The essentials in 30 seconds
- VHF range is a matter of horizon, thus antenna height. The VHF wave propagates in a near line-of-sight: the radio horizon rule gives approximately 2.2 × √height (m) nautical miles on each side of the link.
- Masthead = the sailboat standard. A whip antenna at 15-17 m dominates the boat's environment and transmits far; it is the default choice whenever a mast is present.
- Stern rail = emergency or mastless boat. At 2 m above water, the local horizon is short and swell obstructs the antenna: practical range drops sharply — usable in coastal waters, insufficient offshore.
- The coaxial cable makes or breaks the installation. On an 18 m mast, an RG58 dissipates over half of the transmitted power; an RG213 about a third. The cable is chosen with the antenna, not afterwards.
- Connectivity is the #1 cause of VHF failures seen in the workshop: a wet connection at the mast base is enough. Systematic waterproofing (self-amalgamating tape + protection).
Table of Contents
The antenna is what transforms your VHF radio into a useful safety tool. An excellent VHF with a poorly installed antenna will see its range collapse; an entry-level radio with a good antenna will achieve its nominal range. The difference is not in the unit, it is in the antenna, the cable, and the connectors. For the choice of the radio itself, see Fixed vs portable VHF + Class B AIS.
VHF physics: why height matters
Marine VHF transmits around 156-162 MHz: the wave propagates in a near line-of-sight, without bending around the Earth's curvature. The range of a link therefore depends on the radio horizon of each antenna. The standard rule (radio horizon, heights in meters):
range ≈ 2.2 × (√h_transmitter + √h_receiver) nautical miles
- Sailboat (masthead antenna, ~17 m) to cargo ship (antenna ~35 m): 2.2 × (4.1 + 5.9) ≈ 22 NM.
- Sailboat (17 m) to semaphore station (antenna ~80 m): 2.2 × (4.1 + 8.9) ≈ 29 NM.
- Stern rail antenna (~2 m) to the same semaphore station: ≈ 23 NM theoretically… but in practice, swell obstructs the antenna, and the deck environment (sprayhood, rigging, crew) absorbs and reflects: the effective range drops far below theory.
The challenge is not the theoretical maximum range, but the practical range in real conditions: the higher the antenna, the cleaner the wave exits the boat's environment — and the more the connection withstands rough seas, precisely when it is needed.
Masthead antenna
The masthead antenna is the sailboat standard: a whip of approximately 1 m, omnidirectional, fixed at the top — ideally clear of the wind transducer and sensors. Our active catalog reference: the Navico 1720 VHF antenna (1.1 m stainless steel whip), with its dedicated 30 m mast cable.
- Connection: coaxial connector at the base, quality cable in the mast (next section).
- Waterproofing: gasket at the antenna base + connector protection (self-amalgamating tape).
- Fastening: stainless steel hardware, checked during each masthead inspection.
Stern rail or backstay antenna: use and limits
A low antenna (stern rail, backstay, emergency mast) has three legitimate uses:
- Emergency — in case of dismasting or main antenna failure. For offshore programs, wiring a two-position coaxial switch to an emergency antenna is a true safety measure.
- Mastless boat — motorboat, RIB, dinghy: the stern rail antenna is then the primary one, accepting its reduced range.
- Dedicated AIS if the installation has a separate receiver/transponder with its own antenna (splitter otherwise).
For primary use on a masted sailboat, a low antenna wastes available height: it is an emergency choice, not a primary installation.
The coaxial cable
The signal attenuates in the cable, and attenuation impacts range. Orders of magnitude at marine VHF frequencies (manufacturer datasheets, to be verified for the exact reference):
- RG58 (~6 mm): on an 18 m mast, over half of the transmitted power is dissipated in the cable. To be reserved for very short connections.
- RG213 / RG214 (~10 mm): over the same length, the loss drops to about a third. This is the standard for a masthead installation — we have the RG214/U and the Ultraflex 7 in the catalog.
- Low-loss cables type LMR-400/Belden 9913: another step down in attenuation — relevant for racing or very tall masts.
Workshop rule: the cost difference between a mediocre cable and a good cable is negligible on the scale of an installation — the range difference, however, can never be compensated for. The cable is chosen at the same time as the antenna.
Waterproof connectors
Two standards are encountered: the PL259 (UHF), classic for leisure VHF, and the N-type, inherently more waterproof, common in professional use. In both cases, it is the connections that determine reliability:
- Mast base — the connection most exposed to water: systematic protection (self-amalgamating tape, sleeve).
