What is your preferred method for checking your nav gear for error?

[MarkJ]

I often find a rock and run aground on it for a few days. It checks the depth gauge and if the GPS position moves I just sail away.

[Jim Cate]

Originally Posted by Nikki S

Anyone been to Coffs Harbour, in Australia?
Coming in from the south there, our chart plotter and Navionics both jumped, suddenly putting us a few nm north of where they had been/our actual location. Luckily there are good lead lights so we just used those. In happens on google maps while driving in your car there too..... When we departed, Chart plotter and Navionics were both fine and accurate.
Made me worried about sailing on dark nights in certain areas.

We've been in and out of Coffs many times and have never experienced this error. Were there funny lights in the sky at the time? Might have been a tractor beam seeking to abduct you, and y our GPS was dodging it???

Seriously, that's pretty odd,and kinda hard to explain. But as all good navigators know, the mark I eyeball and a couple of lead lights are hard to beat... and those leaders at Coffs do show up well from offshore.

Jim

[Dockhead]

The killer app for this is radar.

[clownfishsydney]

If you are showing your track on the chartplotter, then it should be obvious if all of a sudden the GPS goes wacky as the track will have a strange jump in it to left or right or forward or back.

[Cadence]

Originally Posted by MarkJ

I often find a rock and run aground on it for a few days. It checks the depth gauge and if the GPS position moves I just sail away.

I always love your humor.

[nematon785]

For those of us checking against our dead reckoning, I'm assuming we are plotting on a paper chart and logbook, or are we using an app or something here?

If you are entering a new harbor at night and discover your chartplotter is reading incorrect, and must abandon it for the moment, how many of us have a set of magnetic headings and reference points on a shortlist for piloting in? do people even do this sort of thing anymore?

for paper charts and magnetic backup, a shortcut to keep it streamlined is doing everything magnetic, rather than converting back and forth to true. some folks do not like that, are there any other shortcuts that keep paper navigation quick, dirty, efficient and correct that I can incorporate?

Lastly, if you have someone aboard who is "handling" navigation, what subtle method do you suggest to check they are not way off?

example: "head 187 degrees on your compass" "Uh that runs us through the lineup of surfers and into the breakers... Are you sure you don't mean 7 degrees or something?"

[Suijin]

Please forgive me and no disrespect intended, but your ideas strike me as those of someone with very little experience with all of this equipment. Some feedback:

Originally Posted by nematon785

cross checking the chartplotter against radar would reveal quickly if there is a significant error in the settings.

Provided you're in a spot that will give you a meaningful radar picture. You're going to need coastline for that. If you're in a harbor/bay/etc. you'll know where you are based on the chart plotter chart and your boat position.

Originally Posted by nematon785

depth should follow charted contours so following a series of depth readings against charted depth seems a good cross check also.

Good luck with that. Depths can vary significantly between charted soundings. They are a general ballpark in most cases, and "average" of the bottom under keel, with more or less variation depending on where you are. There are many areas that have not been surveyed in probably 100 years. 95% of the Chesapeake Bay, one of the busiest waterways in the world, for example has not been surveyed since before WW2. I've run around in in charted 12' depths in the Bay due to infamous "Chesapeake Humps".

Originally Posted by nematon785

multiple gps against one another, ie all coordinate readouts should be very close from phone, handheld, laptop with puck and primary nav station

Indeed.

Originally Posted by nematon785

check actual depth at anchor against charted depth and sounding depth

Good for checking and calibrating your sounder. Useless for anything to do with your chart plotter. See above.

Originally Posted by nematon785

Triangulate headland or navigation aid on actual chart, compare against nav station. (compare what you see with what your screen says)

Just sail by a few markers. If they are where they are supposed to be, you're good. If you're within sight of land you're usually able to check the accuracy of your GPS by intuitive dead reckoning. The bigger issue is offshore, where you have no point of reference. That's when you compare two devices, and you're done.

Originally Posted by nematon785

With NMEA all in one MFD where radar, gps, depth, and chart are all wrapped into one display, I wonder how independent each part of the system is? Can I still run independent tests if everything is basically on one computer and running one type of software, possibly with centralized user settings causing an error to carry across all functions?

Data from each sensor/device is shared on the N2K bus, to be consumed by any device that can use it. It would be extremely unlikely for all the data to be corrupted. If in doubt, you just start unplugging stuff to see where the problem is.

Originally Posted by nematon785

What method do you fine folks use when the rubber meets the road out there to check you nav gear? how often do you double check it?

I live on the boat and use my nav gear virtually every day. If something is wrong, I usually know about it immediately. Modern gear is very robust. Other than the paddlewheel, or wind anemometer (moving parts), most stuff either works properly or it doesn't at all, rarely giving erroneous readings. GPS in particular I have never had give a consistently incorrect position if it has adequate satellite fixes.

