how to read a marine chart

[lanerboy]

ok i have just bought memory map marine charts for the uk as a starting block, now i know nothing about these charts (until i get myself booked on the appropriate courses) i was just wondering what all the numbers mean

i pressume the main numbers are the depths of the water in metres according to the scale but there are also small numbers next to each larger number which are a lower ammount

can someone please explain to me what all these numbers are for

i know some of you will think what a dick for asking such a silly question and think i possibly shouldnt even be getting a boat untill i understand all this but we all have to start somewhere

 

[sarabande]

have you worked your way through this site ?

http://mapserver.mytopo.com/mapserver/nautical_symbols/contents.html

and this is also a good one:-

http://www.sailtrain.co.uk/navigation/charts.htm


Would you not be better off asking if someone here could spend a day with you going through the basics on board ?

 

[hlb]

Never heard of memory map, so I'm not going to try to explain it.

All makes of charts are slightly different and we would be foolish to give information from here.

 

[lisilou]

ok i have just bought memory map marine charts for the uk as a starting block, now i know nothing about these charts (until i get myself booked on the appropriate courses) i was just wondering what all the numbers mean

i pressume the main numbers are the depths of the water in metres according to the scale but there are also small numbers next to each larger number which are a lower ammount

can someone please explain to me what all these numbers are for

i know some of you will think what a dick for asking such a silly question and think i possibly shouldnt even be getting a boat untill i understand all this but we all have to start somewhere

Take a close up pic of the screen and post it on here. I totally get why you want to ask the questions on here while you wait to do your course/s so as far as I'm concerned...ask away. (I can always learn from it too lol)
L

 

[prv]

i pressume the main numbers are the depths of the water in metres according to the scale but there are also small numbers next to each larger number which are a lower ammount

The big number is how many metres, the small number is tenths. So 76 means 7.6 metres. A decimal point would be easy to miss.

Pete

 

[lanerboy]

have you worked your way through this site ?

http://mapserver.mytopo.com/mapserver/nautical_symbols/contents.html

and this is also a good one:-

http://www.sailtrain.co.uk/navigation/charts.htm


Would you not be better off asking if someone here could spend a day with you going through the basics on board ?

Thanks great sites them i will have a good look at both

Yes i may ask for help once my boat is in the water approx 4 weeks from now but just tring to get a head start

 

[lanerboy]

The big number is how many metres, the small number is tenths. So 76 means 7.6 metres. A decimal point would be easy to miss.

Pete

Thanks prv i see now

 

[hlb]

The big number is how many metres, the small number is tenths. So 76 means 7.6 metres. A decimal point would be easy to miss.

Pete

Yep, but for all we know, that might be a drying hight and not the depth.

Dowe really want to risk it??

 

[lanerboy]

Yep, but for all we know, that might be a drying hight and not the depth.

Dowe really want to risk it??

I knew someone would try and make it difficult

 

[VicS]

I knew someone would try and make it difficult

Drying heights are underlined ( at least they are on paper charts) So 21 means dries 2.1m above chart datum

 

[grumpy_o_g]

Whilst different publisher's chart are all slightly different you can get a copy of Admiralty Chart 5011, which is actually a booklet with all the chart symbols, etc. in or you can get a copy of this: http://www.amazon.co.uk/How-Read-Nautical-Chart-Abbreviations/dp/0071376151. I wouldn't call it readable but it's better than AC 5011 because it actually explains what the numbers, etc. mean. Throw in a couple of good books on basic navigation, etc. and you're halfway there. If you're at SIBS have a browse round the Kelvin Hughes stand and see if there's anything that works for you.

p.s. the dicks are the ones who don't ask the questions and end up calling 999 from a mobile phone with virtually no battery from a very cold little boat on a very dark night with absolutely no idea where they are.

 

[Solitaire]

The big number is how many metres, the small number is tenths. So 76 means 7.6 metres. A decimal point would be easy to miss.

Pete

This is only half the story! The numbers on the charts do not represent depth of water. They show soundings below chart datum. To get depth of water you then need to know the height of tide at any given time. So if the height of tide is say 3.5 metres at the point assumed in your example, then depth of water would be 11.1 metres.

 

[Wiggo]

This is only half the story! The numbers on the charts do not represent depth of water. They show soundings below chart datum. To get depth of water you then need to know the height of tide at any given time. So if the height of tide is say 3.5 metres at the point assumed in your example, then depth of water would be 11.1 metres.

Or you'd be 4.1m above the water, if it was a drying height.

Or if it was a bridge clearance, you'd need to know the height of MHWS...

 

[tico]

Wait for it!
Chart datum.... height (how deep the water is) at lowest tide , ie at the very lowest on a big spring tide.
(yes I know thats not strictly true, but it's close enough)
Thus the figures are related to that level.
so.. when the chart gives a depth of 2 metres, you add the amount of tide to give the predicted actual depth.
So... the chart says 2 metres, the tide tables give a high tide of 3.5metres (also related to chart datum)... the resulting depth at high tide would be 5.5 metres.
OK?
Suggest that you read some basic reading matter on navigation first to give a good grounding (sorry!) in the subject

 

[mikemanor]

Or if it was a bridge clearance, you'd need to know the height of MHWS...

No - on Admiralty and Imray charts bridge clearances are given from HAT not MHWS.

 

[mikemanor]

Essential Navigation and Seamanship Course

For the OP, I would recommend that you start with the RYA Essential Navigation and Seamanship Course. This is an online course that you can do in your own time at your own pace. It is provided by many RYA teaching establishments who will give telephone/email support if you need it.

Google it to find the best price.

 

[PaulGooch]

Some basic info here : http://chartwork.co.uk/Cadets/Resources/Charts.pdf

 

[Grimslion]

for reading a marine chart you can locate to the following link
http://mapserver.mytopo.com/mapserve.../contents.html
here you will get all the procedures to read the maps and other things

 

[lanerboy]

for reading a marine chart you can locate to the following link
http://mapserver.mytopo.com/mapserve.../contents.html
here you will get all the procedures to read the maps and other things

link not working

 

[Solitaire]

Or you'd be 4.1m above the water, if it was a drying height.

Or if it was a bridge clearance, you'd need to know the height of MHWS...

I did not intend to do a full scale tidal post. . And has already been stated bridge clearance is HAT