Many sources of advice for boats carry the legend "Not for Navigation" or sometimes "For reference only".
They often state that the relevant Hydrographic Office chart should be used for navigation. That is reasonable if the HO chart is up to date. But often the chart contains a warning such as "These channels are liable to frequent change and there may be less water than charted". Often the date of survey which is given is decades ago.
So directing users to the HO chart is actually useless in this case. That is why "Not for navigation" information from the web is often extremely valuable and very helpful.
So in such cases (mostly where there are shifting sandbanks) the HO charts should be labelled "Not for Navigation" and the up to date web information should be labelled "helpful for navigation".
I understand that people giving "helpful for navigation" information do not want to be held responsible .. which is why the disclaimer is included. But it does make a mockery of the true situation.
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