Monthly Archives: February 2014

What is AIS?

Rule 9AIS is intended to help ships avoid collisions, as well as assisting port authorities to better control sea traffic. AIS transponders on board vessels include a GPS (Global Positioning System) receiver, which collects position and movement details. It includes also a VHF transmitter, which transmits periodically this information on two VHF channels (frequencies 161.975 MHz and 162.025 MHz – old VHF channels 87 & 88) and make this data available to the public domain. Other vessels or base stations are able to receive this information, process it using special software and display vessels locations on a chart plotter or on a computer.

If you like tracking ships or just like being nosey, you can use the Marine Traffic website to do just that. You can move around the map and zoom in on your area and see what commercial traffic is there, what direction it is moving and at what speed is it moving. If you live in an area where you often see commercial ships that you wonder about just look them up real time as they pass by. Use the following link to visit the Marine Traffice site.  http://www.marinetraffic.com/ais/default.aspx?level0=100

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“Magenta Line” To Get a Safer Route

Courtesy BoatUS:

It’s over 70 years old, a thin magenta-colored line appearing on over 50 different navigational charts covering the Atlantic Coast and Gulf, snaking along the route of the Intracoastal Waterway. Now, thanks to NOAA’s Office of Coast Survey and a public-private partnership with Active Captain, an interactive cruising guidebook, NOAA will be updating the “magenta line” on all of its newly-issued navigational charts to help keep boaters in safe waters. Boat Owners Association of The United States (BoatUS) submitted comments on the proposal to NOAA, who had initially proposed removing the line entirely. However, responding to BoatUS’ and other boaters’ comments, NOAA will tap into users of Active Captain to update the route in an on-going effort that will benefit the boating community.

“Some boaters had assumed the magenta line, which was last updated in 1935, was a precise route through safe waters,” said BoatUS Government Affairs Senior Program Coordinator David Kennedy. “However, over time the forces of nature made the line inaccurate as shoals shifted and underwater topography changed, leading some boats into shallows, over dangerous obstructions, or even into land. We thank NOAA for a change of course in keeping the magenta line, listening to boaters and coming up with a creative public-private partnership that recognizes the value of this important guide to navigation.”

For more information on Nautical Charts and Navigation Techniques visit http://boatsafe.com/navigation.

The magenta line appears in charts covering all Intracoastal waters, and is essentially two distinct routes along the eastern US and Gulf Coasts totaling about 3,000 miles in length. Said Captain Shep Smith, chief of NOAA’s Coast Survey’s Marine Chart Division, “Today’s decision to reinstate the magenta line is not a quick fix. It will take at least three years to fix problems that were 70 years in the making.”

Boaters may contribute to the updating effort by joining Active Captain at https://activecaptain.com/

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Introduction to Navigation Part 7 Estimating Time of Arrival

This will be the end of our  7 part series on “Introduction to Navigation.” We hope that we have given a brief overview of what you would be learning in the Nautical Know How Coastal Navigation Course. Trust me there is much, much more that we did not touch on.

Learning the “Art of Navigation” is not difficult but there are several steps that must be learned along the way. After learning about latitude and longitude, distance, direction and reading a nautical chart, you will start putting these processes together to solve real-time problems. On piece of practical information you might want to use is estimating time of arrival.

These basics are covered in the online Nautical Know How Basic Boating Safety Course at http://boatsafe.com/navigation .

Assume that you will leave your marina or boat ramp on a trip to a nearby restaurant for lunch.

  • You have made reservations at the restaurant for 1200.
  • The restaurant is 29 nautical miles from your marina.
  • You plan on a leisurely cruise at a speed of 12 kts.

What time must you leave your marina to arrive at the restaurant at your reservation time?

This is a simple Distance, Time, Speed question. The formulas to use for the calculations are made simple if you remember, and actually write in a corner of your chart, the following diagram.

The “D” represents distance, “S” represents speed and “T” represents time. In order to solve a distance, speed, time problem you need two of the three values and then must solve for the third.

Using the diagram, cover the unknown value with your finger and what you have left is the formula to solve the problem.

In our problem we know the distance and the speed so we cover up the “T” and the resulting formula is “D” over “S” or “D” divided by “S”.

Using this formula, the first step is to calculate how long it will take you to get to the restaurant by cruising at 12 knots for 29 nautical miles.

29 / 12 = 2.42 hours

Note: This is not two hours and 42 minutes, it is 2 hours and 42 hundredths of an hour. We now have to convert this decimal to minutes by multiplying .42 X 60.

.42 X 60 = 25 minutes – So…our trip will take 2 hours and 25 minutes.

Now that we know how long the trip will take, we simply need to subtract that time from the time of our 1200 reservation.

1200 – 225 = 0935

1160 – 225 = 0935

Note: that in order to subtract we had to borrow an hour from the hours column. 1160 is the same as 1200. We must leave the marina or boat ramp at 0935 (9:35 am) in order to arrive at the restaurant by noon.

If you would like to learn more about Time, Distance, Speed calculations or other aspects of navigation, check out our Nautical Know How Coastal Navigation Course.

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/

https://boatsafe.wordpress.com/2011/05/19/introduction-to-navigation-part-6-time-calculations/

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