ECDIS No Overlay
Where there is no ADMIRALTY paper chart at an equivalent scale to the ENC, UKHO is not able to compare coverage and add additional information. In these areas, the AIO shows a grey-hatched polygon labelled ‘No overlay’.
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Most ECDIS provide a button within the settings menu. This can be switched on/off as per convenience. Although it is strongly recommended to keep it ON during voyage monitoring so that the duty officer is aware about this anomaly.
ADMIRALTY paper T&P NMs may occasionally display within a ‘No overlay’ polygon if the information has been published for smaller scale paper charts and is also relevant at a larger scale. Additional information, such as local T&P NMs, may be available in these areas from other sources. When navigating in these areas, seafarers should ensure that other sources of information such as local web sites, Navtex, port notices etc have been consulted.