Marine Compass Buying Guide: Mount Types, Sizing, Placement and Compensation
Quick answer: Every boat with electronics should still carry a magnetic compass, because it works when GPS, batteries and screens do not. Pick the mount style that fits your helm (flush, surface, bracket, bulkhead or binnacle), choose a dial size you can read from the wheel, and mount it in your line of sight at least two feet from speakers, electronics and steel where possible. Then compensate it so it reads true on your boat.
A good marine compass is the simplest, most reliable navigation tool on board. It needs no power, no satellites and no software updates. When the chartplotter goes dark in a storm or the electrical system fails at night, the compass still points the way home. This guide covers mount types, card styles, sizing, placement and compensation, so the one you buy is accurate when it matters.
Step 1: Choose a mount style
| Mount | How it installs | Best for |
|---|---|---|
| Flush mount | Recessed into a cutout in the dash | Center consoles, cruisers, a clean factory look |
| Surface or dash mount | Sits on top of a flat or sloped dash | Boats with no room for a cutout |
| Bracket mount | On a bracket, can be removed or angled | Small boats, overhead or tilted locations |
| Bulkhead mount | On a vertical surface | Sailboat cockpit bulkheads |
| Binnacle mount | On top of a pedestal at the wheel | Sailboats with wheel steering |
Step 2: Pick a card style
- Flat card: read from above, like a traditional compass. Common on sailboat binnacles.
- Front-reading (direct reading) dial: read straight ahead through a dome. Typical on powerboat dashes.
- Combination (combidial): readable from above and the front.
Choose the style that you can read easily from your normal seated or standing position at the helm.
Step 3: Size the dial
Bigger dials are easier to read and steadier in rough water. Small boats and kayaks use compact compasses around 2 to 3 inches. Most center consoles and runabouts are well served by 3 to 4 inch dials. Larger cruisers and offshore boats benefit from 4 to 5 inch dials that stay readable while the boat is moving. Dark dials with white numbers are easier to read at night with red lighting.
Step 4: Place it right
Placement is the difference between an accurate compass and a decoration.
- Mount it on or parallel to the boat's centerline, with the lubber line pointing straight at the bow.
- Keep it as far as practical from speakers, electronic displays, radios, wiring, and steel objects. Speakers contain strong magnets and are a common cause of large errors.
- Put it in the helmsman's natural line of sight so you can steer by it.
- Run any lighting wires as a twisted pair to cancel their magnetic field.
Steel and aluminum boats need compasses designed for them, with stronger compensation.
Step 5: Compensate and check it
Every boat has some magnetic influence of its own, called deviation. Most marine compasses have built-in compensators, small adjustment screws used to remove as much deviation as possible.
- With engines and electronics running as normal, run known headings (or compare to GPS course on a calm day) and adjust the compensators following the manual.
- Write a deviation card for any remaining error on key headings and keep it at the helm.
- Re-check after adding electronics, speakers or anything metal near the helm.
Step 6: Care for it
Use a cover to protect the dome from UV, which yellows and crazes it over time. A bubble in the fluid usually means a leak and needs service. Check the light bulb or LED before night trips.
Step 7: Use it with your electronics
Note your compass heading against your GPS course on a calm day with no current, and get in the habit of glancing at both. If they disagree by more than a few degrees on a steady course, something has changed near the helm. Also learn the difference between magnetic and true north: charts and GPS can show either, and the local variation is printed on your chart's compass rose. Set your plotter to the same reference your compass uses so the numbers match.
Our picks by boat
All in stock at Boat Supplies Direct. Ritchie has built marine compasses in the U.S. for more than a century.
Small boats and skiffs
Ritchie S-53 Explorer Surface Mount, the B-51 Explorer Bracket Mount, or the V-57.2 Explorer Dash Mount.
Center consoles and runabouts
Ritchie F-82 Voyager Flush Mount or the HF-742 Helmsman Flush Mount for a larger, easier-to-read dial.
Offshore and sportfish
Ritchie SS-1002 SuperSport Flush Mount, built for fast boats, or the FN-201 Navigator for larger helms.
Sailboats
Ritchie BN-202 Navigator Bulkhead Mount or the DNB-200 Navigator Binnacle Mount.
Steel boats and handheld backup
Ritchie HB-845 Steel Boat Compass, and the Ritchie X-11 SportAbout Handheld for the dinghy or ditch bag.
Frequently Asked Questions
Do I need a compass if I have GPS?
Yes, as a backup. A magnetic compass needs no power or satellites, so it keeps working if your electronics or electrical system fail.
Where should a boat compass be mounted?
On or parallel to the centerline in the helmsman's line of sight, as far as practical from speakers, electronics, wiring and metal.
Why is my boat compass wrong?
Usually deviation from nearby magnets or metal, most often speakers, electronics or new gear installed near the helm. Move the source if you can, then compensate the compass.
What size compass do I need?
Small boats use about 2 to 3 inch dials, most runabouts and center consoles 3 to 4 inches, and larger offshore boats 4 to 5 inches.
What is compass compensation?
Adjusting the compass's built-in correctors to cancel the boat's own magnetic influence, then recording any remaining error on a deviation card.
Why does my compass have a bubble?
A bubble usually means the fluid has leaked. Have the compass serviced or refilled by the manufacturer.
This guide is general information. Follow your compass manufacturer's installation and compensation instructions.
