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Maritime Information

On 20 January 2015 the Coast Guard declared Sea Area A1 in certain areas off the coast of the United States based upon the performance of the Coast Guard's Rescue 21 System in accordance with applicable provisions of the International Convention for the Safety of Life at Sea, 1974 (SOLAS). The Coast Guard defines Sea Area A1 as those areas where more than ninety percent of the area within 20 nautical miles seaward of the territorial baseline along the East, West and Gulf Coasts of the United States, excluding Alaska, and including Hawaii, Puerto Rico, Guam, the Virgin Islands of the United States and the Northern Mariana Islands of Saipan, Tinian and Rota, is within coverage of Coast Guard very high frequency, or VHF Coast Stations that provide both a continuous watch for Digital Selective Calling, or DSC, distress alerts on Channel 70 and a capability to respond to distress alerts.

The Coast Guard operates a network of VHF transceivers and antenna high-sites which are remotely controlled by Sector communications centers to provide coverage extending out to at least 20 nautical miles from shore, and often much further. Coverage is reasonably continuous through most of the Atlantic, Gulf and Pacific Coasts, the Great Lakes, and many rivers. Many urban areas of the U.S. are also covered. This system serves as:
  • the primary means for mariners to contact the Coast Guard in a distress - over 12,000 distress calls are received yearly over this system
  • the primary means for broadcasting urgent marine information to mariners, and
  • a command and control system for Coast Guard and other vessels.
Of the 25 largest U.S. cities ranked by population in the 1990 census by the Department of Commerce Census Bureau, 19 cities, i.e. 76%, are close to navigable waters and are within at least partial coverage of the U.S. Coast Guard’s VHF distress system.
Each Rescue 21 site consists of receivers guarding VHF Channels 16 and 70, the maritime radiotelephone and digital selective calling distress, safety and calling channels respectively, and  transceivers capable of operating on other channels, including Channel  22A used for urgent marine  information broadcasts and broadcast notices to mariners.
The Rescue 21 system is Global Maritime Distress & Safety System-compatible and will provides  GMDSS Sea Area A1 capability once declaration is made.


These charts are provided to give mariners guidance of locations where VHF calls to the Coast Guard may be expected to be heard.  It is also provided to give commercial fishing industry and other regulated commercial vessel operators guidance of locations where carriage VHF radiotelephone equipment may be sufficient.  Operation outside these areas may require carriage of such long range communications equipment as HF radiotelephone or satellite communications terminals in addition to VHF radiotelephone equipment.  See 46 CFR § 28.245   and 47 CFR Subparts R, S and W for further information.

VHF Distress Coverage Charts

Charts showing predicted areas of VHF  coverage from shore can be downloaded in .jpg format. As indicated on the charts, coverage plots assume a mobile transmitter power of 1 watt with an antenna two meters above water level.

Except as noted, these coverage charts depict the actual Sea Area A1 in theUnited States.

Click on the image below to view full-sized map.

 Rescue 21 Plot for United States of America

Coast Guard Sector Rescue 21 images sorted by Coast Guard District

Black lines on the images represent sector boundaries.  You may control the size of the image in your browser by pressing your Ctrl key while scrolling your mouse wheel up or down.

First District

Fifth District

Seventh District

Eighth District

Ninth District

Eleventh District

Thirteenth District

Fourteenth District

Seventeenth District

Revised: 01 July 2016