EPIRBs and PLBs Compared: Ocean Signal, McMurdo and GME

This is an independent, objective comparison — we have no partner among beacon brands. It is built from each maker's published specifications and the Cospas-Sarsat/AMSA standards, not a hands-on test. See our guide to EPIRBs and PLBs for the underlying system.

Every 406 MHz beacon from these three makers clears the same Cospas-Sarsat certification, so "will it raise the alarm" is settled at purchase. The engineering that separates them sits in five layers stacked on top of that baseline: the GNSS receiver that fixes your position, whether the unit is MEOSAR/Return Link capable, whether it carries integrated AIS for local homing, the LiMnO2 battery duty cycle, and the activation category and form factor. This piece works through each, with the real published figures and where the ranges genuinely diverge.

At a glance

GNSS receiver: what actually fixes your position

Both an EPIRB and a PLB embed their own GNSS receiver and encode the resulting latitude/longitude into the 406 MHz message. That encoded fix is what the Rescue Coordination Centre acts on, so the receiver's cold-start speed and weak-signal tracking matter more than the headline "has GPS" tick.

The generational split is stark. Legacy beacons ran 12–20 channel GPS-only front ends. The current units here run 66–72 channel multi-GNSS silicon: Ocean Signal's EPIRB2 uses a 72-channel receiver tracking GPS, Galileo and GLONASS; the McMurdo SmartFind G8 carries dual GPS + Galileo receivers; GME's MT600G/MT606FG pair GPS and Galileo behind a top-mounted quad-helix antenna with, per GME, "zero warm-up time". More constellations in view means more usable birds above the horizon from a beacon lying low in a swell with a fraction of the sky visible — the acquisition margin that decides whether the first 406 MHz burst already carries a valid position or a coarse one.

Published encoded-position accuracy from the beacon's own receiver sits around 100 m (Ocean Signal quotes accuracy to within 100 m; McMurdo's FastFind PLB quotes ~62 m). Either is a helipad-sized box versus the ~5 km class specification for a Doppler-only, GNSS-less alert — which is the practical case for choosing any GNSS beacon over a bare 406 unit. Among these three the receivers are close enough that constellation coverage and antenna design, not a metre or two of quoted CEP, are the real discriminators. The models that lose out are the GPS-only rescueME PLB1, FastFind 220 and GME MT610G — still fully capable beacons, but without Galileo they forgo both the multi-constellation acquisition margin and, by extension, Return Link.

MEOSAR and Return Link Service: the confirmation layer

This is the genuine 2020s differentiator and it is worth understanding at the system level. The Cospas-Sarsat space segment has moved from LEO/GEO to MEOSAR — SAR payloads riding the medium-Earth-orbit GNSS constellations, with Galileo's 24+ satellites as the backbone. MEOSAR resolves a GNSS-encoded 406 MHz alert in minutes; published demonstrations have taken alert-to-located under four minutes, against the one-to-four hours a Doppler-dependent LEOSAR pass could historically need. Any modern 406 beacon benefits from MEOSAR on the downlink whether or not it advertises it.

Return Link Service (RLS) is the piece you actively pay for, and it only exists because Galileo is bidirectional. Once the ground segment computes the position, it tasks the Galileo constellation to transmit an acknowledgement back down to the beacon, which the unit displays as a dedicated blue LED distinct from the transmit indicator. Functionally it does not speed up the rescue — SAR is tasked identically — but it closes the psychological loop that every skipper who has held a live beacon knows: the signal got out, the position is known. On a Melges 40 that has just filled and rolled, with the crew clipped-out and in the water waiting, that blue light is the difference between disciplined waiting and blind hope.

RLS is present on the Ocean Signal EPIRB2 and PLB3, the McMurdo SmartFind G8, and GME's MT606G/MT606FG. It is absent from the older rescueME PLB1, McMurdo FastFind 220 and GME MT610G, because RLS is a receive function that requires the Galileo receiver those units do not have. If confirmation-of-receipt is a decision criterion, it collapses the field to the multi-GNSS flagships and rules the GPS-only PLBs out on capability rather than price.

Integrated AIS: the terminal-homing layer

AIS on a beacon is a separate transmitter operating on the AIS SART channels (161.975 and 162.025 MHz, marine VHF, roughly 1–5 W) that broadcasts an active-SART message. Nearby chartplotters and AIS receivers render it as the SART cross symbol carrying the beacon's own identity, giving instant bearing and range on the very screens a race crew already watches. In a fleet, or with a coach boat/mother ship in company, this is the fastest possible localisation — seconds on your own display versus any satellite geometry.

The hard limit is that AIS is VHF line-of-sight and is not detected by satellite. Realistic range is a few nautical miles to a masthead antenna, less to a handheld. So integrated AIS is a complement that shines in exactly the crewed, in-company environment a Grand Prix regatta creates, and does nothing on its own for an isolated offshore incident — which is precisely why it is layered on top of 406 MHz and never instead of it. AMSA also lets you register the AIS identity alongside the beacon HEX ID, which is worth doing.

AIS-equipped models here are the Ocean Signal EPIRB2 and PLB3, the McMurdo SmartFind G8 AIS, and GME's MT606/MT606FG. Where McMurdo pulls slightly ahead on paper is the G8 AIS pairing AIS with an infra-red (night-vision) locating light alongside the standard high-brightness LED — a covert homing aid for SAR assets on NVGs that the others in this set do not list.

