Navionics symbols (esp depth and drying heights) on iPad

[Keith-i]

I'm preparing for some navigation along the Brittany coastline and have been consulting various charts, including Navionics mobile on my iPad. Whilst most of the symbols and details are standard stuff I keep coming across numbers in brackets starting with a minus symbol and finishing with the letters MT after them e.g. (-18MT) What the hell do they mean? Depths seem to be shown in the normal fashion as do drying heights, but these just don't make sense to me and there doesn't appear to be any correlation with paper charts. The Navionics website is particularly useless with its FAQ's and the only online reference I can find is that they use NOAA symbols.

 

[JSYmartini]

I've just cross-referenced a few with Bluechart Mobile, (-1.8MT) does appear to mean "dries at 1.8m" but I've also found quite a number which for instance may read (-5MT) but Bluechart says its 5m above MHWS.

Hence the disclaimers

 

[Tomahawk]

There are a lot and I mean lot of isolated needle shaped rocks that stick out arounnd Brittany... -5 is quite likely..

 

[Keith-i]

I've just cross-referenced a few with Bluechart Mobile,

Don't get me started on Garmin and Homeport! When I zoom in on my chart I gain detail to start with and then it reduces again as I step in a bit closer. One minute you have the names of beacons showing and the next they're gone. Not to mention the erratic font sizes they seem to use.

 

[scotts_mist]

From the Navionic FAQ - "Navionics charts include an "Xplain" feature. This is a plain-language description that, with just a click of your cursor, deciphers confusing navigational symbols into plain-languge everyone can understand."

I use Navionics, and basically what the above means is, line the cursor up on any symbol you're unsure of, click the question mark, and in the pop up it normally gives a description in plain English. It's particularly useful for light colours and flash sequences. I'm not sure if it offers more information about spot-depths but it does give more info about most things.

 

[Keith-i]

Thanks, but it doesn't tell me anything for the depth numerals.

 

[pteron]

From the Navionic FAQ - "Navionics charts include an "Xplain" feature. This is a plain-language description that, with just a click of your cursor, deciphers confusing navigational symbols into plain-languge everyone can understand."

I use Navionics, and basically what the above means is, line the cursor up on any symbol you're unsure of, click the question mark, and in the pop up it normally gives a description in plain English. It's particularly useful for light colours and flash sequences. I'm not sure if it offers more information about spot-depths but it does give more info about most things.

But the explanation is often wrong! They appear not to be able to deal with multi coloured lights - take La Vielle for instance (off the Raz de Seine). It is [OC(2+1) WRG 12S 18M] but the explanation says it is "Green occulting light with a period of 12 seconds and a range of 14 miles" plus two other descriptions for the red and white sectors.

 

[scotts_mist]

Wow - that underlines the need to ensure its not the only means of navigation.

 

[prv]

But the explanation is often wrong! They appear not to be able to deal with multi coloured lights - take La Vielle for instance (off the Raz de Seine). It is [OC(2+1) WRG 12S 18M] but the explanation says it is "Green occulting light with a period of 12 seconds and a range of 14 miles" plus two other descriptions for the red and white sectors.

This is exactly why I prefer to navigate off paper charts that have been drawn and checked by a human being, rather than being assembled on the fly by a machine.

Pete

 

[pteron]

The light characteristics were correct on the chart - just the description is weird.

So if you are capable of reading the characteristics from a paper chart you'll be fine reading them from the chart on the ipad.

Overall, I was really impressed with the navionics software, the difference in intuitive usability between it and the raymarine plotter on board was night and day.