Speed over ground
GPS measures how fast you move over the earth — speed over ground (SOG). A paddlewheel log measures speed through the water. With a current running, the two differ; that's expected, not an error.
What you get in knots mode
- Live speed in knots (1 knot = 1.852 km/h ≈ 1.15 mph)
- Trip distance in nautical miles
- Average and maximum speed, elapsed time
- GPS status, so you know when the reading is trustworthy
- Night appearance for low light; landscape layout for a helm mount
Works without cell coverage
The app doesn't need an internet connection to show speed. Offshore, the first GPS fix can take longer without cellular assistance; wait for Good GPS.
Practical tips
- Use a waterproof case and a secure mount. Spray and salt are harder on phones than any app.
- Bright sun reduces screen visibility; the light appearance usually reads better in daylight.
- The app only measures while it is open on screen. Connect power for long runs.
Not a marine instrument
ClearSpeed is not a chartplotter, navigation system, depth sounder, or safety device, and it has no charts, anchor alarm, or MOB function. Carry proper marine equipment and follow local rules, including no-wake and speed zones.
Try it on your next trip
ClearSpeed GPS is $3.99 once in the U.S. App Store, with no subscription, in-app purchases, or ads. View ClearSpeed GPS on the App Store.