The BBC has advised that the midday shipping forecast will not be available from the Westerglen transmitter between 21st and 28th July 2015.
Engineers need to grease the stays and this requires the transmitter to be switched off.
The Burghead and Droitwich LW transmitters will be unaffected.
It is hoped that boaters served by the Westerglen transmitter may still be able to hear Radio 4 LW from the other two transmitters, although not as clearly, but this is not guaranteed.
Listeners will be reminded about the switch off in the days leading up to it.
It is possible to hear the 0048 and 0520 shipping forecast live by going to the Radio 4 homepage, clicking on 'listen live'.