There is no hard and fast rule for where "offshore" begins, but as you go further from the harbor, you will require more and more equipment to safeguard yourself. VHF radio range is usually between 25 and 50 miles, depending on antenna height and atmospheric conditions, so it is safe to say that more than 30 miles offshore, you may have trouble calling for help. An HH-65 helicopter can go about 90 miles offshore, an HH-60 can go about 150. If you go beyond that, you are certainly not beyond help, but it will take some creativity to get to you, and if you do travel well offshore, you should make sure you are equipped with long range communications equipment, survival gear, and DEFINITELY TAKE A 406 MHz EPIRB!
The world's nations are currently in the process of establishing the Global Maritime Distress and Safety System, or GMDSS. If you're curious about the details of GMDSS, click here. Put simply, distress notification, which has traditionally been via voice, is now becoming more and more via data. The traditional MAYDAY call is now more commonly replaced by EPRIB activation or a DSC transmission. If you're new to the open ocean, you're probably starting to wonder about some of these acronyms. We've already covered GMDSS. The next few paragraphs should help you through the rest of the alphabet soup of survival at sea.
EPIRB stands for Emergency Position Indicating Radio Beacon. It is a small device that transmits on a frequency of 406 MHz. A 406 MHz EPIRB, from here on referred to simply as a 406, can be either manually or automatically activated. Automatically activated EPIRBs will be set off either upon contact with seawater or upon removal from their storage bracket. Orbiting satellites will detect your beacon and relay the signal to stations on shore. The unique feature of 406s are that they transmit a coded signal as part of their transmission. As long as your EPIRB is properly registered, along with your position the Coast Guard will also get information about your boat. 406s also send out a weaker signal on 121.5 MHz. This is because most rescue craft use direction finders that tune to that frequency. The 406 signal will locate you to within a few miles, at which point rescue craft will home in on the 121.5 MHz signal to pinpoint you. If you take nothing else with you offshore, this device is a must.
DSC stands for Digital Selective Calling. DSC is replacing voice notification as the primary method for distress alerting. New VHF and HF radios are equipped with a special feature that sends a coded digital signal that includes a position, description of your vessel and brief summary of the nature of your distress. VHF DSC is not yet in widespread use in the U.S. and the Coast Guard has only limited monitoring capability. HF/MF DSC however, is monitored by all group operations centers and communications stations, and the system's long range greatly improves the chance of at least one station receiving your call.
AMVER stands for Automated Mutual-assist Vessel Emergency Response. It is a database managed by the U.S. Coast Guard that merchant ships check in with when they sail. It is mandatory for most U.S. flagged ships, and voluntary for everyone else. Happily, a large number of foreign vessels do choose to participate. When a distress is reported far out at sea, the Coast Guard can query its database to locate the nearest participating ship. Though we cannot compel a ship to divert from its track, instances where captains refuse are rare, and usually relate to safety concerns. Who wouldn't be reluctant to head into a storm that has already gotten someone else in trouble? The 11th District typically diverts about 1 AMVER participant a week, usually to search out the source of a distress signal. They have often proven to be the difference between life and death for someone in distress.
INMARSAT and IRIDIUM are satellite communications networks. Thanks to ever newer technology, these satellite telephone systems that 10 years ago were enjoyed only by the military vessels and billion dollar shipping lines are now within the reach of many boaters. Terminals are now sized and priced to equip even the smallest boats, and except for having to get used to a phone number with a few extra digits, making a phone call to or from the middle of the ocean is now as easy as ordering a pizza. Most terminals also act as teletypes, and will automatically receive telexes about the weather, Notices to Mariners, and broadcasts about other vessels in distress. Similar to a DSC system, they also have a distress function. These systems represent the leading edge of communications and should be considered by anyone planning a transoceanic voyage or who intends to operate routinely in the open ocean.