Are navionics the best charts?

dylanwinter

dylanwinter

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www.keepturningleft.co.uk
On the trip from the Fal to Crinan we had two ipads on board - neither mine by the way

I was really impressed with them

Baz had the Admiralty charts and Ian had the Navionics

The navionics gave some brilliant subsea contours for when we were playing in the shallows

the admiralty graphics seemed a lot cleaner some-how

is there anything better than navionics - I fear their arrival on a tablet near me is not far away

D
 
Dylan, really.......

You know full well:

The battery will run out
The screen will break
The gps will fail
You will run aground and die

You need the forum approved system:

Paper charts.
Dividers.
A log.
A pencil.
A clock.

I really can't see this new fangled stuff catching on........
 
Be very, very careful with Navionics "brilliant contours": they come either from user-contributed data (and they have no idea about tides, I have lot of examples if you wish), or very often they are "computed" contours: starting from the basic HO data, they rebuilt a mathematical surface of the bottom, then "slice" it with horizontal planes ad libitum to increase the number of contours, which of course appear nice but have no navigational meaning.
If you are used to have data from an HO and used to its limitations, mixing/adding other type of data which is not built to the same standard is plain wrong, if not dangerous.
Ok criticism on conceptual grounds :D
 
Roberto said:
Be very, very careful with Navionics "brilliant contours": they come either from user-contributed data (and they have no idea about tides, I have lot of examples if you wish), or very often they are "computed" contours: starting from the basic HO data, they rebuilt a mathematical surface of the bottom, then "slice" it with horizontal planes ad libitum to increase the number of contours, which of course appear nice but have no navigational meaning.
If you are used to have data from an HO and used to its limitations, mixing/adding other type of data which is not built to the same standard is plain wrong, if not dangerous.
Ok criticism on conceptual grounds :D
Click to expand...

blimey - and I thoughtit was telling us where the bottom was - that does not sound good - I was getting a bit gungho with those lovely scottish wobbly bottoms
 
It's all so cheap now you can have both. I draw routes on the Navionics in bed over my morning tea. I bluetooth them to my laptop where I have the UKHO charts and use SeaClear. I upload them to a Garmin handheld in the cockpit.

What you DO WANT on the West coast is the Antares charts. I use them in SeaClear.

Oh and all that stuff about depending on electronics being risky is bowlocks. For ten years I always carried a spare computer and never once needed it. Nowadays, with a couple of crew, we usually have:
1 Computer (sometimes two)
2-3 Tablets
3 Phones
2-3 handheld GPSs
All capable of decent navigation and with no common point of failure.

At least two of the devices are set up to be capable of running on AA batteries - of which I carry about a hundred.

And yes, I do have paper charts, a hand bearing compass dividers and a Portland plotter.

This on a piddling little wooden boat.

Aside: The Navionics for Android gets on my tits because it doesn't allow import of data from other systems. I have hacked the export problem. If you hack the import problem let me know.
 
Personally I like Imray Raster and that's what I'd use if I was looking at a single solution (ie a standalone tablet). On the boat we have Navionics on both the chart plotter and a PC, as well as Imray raster and Imray paper!

The important thing to remember is that EVERY map (and chart) is a model of the ground, not an absolute representation of it; and every model is an approximation.

For this reason I don't bother with the 'brilliant subsea contours' (Navionics Sonar Charts) because they are still just a model approximation- albeit with a higher data density than the 'standard' charts, but for my purpose of sail cruising, no more fit for purpose.

Before making decisions on chart packages ask yourself what sort of model the chart represents and what sort of questions you need it to answer for you. This will guide a solution- and you have done very well with paper so far.

I should add that the above is about the charts themselves only- electronic charting software, used to display them, brings a whole other set of advantages which are not directly linked to the question of what sort of model the charts represent. Because some charts are only available with some software, software tool decisions will also influence your choices.
 
roblpm said:
I really can't see this new fangled stuff catching on........
Click to expand...

Ha ha. Maybe you should chuck the engine overboard too ;)

Love my Navionics on a Nexus 7.
I'm careful with the power and have a long cable, spares and a portable battery back up.

It could get wet or go flying across the cabin at the worst of possible moments.
If I was going on a major trip Id definitely have a back up screen on board.

And even in benign conditions you can find yourself looking at a screen rather than looking outward into the environment.
Same with cycling gadgets. sometimes its better just to switch em off.

I do have charts (and enjoy them) and would agree they are essential gear.

But I really do love knowing which side of a sand bank I am, or to be able to check drift or speed over ground.
Definitely safer for that and more relaxed as a result.

Are there better maps out there?
I have not got much experience of other E Map systems so I can't compare.
But the marked creek channel to Faversham was perfect to within a foot or two. Amazing.

I'm happy with this set up for a season or two but may end up getting a laptop plotter.
OpenCPN looks interesting.
I have no idea if its better but if i graduate to channel trips AIS would be nice to have.

Dylan, I can't believe you have not got one to be honest.
 
Depends on what you want to get out of your charts. The vector charts such as your Navionics are good for the flexibility of zooming in and out to see greater levels of detail, plus the add ons such as the contours you have been using. However, raster charts such as Imray or the Admiralty ones you can get with Memory Map are easier for getting the big picture because all the detail is there on one sheet. I have Garmin Bluechart on the plotter and Memory Map and Absolute Tides on a Hudl. The Hudl is more a substitute for the paper charts and tidal atlas (which I also have).
 