[zeehag]

my gps placed me in a parking lot 500 ft away from my actual location, and my spot placed me on other side of a channel from my stationary location. yup all are off about 500 ft off in different directions. i love it.
guess i wont be finding amelia earhart......
i love watching folks entering the lagoon at barra de navidad for first time, using gps for the tricky and narrow channel--they invariably turn sharp left instead of going from the point at the marina to the little beach visible from that point.
excellent entertainment, as all become mud wrestlers.

[Paul L]

Originally Posted by zeehag

my gps placed me in a parking lot 500 ft away from my actual location, and my spot placed me on other side of a channel from my stationary location. yup all are off about 500 ft off in different directions. i love it.
guess i wont be finding amelia earhart......
i love watching folks entering the lagoon at barra de navidad for first time, using gps for the tricky and narrow channel--they invariably turn sharp left instead of going from the point at the marina to the little beach visible from that point.
excellent entertainment, as all become mud wrestlers.

It is a whole lot more likely that the chart is off rather than the GPS.

[Cadence]

I am not sure I understood one rant? GPS is great as was loran C, in its day, but if they fail paper and a compass will get you home, No batteries required. Only some common sense.

[nematon785]

Suijin you are absolutely right,I have very little experience.

Most of myconcern revolves around what I have seen in my limited experience, and what will happen when I become captain of my own vessel, possibly with souls aboard I become responsible for including my own.

It is quite clear to me there is little room for error and high consequences in the world of piloting and seamanship, If I hit something, I may lose my boat, I may drown others may drown, I may hit something expensive and go bankrupt.

On charters,lessons, and other peoples boats I have seen some really crazy irresponsible ****. Including the captain that started drinking before we even arrived at 9am. No GPS onboard other than everybody has a mobile phone. The salty guy in charge initiating a tack while a first timer is sitting on the foredeck sunning herself. deck sweeper anyone? The captain who could not stop, or turn around to save his new hat that went overboard, god help us if it were a person.

No deviation cards at the compass, no charts aboard of any kind, non functioning instruments, handheld gps' floating around the cockpit that only displa lat n lon, (seems useless without a chart to refer that lat lon to until you are barking for CG or tow help on the radio and they ask your position...)

I have tried to operate chart plotters mounted on boats that are so counter intuitive as to be literally useless (no manual available) to me while steering. even the owner was not sure how it connected to the autopilot or how to set it up for general purpose navigation, WTF knows what datum or chart the thing is set on. we just sailed by visual cues (in and out of Marina del Ray.) actually I should say we motored in and out of Marina del ray, and sailed to include one tack to turn around... Easy and obvious visuals with the giant airport.

This is how hiring a yacht with a professional captain and paid ASA 101 and 103 type lessons were handled as well! Everytime we went out everything was done visually. even the night navigation lesson where we spent an hour dicking around with charts at the school, and then went out to the boat. all paperwork was promptly stowed, and we set sail. not even firing up the chartplotter, no interest in AIS, just motor out, motor south east to a navigation bouy, turn around, motor back. we did not even discuss bouys on the way back in. compass headings were ignored the whole time.

this experience will not help me when I make my excursions as captain of my own vessel. Some of this experience was paid training on how to sail and navigate/pilot a vessel. I guess the part where I have seen the harbor entrances and sailed in and out of them will help. not so great if I go to Ventura or Santa Barbaraharbors I have not yet been to, especially if some delay (mechanical or otherwise) results in my arrival at these new ports at night

So I come here to benefit from the vast resources of many experienced sailors. Quite a bit of what I do until vessel aquisition is thought experiment. it is all I can do right now.

Having a well laid out plan is what Piloting is all about right?

[Hydra]

Originally Posted by Paul L

It is a whole lot more likely that the chart is off rather than the GPS.

Sometimes, the GPS is on but wrong. Last summer, I entered a river mouth, passing close to the west of a lighthouse and the GPS showed the correct track. The next day, I came out, passing again to the west of the lighthouse. But this time, the plot was to the east, by a few tens of meters.

Alain

[nematon785]

"Just sail by a few markers. If they are where they are supposed to be, you're good. If you're within sight of land you're usually able to check the accuracy of your GPS by intuitive dead reckoning. The bigger issue is offshore, where you have no point of reference. That's when you compare two devices, and you're done."

I really like this. Thank you.

[Pelagic]

Have not read the other post but to simply the order of checking for errors in electronic nav aids

Think
#1.Test and verify with physical reality like visual transits and lead lines to identify fixed and variable errors

#2. Always confirm the processed information of GPS/PLOTTER with alternate data and measurements using Radar Plots/ depth sounder and paper harbour charts especially if plotter is overzoomed!

Then refer back to #1 and approach new waters with caution.

[Stumble]

Practically speaking, the GPS is correct, everything else is wrong. If you want to confirm the GPS is correct get out another GPS.

the problem is when people treat chart data that was made with a sextant as though it had the same accuracy as your GPS. There are habitable island in the Carribean that are misplaced by 1nm, and a lot that are off by .5nm. Because the chart data isn't as good as the gps data.