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post #3 of Old 02-02-2011
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Originally Posted by harbin2 View Post
A year ago, I could see little value in having a chart plotter other than as a toy. I got one anyway and now my view has changed fairly drastically. In the last year, I have spent a lot of time trying to understand a lot of the features but I still feel like I have a ways to go in understanding what to use it for. As an analogy, you think of your car as something that gets you to work, gets you to the store, takes you on vacation, etc. You don’t really think much about how the engine or transmission work. What you use a chart plotter for is not quite so obvious – not to me anyway.

Unfortunately, none of the GPS instructions I have seen tell you what to do with the devices. They just tell you how they work. So I now know how to create a waypoint but knowing why I would want to create one isn’t so obvious. Below is a list of what I can think of that I have used my chart plotter and software for.

If anyone routinely uses their software or plotter for anything I don’t list, please add your uses so we can all get maximum benefit out of these amazing devices.

1. Trip planning – casually, almost day dreaming, about cruises.
2. Trip planning – creating actual routes that will be used to cruising destinations.
3. Record good anchorages that normal charts would have you believe are inaccessible.
4. Locate and get info on marinas.
5. Great for tide info. – for planning
I would point out that trip planning using a chart plotting software package is not the best idea.... using waypoints that you have not physically been to and relying on them is at best risky. You have no idea of how accurate your electronic charts are in a specific region or area, and basing actual routes on them without doing the basic research using the pilot books and paper charts is unwise.

BTW, if you think using software to get in and out of anchorages that have risks or obstructions according to the paper charts is a good idea, you might want to take up another hobby.

The information on marinas is nice, but remember it is a static snapshot in time, and marinas change hands, go out of business, and such fairly often, especially in times of economic hardship. The information found in cruising guides and charts--both electronic and paper--is often out of date by the time it is published.

Chart plotter
1. Determining current position when position is uncertain or unknown
2. Cutting corners – following shoal lines vs. navigating buoy to buoy to save time and distance.
3. Provide detailed depth information to assist in anchoring up small creeks.
4. Provide trip data such as speed.
5. Determine actual tide current by comparing gps speed to knotmeter speed.
6. Backtrack out of a morning fog by following yesterday’s track.
7. Determine distances to objects over a mile away.
8. Tide Info.
Using a GPS as your only method of determining your position when uncertain is less that ideal. If you are in sight of land, using coastal pilotage skills and techniques makes far more sense, since these will locate you relative to the land, and not relative to some cartographer's electronic rendition of the actual area.

There's a reason you navigate from BUOY to BUOY... cutting corners without local knowledge is stupid and risky.

Getting depth information from an electronic chart is also stupid. The depth information isn't going to account for shifting sandbanks and shoals, and was of questionable accuracy when the data was collected, much less months or years later, when you're actually using it. Your depthsounder is a much better choice for depth data, especially since the numbers on the chartplotter don't account for tidal variation in depths.

Using a GPS to backtrack is fine, provided the accuracy of the unit at the time you do so was high enough when you made the track in and are following it out. That isn't always the case, and the more critical the navigation, the less I'd rely on the GPS. Use your Mark I EYEBALL instead. Even in fog, you can get a fair bit of information from it. For instance, if you're entering a narrow channel, say 80' wide, and your GPS had an accuracy of +/- 20' when you made it and has an accuracy of +/- 20' when you follow it out, you could be 40' from the center of the channel. That could be really bad, especially in something like the ICW, where the channel's edges are often laden with things like submerged tree stumps.

If you need to determine distance to objects over a mile away, use radar. It is very accurate for distance bearings, not so good for compass bearings.


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Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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Last edited by sailingdog; 02-02-2011 at 07:48 AM.
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