Suggest you read this to get an idea how electronic charts are developed. More Googling may help. https://en.wikipedia.org/wiki/Electronic_chart_display_and_information_system_(maritime)
Go with the experience of users in your sailing area. Not all electronic charts are equal for a particular area.
They are all produced from spot soundings taken off existing paper charts(or their digitized data) for a particular area.
Therefore,a particular digital chart cannot be more accurate than the spot soundings(paper chart) that it was made from.
The only folks who do actual spot sounding is the hydrographic service AFAIK. All other E charts are copies.
Charts are made by joining spot soundings with straight lines.
Sometimes,the E chart can be less detailed,depending on how "densely" the mfgr copied the spot soundings.
Go with local knowledge & experience when deciding on charts other than those produced by the Hydr. Service.
Always carry the official paper version,& check your E chart against the official paper chart often.
 
dylanwinter said:
blimey - and I thoughtit was telling us where the bottom was - that does not sound good - I was getting a bit gungho with those lovely scottish wobbly bottoms
Click to expand...

They've definitely made some dramatic cockups in the past few years - I remember threads about a phantom deep-water channel across the drying oyster-beds at St Vaast, and non-existent drying banks in the Solent.

Pete
 
I found Navionics to be an abominable company to deal with and would not give them another penny of my money.

Check out the Visit My Harbour unified charts Dylan. You can have a copy on a laptop with Seaclear or OpenCpn and two copies on tablets with an app. Entire UK and Ireland is about 30 quid.
 
I use Navionics on an iPhone and an IPad. It's good BUT only as good as the chart it is derived from. So you know where you are within a few metres of a point on the chart that was last surveyed in the late 1800's to an accuracy of half a mile (well in the Med anyway). However if you are aware of the limitations a good tool.
 
Navionics on iPad and iPhone is, imo, about as good as it gets. The gps positions are fine, generally speaking the charts are accurate and you can fiddle easily with the level of detail shown, especially the contour lines (which, as others have said, are largely extrapolations rather than actual depths). I've used the apps in the Med and UK and they're my weapon of choice for route planning and occasional close navigation in the final stages of approaches to unfamiliar locations as the monochrome chart plotter at the helm has a clunky zoom which often obliterates details when the selected level of zoom isn't in the original chart.
That said, bear in mind that all chart plotters are only as good as the original data much of which was obtained using lead lines and sextants in the nineteenth century........ And some bits of charts are still using a datum other than WGS84: a classic example is the approach to Messilonghi, where at certain levels of zoom the plotter reckons you're sailing along the road, whereas changing the zoom level brings you back into the middle of the channel.
 
I like Admiralty charts and keep little else onboard for continuity. It would be nice to have them on the Hudl but I can't be bothered.

Two plotters one with ancient Navionics the other with colour C Map keep me informed on the boat. I generally just look at the little pitcher but with cynicism. Both have their shortcomings with vague, disappearing features. No wonder that racer ran into an island in the Indian Ocean. I ask myself how much use can the rehashed data be on multiple devices.

I guess you need to have a PC on board, I don't, heaven be praised.
 
Navionics charts are fine and the software app has good use ability IMO. All vector type charts have the same drawback however in that some details will be missing at higher zoom levels so you should make sure that you check the whole route at low zoom for hazards. I don't think that raster charts have the same drawback.
Even paper charts are not 100%, some areas of the UK and Europe haven't been surveyed since the Napoleonic wars and more remote parts of the world were charged by Captain James Cook. Keep your eye on the depth sounder.
 
Barring the Antares Charts and some harbour areas, there is only one source of chart data in the UK, and that is the Hydrographic Office, who provide the Admiralty charts. All other chart suppliers take UKHO data and repackage it for various markets; it is the same elsewhere in the world, where the data are from the relevant Hydrographic Office (often the UKHO). Of course, the extra step of reformatting and repackaging the data can introduce errors, and we have seen examples on these forums where this has happened, introducing spurious drying areas and omitting islands.

Concerning depth data, the ONLY reliable depth data on a chart are the soundings. All contours are interpretations of the soundings, though on HO charts, they are often based on more soundings than can be shown on the chart; in that case, the soundings will have been chosen to be representative of the depths in their vicinity. Further, the Navionics Sonar Charts, being based on user supplied data, are precisely as good as that data - which can vary between excellent for people who take the data collection seriously and obtain all the proper corrections to downright misleading where people have not allowed for tidal and meteorological corrections. The latter can only be corrected for against a nearby tide gauge, and can make a metre or more difference in the worst case. However, you, the end-user, have no way of knowing whether the data are good, bad or downright dangerous! It is one of those ideas that sounds great on the face of it, but is actually only useful in areas where there is a high density of data input, so that errors in the submitted data become apparent. Errors become more likely in areas with low densities of contributors.
 
duncan99210 said:
a classic example is the approach to Messilonghi, where at certain levels of zoom the plotter reckons you're sailing along the road, whereas changing the zoom level brings you back into the middle of the channel.
Click to expand...

Even better with C Map going into Lakka where your track takes you over the hill to the east of the entrance and across the school playground before you end up on the quay. At least it is consistent as you follow the reverse going out!
 
AntarcticPilot said:
Errors become more likely in areas with low densities of contributors.
Click to expand...

Exactly - presumably the Martian canal at St Vaast was the result of one boat sneaking over the oyster-beds at high water, with no correction made for the tide.

I could never see it being sensible to leave such corrections to the end users, so I assumed they took raw depths along with timestamps and applied a tidal hindcast back at Navionics HQ (obviously can't help with the air pressure). I wonder whether this assumption was wrong, whether the correction process somehow screwed up, or if the data was just completely bad due to a miscalibrated transducer offset or something?

I don't think my plotter can display the user-supplied layers anyway, but if it did I would certainly leave them turned off most of the time. Might take a quick peek (with associated handful of salt) where survey data is lacking.

Mostly I still like to use a paper chart on the table for overview and where the plotter picture is unclear.

Pete
 
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