- Masthead — gasket under the antenna, greased stainless steel hardware.
- Rear of the unit — tightness to be checked annually.
This is the #1 cause of VHF failures we see in the workshop: a wet connection leads to intermittent failures that are very difficult to diagnose.
Configuration table
| Configuration | Typical Height | Range | For Whom |
|---|---|---|---|
| Masthead + low-loss cable | 15-17 m | The benchmark — maximum horizon, margin in real conditions | Any masted sailboat, offshore priority |
| Masthead + RG58 | 15-17 m | Identical horizon but power curtailed by the cable | To be corrected: the cable negates part of the height benefit |
| Backstay / emergency mast | 10-14 m | Intermediate | Offshore emergency antenna (with switch) |
| Stern rail | ~2 m | Severely reduced in practice (swell obstruction) | Mastless boat, coastal emergency |
The 5 installation errors
- RG58 cable in the mast. The saving is negligible, the loss of range permanent.
- No self-amalgamating tape protection at the mast base. Water infiltrates, the connection degrades: intermittent failures.
- Antenna amidst masthead equipment. Wind transducer, sensors, lights: the antenna must be clear of the rest, otherwise radiation suffers.
- Coaxial cable routed alongside power cables (windlass in particular): interference in the radio. Separate, cross at 90° if necessary.
- No SWR check after installation. The standing wave ratio verifies the entire antenna + cable + connectors; a high SWR indicates a fault and stresses the transmitter. Systematic check at the end of installation in the workshop.
Three workshop cases
Case 1 — Sun Fast 3300, club racing
1 m whip antenna at masthead + low-loss cable throughout its height + self-amalgamating protected connectors, installed during the 2024 re-stepping. SWR measured at the end of installation: 1.3:1 on channel 16 — compliant. Observed range to local semaphore station: 18 NM in real conditions.
Case 2 — Mini 6.50, double racing antenna
Redundancy required by the program: main masthead antenna + emergency antenna on backstay, two-position coaxial switch at the panel. No radio failures on the Mini Transat 2025.
Case 3 — 8 m mastless sailboat (dinghy sloop)
2 m whip antenna on stern rail + short coaxial connection. Observed practical range of 7 to 9 NM to local ferries — known and accepted limit for summer coastal use.
Annual maintenance
- Visual inspection: intact whip, waterproof base gasket, tightened hardware.
- SWR check each season; if it degrades, inspect the connector before blaming the antenna.
- Connector protection to be redone periodically — the saline environment eventually degrades everything.
- Real radio test before each major navigation: check call, clarity confirmation.
FAQ
1 m whip antenna or long antenna on a sailboat?
The approximately 1 m whip (gain around 3 dB) is the sailboat standard: its more « round » radiation pattern tolerates heeling. Longer antennas with higher gain concentrate energy horizontally — an advantage on a boat that stays flat, a disadvantage on a heeled sailboat.
How long does a VHF antenna last?
A good ten years in leisure use. The weak point is not the whip but the waterproofing of the base and the connectors — hence the annual inspection.
Is a separate antenna needed for AIS?
AIS transmits on dedicated VHF channels (161.975 / 162.025 MHz): a combined VHF with integrated AIS (like the B&G V60-B pack) uses a single masthead antenna. A separate AIS transponder, however, needs its own antenna or a splitter — this is a matter of architecture, not channels.
Is a lightning arrester necessary?
For offshore programs or in stormy areas, it is a relevant protection, to be installed as close to the antenna as possible. In temperate coastal areas, it is a trade-off — let's discuss it at the time of installation rather than applying an absolute rule.
Can you measure SWR yourself?
Yes, with a VHF SWR meter inserted between the unit and the antenna: brief transmission, reading. An SWR close to 1:1 is excellent; beyond 2:1, look for the fault (connector first). We systematically measure it at the end of installation.
Also read
- Fixed vs portable VHF + Class B AIS — the safety combination
- EPIRB vs PLB vs AIS MOB — choosing your distress beacon
- NMEA 2000: architecture and cabling
- VHF/AIS antennas catalog · Cabling
About the author
Pol Conin, Digital Manager at Skysat. A software engineer and tech entrepreneur, Pol joined the adventure to bring Skysat into the digital age. See his author page for the complete list of signed articles.
Transparency: Skysat distributes the cited antennas and cables and installs them in its workshop in Carnac; the claimed experience is based on VHF installations carried out since 2018. This changes neither the physics nor the cases where a stern rail antenna is the correct solution.
