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Introduction to Navigation Part 6 Time Calculations

Navigation uses the 24-hour clock as its standard.  If you were fortunate enough to have been in the military, you probably are familiar with the 24-hour clock or military time.  However, if it has been a while since you have done anything except look at the numbers on your digital wristwatch you may need to brush up.  All time used in navigation is expressed as four digits.  The first two digits are the hour number.  The second two numbers are the minutes. Starting with 0000 hours at midnight, the hours are counted as 0100, 0200, 0300, etc. through 1200 at noon.  After the noon hour the hourly intervals continue to count with 1300 (1:00 PM), 1400 (2:00 PM), etc. until you reach midnight (0000) again.

Minutes are indicated with a two-digit number after the hour interval.  For example, 8:30 AM is written as 0830, and 12 minutes past four o’clock in the afternoon would be written as 1612.  Using military time there is no need to use AM or PM.  A time of 0900 is nine hours after midnight (9:00 AM), and 9:00 PM would be written as 2100 (9 hours past 1200).

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.

Calculating Time

The 24 hour clock makes it easy when you have to add or subtract time, one of the essential parts of doing distance, speed, time calculations.  Obviously, if you need to know how far you have gone at a certain speed you need to know how long (in time) you have been traveling.

As an example, if you wanted to find the time interval between a departure time of 0915 and an arrival time of 1325, you could set up a simple subtraction problem.    Hr
   13
 -09
  4 Hr
Min
25
15
10 Min 
Some problems can become a little more complex than the straight-forward subtraction problem above. What if you needed to find the time interval between your departure of 1345 and your arrival at 1515? When you set up the problem you get an unusual looking situation.    Hr
   15
  -13
    ?
 Min
15
45
? Min
 
You should remember that the two sets of two digit numbers represent two different units, i.e. hours and minutes. Just like in regular math, you must subtract the units to the right before you can subtract the units to the left.  In this case you have to borrow an hour from the hours unit.  Converting the hour to minutes, you have borrowed 60 minutes. So, 1515 is rewritten as 1475.
 
   Hr
  
15
   14
  -13
   1 Hr
 
Min
15
75
45
30 Min

Once you have properly set up the problem by borrowing an hour and converting to minutes, you simply perform a standard subtraction by taking 45 minutes from 75 minutes and 13 hours from 14 hours.  You time underway equals 1 hour and 30 minutes.

Related Posts:

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

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

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

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

https://boatsafe.wordpress.com/2011/05/18/introduction-to-navigation-part-5-understanding-latitude-and-longitude/

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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 . 

 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 .

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 Coastal Navigation  Course at http://boatsafe.com/navigation .

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 .

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

Gay Head LightToday 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 . 

ORDER BY DECEMBER 20 FOR ARRIVAL BY CHRISTMAS.

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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Have the Water to Yourself – Enjoy Off-Season Boating

Submitted by John M. Malatak, chief, program operations, U.S. Coast Guard, Boating Safety Division.boating-in-the-fall

I love boating in the fall. The waterways that bustle with activity in the summer often have a different feel in the off-season, which is why fall is a great time to explore along the waterfront or find a quiet place to drop anchor and take in the scenery.

 However, boating in the off-season – when the sun sets early, temperatures drop fast and there are fewer boaters to come to your aid or call for help – carries certain risks, and experienced boaters know to plan for every emergency before heading out.

Consider Worst Case Scenarios

 There’s little or no margin for error in the off-season, so consider every possible scenario, beginning with the possibility of being stranded. Be sure you have enough fuel to get where you’re going and back. The rule of thumb is one-third out, one-third back and one-third for emergencies.

 As a responsible boater, you should always carry a first-aid kit, but in the off-season be sure you also have an onboard emergency kit that includes a change of clothes; calorie-dense snack food; fresh water; a thermos of coffee, cocoa or other warm beverage; duct tape; a waterproof portable flashlight with extra batteries; flares and matches. Stow all of these items in a waterproof bag. Remember to stay away from alcohol when you’re out on the water. It impairs your judgment and hastens the onset of hypothermia.

 Carry a mobile phone only as a backup to your VHF-FM marine radio. Mobile phones frequently lose a signal and are unidirectional – only one person receives the phone call compared to many who may hear a VHF radio distress call. If your boating activity takes you far from shore, consider adding an EPIRB as well. Rescue 21, the advanced command, control and communications system created to improve search and rescue, is currently being deployed in stages across the U.S. This new system gives the Coast Guard the ability to pinpoint the location of a distress call from a DSC-VHF marine radio connected to a GPS receiver. If you get in trouble, especially during the chilly off-season, every minute counts.

 Life jackets are essential boating equipment in any season. Lightweight inflatables are popular in the summer months, but in cold weather, float coats and jackets will not only keep you afloat but also provide additional insulation. Since there is rarely time to put on a life jacket during an emergency, make sure everyone wears one at all times while the boat is under way. Also, consider equipping your life jackets with devices to help rescuers find you more quickly (e.g., whistles, strobe lights, signal mirrors and/or personal locator beacons). If you do fall in, stay with your boat, so rescuers can spot you more easily.

 If anyone ends up in the water, think about how you’ll get them back in the boat. Climbing back in after a fall overboard can be next to impossible in heavy, cold, wet winter clothes, even for someone who is uninjured. Consider providing a sling if your boat has no boarding ladder. If you boat in cold weather often, I strongly recommend that you practice (under warmer conditions) getting back in your boat, as well as bringing passengers aboard under cold-weather conditions.

What to Wear

If you go boating in the fall, dress appropriately:

  • Dress in layers and recognize that even slight changes in the weather can make hypothermia a threat.
  • Take extra dry clothing in a waterproof bag.
  • Wear quality, nonslip footwear; wear socks, even with sandals.

Wear your life jacket or float coat/jacket. Cold water quickly saps your strength. Life jackets provide added insulation. If you fall overboard, wearing a life jacket could give you the time you need to safely reboard the boat. The first reaction when hitting cold water is to gasp and suck in water. A life jacket can give you crucial minutes to regulate your breathing after the shock of falling in.

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