Why EPIRBs Sometimes Struggle to Get a GPS Fix

Key Takeaways: An EPIRB that takes longer than expected to get a GPS fix is usually dealing with a cold start, poor antenna exposure, or rough sea conditions that keep the antenna dipping below the surface. Older chipsets and tired batteries can add more delay. Most modern GNSS equipped units should lock within a minute or two, but it is perfectly normal for some beacons to take longer when the sky view is compromised.

Why GPS Acquisition Can Be Slow
How Antenna Orientation Affects the First Fix
The Role of Battery Condition
Environmental Factors That Slow Acquisition
Cold Starts Versus Warm Starts
What You Can Do to Improve Performance
What Sailors Often Miss
Summing Up

Why GPS Acquisition Can Be Slow

When an EPIRB is first activated, it has to work from scratch. The internal receiver needs to download satellite data, identify which satellites are in view, and calculate its first position. If the beacon has been stored for months, the almanac and ephemeris data will be out of date, forcing a full cold start. That alone can add a minute or two.

The next hurdle is the sky view. A GPS antenna needs a reasonably clear hemisphere above it. If the beacon is floating upright in a seaway, the antenna may be exposed one moment and underwater the next. Every time it dips below the surface, the receiver loses signal lock and has to start again. Even heavy spray can degrade the signal enough to slow the process.

Older EPIRBs with early GPS chipsets simply do not acquire as quickly as modern multi constellation receivers. A new GNSS unit can use GPS, Galileo, and sometimes GLONASS, giving it far more satellites to work with.

How Antenna Orientation Affects the First Fix

The antenna on a floating EPIRB is designed to stand upright, but that does not guarantee perfect performance. If the beacon is lying on its side in a raft or wedged against gear, the radiation pattern becomes distorted. A poor angle reduces the number of satellites in view and increases the time needed to get a fix.

Even on deck, a beacon can struggle if it is too close to metalwork. Stainless rails, davits, and radar arches can all mask parts of the sky.

The Role of Battery Condition

A battery that is approaching the end of its service life may still pass a self test, but that does not mean it is performing at its best. Cold conditions and the heavy current draw during the first minutes of operation can expose weaknesses. If the voltage sags, the GPS receiver may behave erratically or take longer to stabilise.

This is one reason why manufacturers insist on fixed service intervals rather than “use until it fails”.

Environmental Factors That Slow Acquisition

Several conditions commonly reported by sailors can add delay:

Breaking seas that repeatedly swamp the antenna

Heavy rain or spray reducing signal strength

High latitude cruising where satellites sit lower on the horizon

Dense cloud cover which, while not a major obstacle, can add marginal delay

None of these will stop a beacon from working, but they can stretch the time needed for the first fix.

Cold Starts Versus Warm Starts

A cold start is the worst case scenario. The beacon has no recent satellite data and must rebuild everything from scratch. A warm start, by contrast, uses stored information to speed things up. Some modern EPIRBs periodically refresh their internal data during self tests, which helps reduce acquisition time.

If your beacon is more than a few years old, it may not have this feature.

What You Can Do to Improve Performance

There are a few simple steps that can make a noticeable difference:

Give the antenna the clearest sky view possible

Keep the beacon upright whether in the water or in a raft

Avoid placing it near metalwork if activated on deck

Replace batteries on schedule rather than stretching intervals

Consider upgrading if your unit is more than ten years old

None of these guarantee a fast fix, but they reduce the chances of unnecessary delay.

What Sailors Often Miss

How GNSS Constellations Change Performance

Modern beacons that use multiple constellations have a clear advantage. More satellites mean more chances to get a fix even when the sky view is poor. Owners of older GPS only units often underestimate how much this affects acquisition time.

The Impact of Storage Location

A beacon stored in a damp lazarette or near metal bulkheads may have degraded internal components long before it is activated. Moisture ingress, even at a microscopic level, can affect the GPS receiver.

The Effect of Liferaft Canopies

Some liferaft canopies are surprisingly effective at blocking satellite signals. A beacon inside a raft may take longer to acquire a fix than one floating freely outside.

Why Self Tests Do Not Predict GPS Performance

A self test checks power output and basic function, but it does not simulate a cold start or a compromised sky view. Sailors often assume a passed test means perfect performance, which is not always the case.

Need help deciding which EPIRB suits your boat and your budget?
Click here to see my recommended models and comparison table.

Summing Up

A slow GPS fix is usually the result of cold starts, poor antenna exposure, or rough conditions rather than a faulty beacon. Modern GNSS units are far quicker than older models, but even the best beacon can struggle if the antenna keeps dipping below the surface. Understanding these limitations helps set realistic expectations and highlights when an upgrade might be worthwhile.

This article was written by Dick McClary, RYA Yachtmaster and author of the RYA publications 'Offshore Sailing' and 'Fishing Afloat', member of The Yachting Journalists Association (YJA), erstwhile member of the Ocean Cruising Club (OCC) and owner/administrator of 'Liveaboard Sailboats for Sale'.