Why Your Yacht Might Be a “Ghost Ship” to AIS

You’ve installed the latest transponder, the icons are moving on your screen, and you feel safe. But, there is a silent epidemic in the cruising community: The Stealth Yacht.

Many of us are transmitting an AIS signal so degraded by hardware choices that we’ve essentially become invisible to the big ships we’re trying to avoid.

If you want to ensure you aren’t just “whispering into the wind,” here is how to audit your AIS health from the nav station to the masthead.

Power Paradox: Watts vs. Reality

Most Class B units are rated at either 2W or 5W. On paper, that suggests a visibility range of up to 20 miles. In reality, your AIS signal is like water in a leaky hose. By the time it travels from the transponder, through the splitter, up the mast, and out the antenna, that 5W “blast” can be reduced to a fraction of a watt.

If a ship only sees you at 3 miles, they don’t have enough time to adjust their course. You aren’t just looking for any signal; you’re looking for efficient signal.

Benchmarking Test: Who else is there?

Don’t trust your own screen to tell you if you’re being seen. Use a shore-based aggregator like MarineTraffic or VesselFinder for a real-world audit:

• The Peer Review: Find a yacht similar in size to yours within a 5-mile radius. If their track is a solid line and yours is a stuttered series of “lost” positions, your transmission hardware is failing you.
• The Blackout Zone: If all boats disappear at once, it’s a lack of shore-side receivers. If only you disappear while offshore, your signal is likely “suffocating” before it leaves the boat.

The “Clog” in the system: Cable & corrosion

The most common culprit for a weak signal is the coaxial cable. Many production boats come standard with RG-58—a thin cable that is notorious for signal “leakage” over long runs.

Performance Ratings for Mast-Run Cables

Cable Grade	Signal Loss (per 100ft)	Recommendation
Aircell 7	Very Low	The Best Choice. Flexible and high-performance.
LMR-400	Lowest	Elite. Harder to install due to stiffness, but unparalleled.
RG-213	Low	Solid. Bulky and heavy, but very reliable.
RG-58	High	Avoid. At 50 feet, you lose nearly half your transmit power.

Pro Tip: Look for Tinned Copper or Marine Grade labels. Standard copper wire reacts with salt air to create “Black Wire Disease,” an oxidation that increases resistance and kills your signal within months.

The Splitter: Choosing your “Traffic Cop”

Sharing one antenna between your VHF radio and your AIS is common, but it requires a high-quality “traffic cop” to manage the signals.

• Passive Splitters (The Budget Trap): These simply divide the incoming energy. You lose half your signal strength immediately. Worse, they offer poor protection against the 25W surge of your VHF, which can eventually damage your AIS circuitry.
• Active “Zero-Loss” Splitters: Units like the Digital Yacht SPL2000 or Vesper SP160 use internal amplification. They ensure that even though the antenna is shared, your AIS gets 100% of the signal power it needs.

Canary in the Coal Mine: Your VHF radio

Your AIS and VHF usually share the same “highway” (the cable and antenna). If your AIS is weak, your radio is almost certainly compromised too.

If you notice your VHF reception is “scratchy” or people often ask you to repeat your transmissions, your AIS is likely struggling. Fixing your cabling isn’t just about being a dot on a map, it’s about ensuring your emergency radio call actually reaches the Coast Guard when it matters most.

Digital Stethoscope: ProAIS2

To move from guesswork to data, use the ProAIS2 diagnostic software. Since most AIS manufacturers (Raymarine, Garmin, B&G, etc.) use SRT internal boards, this tool is the industry standard for troubleshooting.

The key metric is the VSWR (Voltage Standing Wave Ratio). This measures how much power is actually leaving the antenna versus how much is “bouncing back” into the radio:

• 1.1:1 to 1.5:1: You’re in the green. Your system is efficient.
• 2.0:1 or higher: You have a “blockage.” This usually points to a waterlogged antenna, a corroded PL-259 connector, or a failing splitter.
• Over 5.0: You’re toasting your AIS device.

Download ProAIS2: You can find the latest versions for Windows and Mac here.

Summary checklist for the offshore navigator

To help you effectively audit your system, here’s a summary checklist to use while assessing your AIS system.

• Audit: Compare your MarineTraffic track against nearby vessels.
• Hardware: Verify your cable isn’t standard RG-58.
• Integrity: Ensure all connectors are tinned, crimped, and sealed with adhesive heat-shrink.
• Equipment: Upgrade to an active splitter if you are currently using a passive one.
• Software: Run a VSWR check using ProAIS2 to verify antenna health.

Being seen is the first rule of collision avoidance. Don’t let a $20 piece of cheap cable turn your safety system into a paperweight.