Reposted from Marine Electronics Journal
RTCM 13200.0 standard 2 color SOS eVDSD testing to IEC 60945 Section 8.7.2 "Vibration"
The pyrotechnic flare has been used in some form for centuries to indicate a vessel in distress. A 1979 Coast Guard regulation required recreational boats operating on the high seas of the U.S. to carry visual distress signals. The pyrotechnic flare, which had been required on commercial vessels for many years, was the most effective option but there are concerns about the safety of flares and the difficulty involved in properly disposing of expired pyrotechnics.
The Coast Guard rules do provide for a non-pyrotechnic replacement – an orange flag with a black ball and square for daytime use, and a battery-operated flashlight or lantern with an automatic S-O-S function for nighttime use. Over the years several manufacturers have offered directional beam products built to meet the Coast Guard S-O-S light regulation. These have not proved to be particularly effective, due to the directionality of the light and its white color which is easily lost among background lights.
In 2012, the Coast Guard Research and Development Center (RDC) completed a study which included lab tests, field demonstrations, and ergonomic tests of a selected group of non-pyrotechnic signal devices, with the objective to identify the characteristics that make them detectable and attention-getting. Prior to this study, the RDC had conducted a Functional Requirements Workshop, issued a Request for Information (RFI), and performed extensive market research to determine candidate signal devices.
Among the signals tested, LED devices consistently outperformed devices using flashtube or incandescent technology. This is due to the higher effective intensities presented by the LED devices as compared with incandescent and flashtube devices with comparable power sources. White and red signal colors with moderate to rapid flash rates were preferred by test observers. The study set the stage for more work on determining the most effective color, flash rates, and flash patterns.
Using the RDC report as a starting point, RTCM established Special Committee 132 in March 2013 to address the need for an improved technical standard for electronic visual distress signal devices (eVDSD) that would improve on existing standards and leverage advances in LED technology. The goal was to create a signal that was more effective, with superior visual conspicuity, extended operational time and reduced environmental risks. The Coast Guard RDC put together a plan of laboratory and field tests to establish the best combination of characteristics for a new eVDSD.
In the meantime, Sirius Signal introduced in 2014, an “interim” handheld S-O-S distress light for boats using white LEDs. It differed from the directional beam light as it displayed light over an arc of the horizon with both horizontal and vertical planes. It served as a bridge for the design of the new generation of lights being developed using the RDC work.
The RDC completed laboratory tests in April 2014 and field tests in Long Island Sound in September 2014. The purpose was to evaluate human subject response time with respect to colors, intensities, and signal timing characteristics. On four nights, testing over water with different background lighting environments included off-the-shelf devices including hand-held pyrotechnic flares as well as programmable LED test panels. Blue flashing LEDs were the most easily detected and received the highest rating. But flashing blue lights are reserved for emergency vehicles under national and international rules. So the preferred color for eVDSDs evolved to cyan as the color closest to blue but distinct from it. It was also apparent from the testing that optimal conspicuity would include at least two colors to differentiate from any other light characteristics visible in the maritime, nighttime environment. A unique flashing pattern along with unique colors would also be needed so that the signal would not be confused with other flashing lights in the marine environment. The light would also need to be an all-around pattern so that boaters in distress would not need to aim the device. Ultimately, the study recommended cyan (505 +/- 15 nm) and red-orange (610 – 620 nm) LED lights, in an alternating-color pattern, in groups of three to four flashes per group. Additionally, with increasing reliance on night vison devices for search and rescue, it became apparent that an infrared component at 770-890 nm should be included — an important feature not included in the 1979 regulation.
As work proceeded, it became apparent that the color of the lights could significantly affect cost because each LED color requires a specific chemistry. More common colors are less expensive, so the cyan color was slightly adjusted to 490-520 nm.
In June 2018, using the foundational work by the Coast Guard RDC, SC132 completed its work and RTCM Standard 13200.0 for eVDSDs was published. The RTCM standard specifies an unique two-color (red-orange/cyan) Morse Code S-O-S signal (● ● ● — — — ● ● ●) visible at a range equal to or greater than the visual range of a 500 candela hand-held flare at night. The “S” elements are red/orange and infrared, and the “O” elements are cyan and infrared in a repeating 3.5 second period. The device is accepted by the Coast Guard as meeting the nighttime visual distress signal requirement.
This innovation addresses both safety and environmental concerns while enhancing the effectiveness of distress signaling at sea.
Further adoption of RTCM Standard 13200.0 first took place in Canada in 2020. Australian states Tasmania and western Australia also followed with the remaining Australian states currently evaluating potential adoption. ACR, Ocean Signal, and Wescom have announced their entry into the RTCM S-O-S two color eVDSD market, following Sirius Signal, which was first to market in 2019. This provides boaters with multiple purchase options for carriage.
After review of the U.S. Coast Guard Research and Development Center Report, “Daytime Distress Signal Effectiveness,” the RTCM SC132 committee concluded additional testing is needed to compare the RTCM Standard 13200.0 SOS eVDSD to a handheld 500 candela flare for daytime use. The committee has interest from Sirius Signal, ACR, and Wescom to furnish their products for testing. Once the test is complete, if it can be proven the RTCM Standard 13200.0 SOS eVDSD can be as easily seen during the day as a 500-candela flare, the committee will seek the Coast Guard’s acceptance of this standard as both a night and day device.
Please contact Anthony Covelli, RTCM SC132 Chairman (rtcmchairsc132@gmail.com), if you would like to join and participate in the ongoing work at RTCM.
Anthony Covelli is CEO of Sirius Signal and Chair of RTCM Special Committee 132, Electronic Visual Distress Signaling Devices.
Bob Markle is retired from the US Coast Guard, Past President of RTCM and a member of its Board of Directors, and owner of Markle Marine Safety Services LLC.