General Navigation Techniques
<HTML><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8></TD><TD vAlign=top align=left width=350><IMG height=300 src="http://www.sailnet.com/images/content/authors/sexton/102701_js_navigation.jpg" width=350><BR><DIV class=captionheader align=left><FONT color=#000000><B>Successful coastal cruisers are well acquainted with the basic elements of navigation. </B></FONT></DIV></TD></TR><TR><TD colSpan=2 height=8></TD></TR></TBODY></TABLE>In an earlier article I classified the primary phases of navigation as Inland Waterway, Harbor, Harbor Approach, Coastal, and Ocean (see <A class=articlelink href="http://www.sailnet.com/forums/showthread.php?threadid=19015"=>Navigation Phases=</A=>=). The Harbor and Harbor Approach navigation phases can also be called departure and arrival, and the Coastal and Ocean phases can be broadly combined as navigation underway. For each phase I explained the different aids to navigation used. Now I would like to discuss in detail the navigation techniques used within these phases. <P>First off, no matter where you are going, you will need to do some planning. In the planning stage you will draw the course lines on your chart from the departure point to the arrival point. These two points may not necessarily be your berth positions. The departure and arrival points, in most cases, will be the buoys that mark the entrance to the harbor, channel, inland waterway, or traffic lane for that port. For coastal routes you will usually have several waypoints along the way as you proceed from buoy to buoy, avoid hazards, and go around islands, points of land, rocks, or reefs. <P><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8></TD><TD vAlign=top align=left width=150><IMG height=272 src="http://www.sailnet.com/images/content/authors/sexton/050500js_jrmap.gif" width=150><BR><DIV align=left><FONT color=#000000><B>The first part of the preparation stage is pre-departure knowledge of distances and courses you'll be sailing.</B></FONT></DIV></TD></TR><TR><TD colSpan=2 height=8></TD></TR></TBODY></TABLE> After you have all the lines drawn, measure the true course and distance, and label this information along each line. Place the course above the line and the distance below it. I also like to record this information on a navigation log along with my predicted speed and estimated time en route (ETE) for each leg. By summing up the ETEs, I can determine the total en route time. Once I know my actual departure time, the estimated time of arrival (ETA) can be easily calculated. For each waypoint I will also measure and record the latitude and longitude for use in the GPS. <P>On the chart, I like to highlight important information with different colors, making it easy to use while underway. For example I use yellow, red, and green for the important lighted buoys; I also use yellow to highlight navigation channels and ranges, depth contours, and the variation in the compass roses. I also like to draw additional latitude and longitude lines to make the plotting easier and highlight the latitude and longitude degrees and minutes on the edges of the chart. I can gussy up my navigation chart all I want as I use a new chart every time I go out. The old charts along with the deck log are filed away after the voyage is complete. <P>Now, if you are using one of the computerized navigation and electronic charting programs, this planning stage is easily done. Once finished it can be printed out and the waypoints uploaded into the GPS with a few clicks of the mouse. I would also highly recommend that you plot these points on a regular paper chart for use while underway. If you use the ChartKit charts, most of the coastal routes have been plotted and annotated with the course and distance between prominent buoys and waypoints. <P><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8></TD><TD vAlign=top align=left width=164><IMG height=258 src="http://www.sailnet.com/images/content/authors/sexton/050500js_dayboard.jpg" width=164><BR><DIV align=left><FONT color=#000000><B>Keeping track of navigation aids makes life aboard less stressful in harbor and channel situations.</B></FONT></DIV></TD></TR><TR><TD colSpan=2 height=8></TD></TR></TBODY></TABLE>For the departure phase, I place an entry in the logbook that reads "departure from" and record the cast-off at local time and the precomputed distance and travel time to the departure point. The process of getting out of a harbor varies considerably from place to place and can be as simple as casting off and heading directly for the harbor entrance buoy, or as complex as following several different channels, range markers, and traffic lanes to a mid channel buoy. Getting out of most harbors also includes avoiding lobster or crab traps, moored vessels, and other maneuvering boats. For this reason, the departure phase is usually done under visual conditions using the radar and the depth finder and doesn't involve any formal navigation procedures, chart plotting, or logging—unless you are in a long channel or a traffic lane. In this case, record the turning points and times on the chart along with your average course and speed until you get to your planned departure point. During the harbor departure, refer to your chart and follow the buoys, channels, and range markers. The rules of the road will often come into play as you encounter other vessels while departing a busy harbor. At the departure point annotate the chart with a fix symbol (a full circle) and the local time placed horizontally near the fix symbol. Also record the departure time, course, and speed in the navigation log book and the deck log. Give the desired compass course and deck log to the helmsman. Make sure that there are no misunderstandings between the two of you concerning exactly what you want for a course. For more information on the desired course versus the actual course, see the SailNet column titled <A class=articlelink href="http://www.sailnet.com/forums/showthread.php?threadid=19056">Dead but not Deceased</A> by John Rousmaniere. <P><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8></TD><TD vAlign=top align=left width=221><IMG height=271 src="http://www.sailnet.com/images/content/authors/sexton/050500js_devlinboat.jpg" width=221><BR><DIV align=left><FONT color=#000000><B>Professional work in the chart room can save the need for professional work in the boatyard later on.