Hull Speed

Hull Speed is a simple speedometer for sailors. It shows your speed over the water in knots — big, clear, and accurate — on your iPhone and Apple Watch, with nothing else to clutter the display. Built for trimming sails: make a small adjustment, then watch the live trend graph to see if the speed changed. FEATURES • Accurate GPS speed in knots, updated every second, using the same Doppler method as dedicated marine instruments — no paddlewheel to foul or calibrate. • A live speed graph on a steady, fixed scale, so a small gain from a trim change is easy to spot. • Enter your boat's waterline length and Hull Speed draws your theoretical hull speed right on the graph — see at a glance how close you are to it. • Apple Watch app with a Keep Awake mode that holds the screen on while you sail. • Completely private — your location is used only to compute speed on your device, and is never stored, sent, or shared. No accounts, no ads, no tracking.