Battery: chemistry, duty cycle and the two numbers that matter

All three build on lithium manganese dioxide (LiMnO2) primary cells, chosen for flat discharge, very low self-discharge and cold performance — the reason a decade-long shelf life and reliable output at -20 °C are achievable in a sealed, non-serviceable pack. Two distinct figures follow from it and buyers routinely conflate them.

Storage (shelf) life is the replacement-by date stamped on the unit: 10 years across the EPIRBs here (Ocean Signal EPIRB1/EPIRB2, McMurdo SmartFind G8, GME MT600G/MT606FG), against ~7 years on the GME MT610G and ~6–7 years on the Ocean Signal PLBs (PLB1 7-year, PLB3 6-year). Operating life is guaranteed continuous transmit time once activated: ≥48 h for the EPIRBs and ≥24 h for the PLBs, and note both are specified at -20 °C, the worst-case where cell capacity bottoms out — warm Australian water will yield more. The EPIRB-versus-PLB gap is purely pack size driving a higher sustainable 406 MHz transmit duty cycle, not a difference in chemistry between the brands.

Practically, this is a genuine cost-of-ownership line, not a footnote. Replacement is a factory or authorised-dealer battery service, not a user cell swap, so the shelf date is a scheduled, paid maintenance event. It belongs on the safety audit with the expiry tracked, because an out-of-date beacon is a non-compliant beacon regardless of how well it would still transmit.

Activation category and form factor

For an EPIRB the decisive engineering choice is activation category. A Category 1 unit sits in a hydrostatic-release housing that mechanically ejects the beacon at a submersion depth of 1–4 m; the beacon then floats free and self-activates on water contact — the only configuration that protects you in a fast rollover or downflooding where nobody can reach it. A Category 2 is manual-only and depends on a crew member deploying it. On a boat that can invert and fill quickly, Cat 1 float-free is the defensible choice for the vessel EPIRB. All three makers field Cat 1 float-free AIS/RLS units: Ocean Signal EPIRB2 Pro (and EPIRB1 Pro), McMurdo SmartFind G8 in its automatic housing, and GME's MT606FG.

PLBs are manual-only by design — there is no float-free PLB — and are judged instead on carry-ability, because the entire point is one registered beacon per crew member, on the person, that goes overboard with them. Here Ocean Signal's rescueME PLB1 is the class benchmark for size: 116 g at 77 × 51 × 32.5 mm, small enough to sit in a lifejacket without notice. The trade-offs are visible in the spec sheet: the PLB1 is GPS-only with a 7-year battery, whereas the larger rescueME PLB3 buys AIS, RLS and NFC in a taller 200 mm-tall body with a 6-year battery. GME's MT610G answers with a compact, inherently buoyant, IP68, Australian-made PLB (7-year battery, 72-channel GPS, solid-state light), and McMurdo's FastFind 220 is a capable compact PLB but, importantly, one without RLS. The professional call is whether per-crew AIS/RLS justifies the bulk of a PLB3-class unit, or whether the smallest reliable beacon that will actually be worn every race — the PLB1 — is the better real-world outcome.

NFC, homing and the practical extras

Two secondary layers round out the comparison. Every unit carries a 121.5 MHz homing transmitter (Ocean Signal quotes 50 mW nominal on the EPIRB1) for final VHF direction-finding by aircraft and SAR craft, plus a high-intensity light — solid-state strobe on GME, LED on Ocean Signal, and McMurdo's LED-plus-IR pairing on the G8. NFC appears on the newer Ocean Signal units (PLB3, EPIRB2), letting a phone app read battery state, self-test history and programming without breaking the housing seal — a real maintenance convenience that shortens pre-season checks, though it has no bearing in an actual emergency.

On support, GME is the one genuine local differentiator: it is the only Australian beacon manufacturer, designing and building EPIRBs and PLBs in Australia for over 30 years, its units built to AS/NZS 4280.1 as well as Cospas-Sarsat Class 2. For an Australian campaign that values in-country service, spares and battery servicing, that is a substantive advantage rather than a marketing line — provided the specific model also carries the GNSS/RLS/AIS capability the boat actually needs.

Our take

Judged on engineering rather than reputation, the three separate cleanly by layer. If integrated AIS plus covert IR homing on the vessel EPIRB is the priority — the most complete SAR signature in this set — the McMurdo SmartFind G8 AIS is the best-equipped EPIRB. If smallest reliable per-crew carry is what actually gets a beacon onto every sailor, the Ocean Signal rescueME PLB1 is unmatched at 116 g, with the PLB3 as the step-up when you want AIS and RLS on the person. If Australian-made with local servicing in a Cat 1 float-free AIS/RLS package matters, GME's MT606FG delivers it without a capability compromise. All of them clear Cospas-Sarsat; the choice is which of the five layers above your program weights most.

The non-negotiables are identical whichever you pick: register the HEX ID (and any AIS identity) with AMSA, keep the LiMnO2 battery in date via factory service, choose Cat 1 float-free for the vessel EPIRB, and carry a per-crew PLB overboard. It is the top line on the safety audit; see also race yacht safety systems.

Our pick: there is no single winner because all three are certified to the same standard — the decision is layer-driven. For the best-equipped vessel EPIRB (AIS + IR + RLS), the McMurdo SmartFind G8 AIS; for the smallest crew PLB that will genuinely be worn every race, the Ocean Signal rescueME PLB1 (or PLB3 for on-body AIS/RLS); for an Australian-made Cat 1 float-free AIS/RLS EPIRB, GME's MT606FG. Register with AMSA, keep the battery in date, and carry it right.