A marine radar for a mid-size cruising sailboat should be chosen on three things: dome vs open-array to fit your mast, arch, or pole; a working range (typically 3–24 nautical miles) that matches how you actually cruise; and integration with the chartplotter network you already run. For most 30–45 ft boats, an 18–24″ dome radar covers fog, night arrivals, and weather avoidance without adding meaningful weight or windage aloft.
On a mid-size cruiser, radar is the one sensor that keeps working when eyes and AIS do not — in fog, heavy rain, or a moonless night approach, radar shows you ships, squalls, and the coastline your eyes cannot. Get the type and size wrong and you either overpay for offshore-grade gear you never need, or you undersize a unit and lose resolution exactly when you need it most. This guide walks through dome vs open array, range and beamwidth, mounting, and how to wire it into the electronics you already run.
Marine radar at a glance
Representative, currently available radar units spanning compact dome radars through open-array antennas. Use them as reference points for the type and range you need.
| Radar (SKU) | Type | Size | Price |
|---|---|---|---|
| Garmin GMR 18 HD3 (GAR-010-02843-00) | Pulse dome | 18″ dome | $1,799.99 |
| Garmin GMR Fantom 18x (GAR-010-02584-10) | Solid-state Doppler dome | 18″ dome | $2,299.99 |
| Simrad HALO20+ (SIM-000-14536-001) | Pulse compression dome | 20″ dome | $2,499.00 |
| Raymarine Quantum 2 / Q24D (RAY-T70549) | CHIRP Doppler dome | 18″ dome | $2,759.99 |
| Garmin GMR 2534 xHD3 (GAR-K10-00012-28) | Open array, 25kW | 4′ array | $8,899.99 |
| Simrad HALO 3004 (SIM-000-15763-001) | Open array, pulse compression | 4′ array | $8,924.00 |
What is the difference between a dome and an open-array radar?
A dome radar is a sealed, self-contained radome that houses the antenna and transceiver in one compact unit — it mounts on a pole, arch, or radar mast bracket and needs no separate pedestal. An open-array radar uses a longer, unenclosed rotating antenna (typically 3–6 ft) driven by a separate pedestal, giving a narrower beamwidth and sharper target separation at range, at the cost of size, weight, and windage. For a sailboat under 45 ft, a dome is almost always the right call: units like the Garmin GMR 18 HD3 (GAR-010-02843-00) and Simrad HALO20+ (SIM-000-14536-001) deliver strong coastal performance without the weight aloft that an open array demands. Open arrays such as the Garmin GMR 2534 xHD3 (GAR-K10-00012-28) or Simrad HALO 3004 (SIM-000-15763-001) earn their keep on larger cruisers, commercial-traffic-heavy routes, or offshore passages where long-range target discrimination matters more than windage.
How do you size a radar dome for your sailboat?
Size follows how you actually cruise, not the biggest number on the spec sheet. An 18″ dome such as the Garmin GMR 18 HD3 covers typical coastal ranges out to several nautical miles and is light enough to mount on most radar arches and mast brackets. Step up to a 20″ unit like the Simrad HALO20+ for slightly longer range and a narrower beam, which sharpens separation between two boats close together. If you regularly run offshore passages, want bird- and weather-cell detection, or need to hand off targets automatically to your autopilot, a solid-state Doppler dome — the Garmin GMR Fantom 18x (GAR-010-02584-10) or the Raymarine Quantum 2 / Q24D (RAY-T70549) — adds target motion (approaching vs. receding) directly on the display, which is a meaningful safety upgrade in a crossing situation.
Why does Doppler or pulse-compression technology matter?
