NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: DR navigation in the recreatiional fleet: was Role of CN at s ea
From: Derrick Young
Date: 2004 Oct 13, 11:35 -0400
From: Derrick Young
Date: 2004 Oct 13, 11:35 -0400
You have very clearly stated the issue that most educators are faced with - the tools (such as GPS) are readily available and can be purchased/used by anyone. For most folks, knowing current position as well as having some historical data would appear to be sufficient. Most boaters never leave sight of land and are familiar with their immediate area. They want confirmation of where they are, how far they have traveled, how fast, fuel consumption (though some don't understand why), and how to get back to their dock. They ask "Why do they need to understand the basics of piloting (LOPs, DR plots, current/leeway, etc.)? I can only tell you what I do to answer this question - this may/may not work for you. I make sure that they are aware that a sextant, RDF, LORAN, RADAR, SONAR/depth finder and GPS are nothing more than tools of the trade for a competent navigator. They allow you to determine and/or confirm your position by reference to external objects such as charted elements (piloting), stars/planets (CN), radio beacons (RDF/LORAN - electronic nav) and orbiting space junk (GPS - again electronic nav). Most folks forget (or get too wrapped up in the buttons and displays to remember) that GPS (and e-nav in general) provides current position (a fix) and the heading between the last updates - everything else it either remembers or computes. It does not understand of what is between you and the target (destination). If you stray off your pre-determined course (your DR plot) (effects of current/leeway), GPS will provide you a new heading to your intended target. This begs the question, what lies between you and the target (reefs, sand/mud bars, dry land, swamp, etc.)? GPS and other generally available e-nav products do not supply or act upon that information. A number of my students have asked about/stated and/or argued, "my GPS has all of the charts of the area, so can I rely on that heading." I have yet to find a publicly available GPS that will automatically determine and add waypoints around charted objects. Unless the student has done this, the heading that they see is from their current position to the target regardless of what is in the way. This is not an issue when you are at sea, but it is an issue when you are closer to land, in a bay or river. In a GPS familiarization course, I start by talking about our local area and it's conditions. We boat on a lower James River (Virginia), the port of Hampton Roads, the Chesapeake Bay and mid-Atlantic coast. We have lots of commercial traffic, shoals, mud flats. Where we are, the river is 1.5 miles wide, but most is only 6 inches deep at low tide (there is a 300 wide channel - but not necessarily in the middle of the river). I put a local chart (12251) on the wall and have them pick starting and destination points. Using a string and a couple of push pins, I show them what heading their GPS will show if that is all of the information that they have. Invariably, this has them boating across mud flats, dams, dry land and all of the other water hazards. From here, I go into understanding basic chart information (DATUM, chart projections, survey dates, scales, lat/long and updating), then how to locate a position on a chart. Amazing how many cannot find their lat/long on a chart. Then back to the GPS - they need to understand the quality of a fix, waypoints, routes and tracks. During the first couple of hours, I have been able to develop a basic understanding of piloting and chart work. They are now ready to start learning how to use their GPS in conjunction with a chart. Here I return to the question of what track do we follow from our launch point to where we want to destination (target). This leads right into what heading to we use when we are off course and need to return to the track. I have found that most rec boaters do not use charts because they do not understand them. They purchase a GPS because of all of the bells and whistles that are there. For many, the GPS chart display is as close as they have been to a nautical chart. This display gives them a false security because they have no idea as to when it was generated or last updated. When we have gotten this far, I spend time working through some of the different GPS units, showing the menus, options and buttons. Hopefully, they have brought their GPS so that they can understand things on the unit that they are using. I cover as much as the students can handle and tailor each session for the folks that are there. After all, a bass boater has different needs from the weekend cruiser. Don't know if I have answered your questions or not. If I haven't, let me know. derrick