"What we've got here is a failure to communicate." The famous line from the 1967 film "Cool Hand Luke" accurately describes the root cause of many marine mishaps. Recognizing this, efforts have been made over the years to improve communications.
While underway or at anchor, we are required to monitor VHF-FM channel 16, the international call and distress frequency, except when participating in a Vessel Traffic Service system, in which case the Coast Guard monitors channel 16 for us. However, search-and-rescue authorities learned long ago that compliance with this requirement is spotty. It is unwise to assume that Channel 16 is always being properly monitored, especially in busy areas loaded with recreational vessels that clutter the frequency with non-essential chatter. This has resulted in missed mayday calls. Digital Selective Calling (DSC) technology has been used for some time now to help overcome this problem and is a key component of the Global Maritime Distress and Safety System (GMDSS). It is now a standard on many marine radios.
The idea is relatively simple. Someone in serious trouble presses the red distress button on a DSC-enabled VHF-FM radio, which then broadcasts a distress alert over channel 70. Any DSC-enabled radio that picks up this data signal will sound a loud two-tone alarm and automatically switch over to channel 16 for voice communications between the vessel in distress and whoever may have received the call. Every DSC-enabled radio automatically monitors channel 70 in the background at all times, in addition to whatever voice channel you're on, so you can't forget. The shift to channel 16 is automatic, so there are no more missed distress calls.
Many of these DSC-enabled radios also permit interfacing with a GPS receiver that will broadcast position information as well. If you've ever heard the Coast Guard or an assisting vessel struggle to get accurate information from a boater or mariner in distress through a static-filled atmosphere, you can easily see the value of this feature. In virtually every conceivable way, DSC technology is a major advance in communications, but the Formidable Rule of Unanticipated Consequences (FRUC) can always crash the party.
