Uses for Chart plotters and chart plotting software
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
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.
Chart Plotter #1,#2, #3, #6 & #7.
As long as one remembers that your chart plotter tells you where you theoretically are located. Which is affected by GPS satellite issues and errors on the charts loaded (and there are chart errors).
I still make use of my eyes and refer to paper charts in addition to my chart plotter.
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.
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.
Here's about the only things I completely rely on with the chartplotter. I use the speed over ground display to determine when I've actually come to a halt to drop the anchor. Not that critical, but nice. I also leave the anchor alarm on for 15 or 20 mins to see if we set. That has alerted me to dragging when I'm distracted by other things. Still, I would have figured it out on my own in time, just nice to have. I also confess that I take its word for time to waypoint and/or VMG, but only for cruise approximations, not specific dead reckoning navigation.
Now, as far as simultaneous navigation to a chart, its fantastic. It just needs to be cross referenced.
On my chart plotter the entry into Spanish Waters in Curacao put me in the Hyatt Hotel swimming pool and the Boca Grande entry into Cartagena placed me on the reef.
Where I am now moored, Puerto Morelos Mexico it is out by 800 yds.
I use my chart plotter as a general reference and guide to supplement paper charts and guide books.
However, the one thing I do not use it for is accurate navigation...The more I use it the less I do night entries.
Sailingdog has it right...If you can't eyeball it you should not be doing it. Unless your charts are good and up to date and your charting/piloting skills are exceptional.
And Oh yes, never, never cut corners on buoyed entries and channels.
I should have inserted all the obvious caveats about using common sense, paper charts, your eyes, etc. for those who might be new to sailing and think I’m suggesting navigating by chart plotter alone. SD – and others, thanks. I also should not have used the term “cutting corners” since that just evoked negative responses.
However, I would appreciate some responses contributing to my OP. Thanks Minnewaska for your two. As an example does anyone save tracks and view them at home? I’m just not sure I see the value in some of the features. Thanks again for your input.
I'm not saying that you can't use one for route planning...and I use MacENC for route planning regularly... but that you shouldn't be using the waypoints you pick in the route planning as waypoints, until you've actually sailed to where the waypoint it and have checked it to see that it makes sense to use it as such.
Another good use is to see what alternative landfalls you would have in the case of an emergency. I highly recommend writing up a summary of each harbor or inlet that you might have to make an emergency passage into. Include a brief description of the entrance, ATONs to follow, course distances and bearings, etc., so that in the emergency, you're not having to look all this stuff up. It helps prevent mistakes from being made when you're in the emergency and more likely to screw up.
However, almost anything you could do with the chartplotting/navigation software, you could do faster and easier with paper charts IMHO.
A chart plotter can be used quite creatively in many ways. Setting up proximity waypoints can allow you to clearly define an anchor watch and let you know if you're dragging. This is sometimes preferable to using the built in anchor watch feature, since you can customize it specifically for the anchorage in question.
You can also set up proximity waypoints to warn you of isolated, unmarked dangers that might be on your course.
The cross track screen can help you realize if you're being blown or pushed off course.
Using the GPS and checking your COG versus your heading, you can see what the effects of set and drift are on your course in many cases. Heading is the direction the boat is facing, COG is the actual direction the boat is moving in, and rarely are they the same.
I've seen firsthand the inaccuracies in charting software - esp in Mexico around Tenacatita and Manzinillo though it's likely a problem everywhere there.
On the flip side I've been astounded at times by the accuracy here in the PNW. Our son bought a boat in Tacoma and we took it home to Vancouver on a cool March weekend, planning a two day trip.
As evening approached it was clear and we had a good moon so we decided to carry on. I had pre-planned our trip and had the route loaded into our Garmin MAP76. We did have radar. The trip plan was through the LaConner canal appropriately known as 'the ditch' and I'd put about 20 waypoints through that stretch (about 10-11 NM).
We had some moonlight, and lots of light in La Conner so with radar we were fine, but in fact we sat on the "Highway" that is the route line on the GPS the whole way after dark. Arriving in Anacortes at midnight we were able to find some fuel and carried on arriving home after 31 hours straight.
Still, attempting such a run without any visibility or radar would be foolhardy.
How does anyone get anywhere new, if they don't aim for it? Easiest way to aim for it, is to assign it a waypoint and steer towards it. I totally agree that you can't assume that your new waypoint will be a safe waypoint, but that should become apparent as you approach it.
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