how to read a marine chart

[prv]

Or if it was a bridge clearance

Bzzt - bridge clearances *do* use a decimal point, presumably to keep them from being confused with nearby depths. See the Northam Bridge near the top of this chart. So the OP's small and large number is not a bridge.

Pete

 

[prv]

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

In which case the big number is still metres, the small number is still tenths, and my post is still correct

(Good idea to point it out to the OP nonetheless)

Pete

 

[henryf]

I do hope the OP is not put off by all this willy waving.

In amongst the sea of confusion are a couple of good responses.


The smaller number is tenths of a metre.

A line underneath the number indicates it is a drying height ie. you would be above the waterline by that amount.

All heights are taken from chart datum. For the actual situation you would need to add the height of the tide for that date and time to the numbers shown on the chart. This would explain how it may be possible to cross areas shown as drying on the chart in your boat depending on your draught.

As has been suggested there are a number of sources to learn more and I couldn't recommend strongly enough that you go down that route. The best method would be to read up yourself and then spend time with a real person who can answer any questions and put everything in context.

In the meantime this forum is a treasure chest of knowledge should you have cause to use it.

Henry

 

[Wiggo]

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

Yup, my bad! Think before posting.

Still, if you work of MHWS not HAT, at least you won't have to worry about ducking...