Set up a boat speed display before you leave
- Secure the phone where the display is readable and the sky is unobstructed. Set it up while stationary.
- Open ClearSpeed and allow location access. In iOS Settings, enable Precise Location for ClearSpeed GPS.
- Choose KT for knots. The trip distance changes to nautical miles, rather than road miles or kilometres.
- Wait for the GPS status before reading the speed. Keep the app open on screen; it does not track with the screen locked.
- If you want trip totals, start a trip before setting off and end it when you arrive to keep a private summary.
A GPS-equipped iPhone or Wi-Fi + Cellular iPad is required for satellite speed. A Wi-Fi-only iPad is not a substitute, even if it has internet access through a hotspot.
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.
| Knots | MPH | KM/H |
|---|---|---|
| 5 | 5.75 | 9.26 |
| 10 | 11.51 | 18.52 |
| 20 | 23.02 | 37.04 |
One knot is one nautical mile per hour, exactly 1.852 km/h. For example, a boat moving at 10 knots through the water against a 2-knot current could make about 8 knots over ground. ClearSpeed displays the GPS estimate of the latter; it does not measure current or water speed.
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 with reported location accuracy, so you can see when the signal is weak
- 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.
Will it work without a SIM or mobile data?
ClearSpeed does not need mobile data to display GPS speed. The device still needs a usable satellite fix and location permission. Offline is different from no GPS signal: a tunnel, cabin roof, or obstructed sky can make the reading unavailable. See the Weak GPS checklist.
What is saved from a boat trip?
Ending a trip saves its date and time, duration, distance, average and maximum speed on the device. It does not save a route map, nautical chart, or exportable track. Read how private trip history works.
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 $4.99 once in the U.S. App Store, with no subscription, in-app purchases, or ads. View ClearSpeed GPS on the App Store.