</B></FONT></DIV></TD></TR><TR><TD colSpan=2 height=8></TD></TR></TBODY></TABLE>On a crewed boat, the helmsman will make every effort to hold the desired course and speed, but there will be times when that may not be practical or possible. For this reason the helmsman will record the actual compass course and speed steered and the time of any change of either one. Minor maneuvering to avoid lobster traps and other vessels need not be recorded. When it comes time to plot a Dead Reckoning position, the navigator will use the deck log recorded information. Never assume that the helmsman held the desired heading and speed. To do so can lead to a dangerous situation or at best to a lost or confused navigator. In my 30 years as a professional navigator, I was never lost. Temporarily misplaced or partially confused, yes, but never lost. In one of his columns, John Rousmaniere writess about an important long-distance race that was lost because the helmsman compensated for leeway when steering a course without telling the navigator who had already done so in setting the course. The result was that they ended up several miles to windward of the mark—one more illustration of the importance of clear communications. <P>Obviously on a small boat with minimum crew, the navigator and the captain of the vessel can be the same person, while a family member or close friend acts as the crew and helmsman. In this type of situation the voyages are usually short, with the exception of the long-range cruising families. Whatever the crew situation, it is always best to take a professional approach when it comes to navigation and seamanship. <P>For navigation while underway, the three basic principles of Dead Reckoning must be followed: </P><P><TABLE border=0><TBODY><TR><TD width=10></TD><TD vAlign=baseline width=29><IMG hspace=12 src="http://www.sailnet.com/images/content/authors/Bullets/seamanship_bullet.gif"></TD><TD>A DR can only be started from a known position</TD></TR><TR><TD width=10></TD><TD vAlign=baseline width=29><IMG hspace=12 src="http://www.sailnet.com/images/content/authors/Bullets/seamanship_bullet.gif"></TD><TD>Only true courses actually steered are used for the DR track</TD></TR><TR><TD width=10></TD><TD vAlign=baseline width=29><IMG hspace=12 src="http://www.sailnet.com/images/content/authors/Bullets/seamanship_bullet.gif"></TD><TD>Only the speed through the water is used for calculating the distance traveled. </TD></TR></TBODY></TABLE></P><P>A DR position must be plotted every hour on the hour, at every change of heading or speed and at every fix. Until a fix is obtained, you must continue plotting the DR position from the preceding DR position. You may plot an Estimated Position (EP) using predicted set and drift or perhaps a single Line Of Position from a depth contour or bearing off a buoy, but the DR will continue from the DR position and not the EP. <P><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8></TD><TD vAlign=top align=left width=222><IMG height=162 src="http://www.sailnet.com/images/content/authors/sexton/050500js_marker.jpg" width=222><BR><DIV align=left><B><FONT color=#000000>Arriving in an unfamiliar harbor always requires prudence and often patience.</FONT></B></DIV></TD></TR><TR><TD colSpan=2 height=8></TD></TR></TBODY></TABLE>When you arrive at the entrance buoy for your destination, record the time and annotate the fix on the chart. The arrival phase into the harbor and to the dock or mooring point will use the same navigation procedures and techniques as the departure phase. <P>In addition to Dead Reckoning, by plotting on the chart by means of course and distance from a known location, you can also do DR by computation. The various methods of DR computation by calculation are collectively called the Sailings. Of the eight different types of Sailings listed by Bowditch, the ones most commonly used are Great Circle and Mercator. For voyages of less than 200 miles, either one will give accurate results, but the Mercator calculations are much simpler. But, for long distances you will need the accuracy of the Great Circle calculations. For those of you who are interested, the Sailings are discussed at length in Bowditch. I would suggest that you take the Advanced Piloting course offered by the US Power Squadron if you want to know more about these methods of DR calculations. Several computer software programs also make these types of DR calculations for you as part of their log-keeping options and for serious navigators they are well worth considering. <P><EM><FONT size=2><STRONG>Illustrations by Mark Smith from The Annapolis Book of Seamanship, by John Rousmaniere, Third edition (Simon & Schuster, 1999)</STRONG></FONT></P></EM></HTML>
|All times are GMT -4. The time now is 11:17 AM.|
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2015, vBulletin Solutions, Inc.
User Alert System provided by Advanced User Tagging v3.1.0 (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
(c) Marine.com LLC 2000-2012