
  • Check your propeller. If your boat is slow “out of the hole” (getting up on plane) or lacks top-end speed, you might have the wrong propeller.
  • A well-tuned engine uses less fuel.
  • Use the grade of gasoline specified by the engine manufacturer.

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