Cell phones at seaNov 19, 2008
To the editor: Does it make sense to rely on a cell phone as a serious part of an offshore voyaging vessel’s communications equipment? There is no question that cell phones provide convenient, private communications, but what about the use of cell phones by boat owners for emergency communications?
For a time, beginning in the early 1990s, cell phone service providers offered a special code feature (*CG) in some areas that would provide direct access to a U.S. Coast Guard operations center — provided you were within range. However, as providers moved from analog to digital systems, some did not continue the *CG feature, resulting in a confusing patchwork of service that contributed to significant delays in the Coast Guard response.
Also contributing to the confusion and hampering Coast Guard response efforts was the fact that many, if not most of these callers could not provide an accurate location, could not communicate with the rescue craft, and in some cases, the phone’s batteries died before they could complete the call. In one case, Coast Guard watchstanders received a call from a disabled 16-foot ski boat near the Texas City, Texas, dike about 6:00 p.m. The boat owner reported that his boat was disabled and anchored about a quarter mile (1,320 ft.) from the dike. After an hour into the search the owner could no longer be reached on the cell phone. Around 12:00 p.m. a passing tug reported sighting “a disabled boat near light 48 in the Houston Ship Channel,” (about 10 miles north in Galveston Bay) and the rescue was affected.
Another very significant factor, according to Capt. Gabe Kinney, then head of Coast Guard search and rescue operations, in a March 2000 article in BoatUS magazine, the biggest downside of using a cell phone to call for assistance is that “You’re calling the Coast Guard alone. But when you’re on VHF channel 16 calling for help, other boaters in the area can hear you and answer too.” He went on to say, “Often, they are lots closer than a Coast Guard boat and can get to you more quickly. Good Samaritan boaters do a fair amount of rescues, but they won’t know you’re in trouble if they can’t hear you call for help.” That’s just as true today.
In October of 2006, the Coast Guard asked all cell phone service providers in states other than Alaska to remove the *CG feature as a method of requesting emergency assistance. All of the cell phone service providers in Alaska have the *CG feature available and routed to a single Coast Guard emergency line ensuring that calls are not missed and cannot be misdirected. The Coast Guard urged all boaters to use VHF-FM radio as their primary means of making distress calls and that if a cell phone is their only means of communication, the call should be directed to the nearest 911 operator. Be careful here though, the call could be answered in the hometown of the cell phone owner, hundreds of miles away!
Unfortunately it is not possible to be very definitive about cell phone coverage at sea. It depends on so many factors — topography, inherently low transmit signal power, line-of-sight limitations, etc. Another major factor, of course, is that most cellular systems are designed for land-based service. That’s where the most current and potential subscribers and revenues are. Even where cell towers are located on high hills and headlands, transmission is line-of-sight and may be blocked in coves, inlets and the backside of islands, creating gaps in the coverage.
As to how far off shore you can be and still make and receive phone calls or send emails, etc.; the limitation is not so much with the base station as it is with the cell phone itself. Let’s say you have a cell tower located on a high hill right at the shoreline with its signals directed right out to sea. A signal from the cell tower may — under optimum conditions — get out to 30-45 miles. If you don’t see the dreaded “no service” message on the screen, that means that the signal from the tower is reaching the cell phone, but your cell phone’s signal may not be able to reach the tower. This is where cell phone external antennas and booster amplifiers come in. A booster, such as Digital Antenna’s DA4000 PowerMax, is claimed to increase the usable range out to 50 or more miles when coupled with Digital Antenna’s 8-foot Trifecta combination (cellular, VHF and AM/FM) antenna.
Keep in mind that cell phones are, for the most part, not marinized — keypads and cases are not sealed, printed circuit boards are not conformally coated — so you will have to take some special precautions to keep it out of rain and spray.
Verizon Wireless has just recently introduced its G’zOne (Gee-Zee-One) cell phone designed for use in high-abuse environments. Verizon claims it is ruggedized to military standards for shock and vibration, dust, heat, cold, etc and fully waterproof; it can be submerged for a full 30 minutes and still remain completely functional. No reports from users yet, but worth looking into.
So, by all means, take your cell phone with you, just don’t rely on it for emergency communications, that’s for the VHF!
— Ev Collier is an electrical engineer, an avid voyaging sailor and powerboater and an amateur boatbuilder.
Cells and phones
Two things are critical to cellular telephone service 1) the reuse of a limited number of frequencies, and 2) low-power transmissions. The network configuration that makes these two things possible are geographic areas called cells. A cell phone service provider, given a geographic area in which to provide service, divides the area into a number of cells. A cell may be two to 10 miles in radius, depending on the topography (hills, valleys, tall buildings, etc), the population (number of actual and/or potential subscribers who reside in the cell) and the density of traffic in the area. The cell contains a base station with a tower, usually with three or more antennas mounted on it and pointing in different directions, plus the necessary transmitting and receiving electronics.
Each antenna, using a cone-shaped directional beam, — like a flashlight beam — transmits within the cell with limited power from a few watts to about 100 watts, depending on the size of the cell, to avoid interference with adjacent cells. The number of beams, their shape and direction are designed to achieve maximum coverage; however, some gaps and dead zones are inevitable — generally in unpopulated, untraveled areas. Cell phone transmit power is considerably lower, ranging from 0.001 watt when near a cell tower to a maximum of less than one watt. Different frequencies are used in adjacent cells, again, to avoid interference. Cells are kept small since small cells mean shorter transit times and more frequent release of frequencies for reuse.
As the cell phone moves toward the edge of a cell, the cell’s base station detects its diminishing signal strength. At the same time, the base station in the cell toward which the phone is moving, detects its increasing signal strength. The two base stations coordinate with each other through the carriers Mobile Telephone Switching Office and at some point the cell phone receives a signal on its control channel telling it to change frequencies. This handoff switches the cell phone to the new cell.