Traditional pulse radar sends a short burst of energy and times the echo — simple and proven, but it can struggle to separate a small target from sea clutter close in. Pulse-compression radars (Simrad HALO, SI-TEX NavPro) transmit a longer, coded pulse that the receiver decodes for both long range and fine resolution at once. Solid-state Doppler radars (Garmin Fantom, Raymarine Quantum 2) go further: they measure the frequency shift of the return to tell you whether a target is closing or opening, and typically color that motion on-screen. For a cruising sailboat crossing shipping lanes or working an anchorage in fog, that extra second of clarity on which vessel is actually approaching is the entire point of upgrading past a basic pulse dome.
How do you mount a radar on a sailboat mast, arch, or pole?
Dome radars mount three ways on a cruising sailboat: a dedicated radar pole or post aft of the cockpit, a stern arch or davit structure that already carries solar and antennas, or a mast bracket partway up the mast for maximum range from height (every foot of mounting height adds meaningfully to radar horizon distance). Keep the dome level, clear of the mainsail’s swept area, and at least a few feet from magnetic compasses. Run the supplied power/data cable (radars typically ship with a fixed cable length, such as the 10m cable on the Raymarine Quantum 2) to your chartplotter or network switch, and confirm cable length reaches your intended mount point before you drill.
How does radar integrate with your chartplotter and autopilot?
Modern dome radars connect over the same NMEA 2000 or proprietary Ethernet backbone as your chartplotter, so the radar image overlays directly on the chart rather than living on a separate screen. Doppler units add functions like MARPA-style target tracking and collision alarms that work with your autopilot and AIS to flag a closing vessel automatically. Before buying, confirm brand compatibility — a Garmin dome pairs with Garmin MFDs, a Simrad or B&G dome with Simrad/B&G displays, and Raymarine domes with Raymarine’s LightHouse network — cross-brand radar-to-MFD pairing is the exception, not the rule.
Which radar should you choose?
- Coastal weekender, budget-conscious: an 18″ pulse dome such as the Garmin GMR 18 HD3 covers fog and night arrivals without breaking the electronics budget.
- Regular coastal cruiser crossing traffic lanes: step up to a Doppler dome (Garmin Fantom 18x or Raymarine Quantum 2) for target motion and CHIRP performance.
- Longer-range or offshore cruiser: a 20″ pulse-compression dome (Simrad HALO20+) balances range and low windage for passages beyond day-sailing distance.
- Larger cruiser or commercial-adjacent routes: an open array (Garmin GMR 2534 xHD3, Simrad HALO 3004) trades size and weight for the sharpest target separation at long range.
Whichever size you choose, match the radar brand to your existing (or planned) chartplotter network so the image lands on the same display you already trust.
Frequently asked questions
Do I need radar if I already have AIS?
Yes — AIS only shows vessels transmitting an AIS signal. Radar shows everything with a physical return: unlit small craft, squalls, land, and buoys, which is why cruisers run both together rather than one or the other.
What size dome radar is right for a 30–45 ft sailboat?
An 18–20″ dome, such as the Garmin GMR 18 HD3 or Simrad HALO20+, is the common range for this size boat — enough range and resolution for coastal cruising without excess weight aloft.
What is the advantage of a Doppler radar over a standard pulse radar?
A Doppler radar (Garmin Fantom, Raymarine Quantum 2) reads whether a target is approaching or moving away and typically displays that as a color on screen, giving you an immediate read on collision risk that a standard pulse radar cannot show directly.
Can I mix radar brands with my existing chartplotter?
Generally no — radar domes are built to pair with their own brand’s network (Garmin with Garmin, Simrad/B&G with Simrad/B&G, Raymarine with Raymarine). Confirm compatibility with your specific MFD model before ordering.
Where should a radar dome be mounted on a sailboat?
On a radar pole aft of the cockpit, a stern arch, or a mast bracket — kept level, clear of the mainsail’s sweep, and mounted as high as practical, since mounting height extends the radar horizon.
Shop marine radar
Browse dome and open-array radars chosen for cruising sailboats, from compact 18″ domes to long-range open arrays.
Garmin GMR 18 HD3 18″ Radar Dome