An inclinometer, also known as a heel or clinometer, is a crucial instrument in maritime navigation used to measure a vessel's heel, or the side-to-side tilt. This tilt occurs when the ship is influenced by wind, waves, or uneven weight distribution on board. The inclinometer provides real-time data on this tilt, which is vital for maintaining the ship's stability and safety.

Traditional inclinometers use a pendulum or ball to indicate the angle of tilt on a graduated scale, while modern electronic models utilize sensors to measure the angle more precisely, often displaying the data digitally. Monitoring the heel is especially important on sailboats and yachts, where excessive tilt can lead to instability or even capsizing. By keeping a close eye on the inclinometer, the crew can take corrective actions, such as adjusting the sails, altering the course, or redistributing weight.

In large vessels, such as cargo ships, inclinometers play a vital role in ensuring that the ship remains balanced, particularly when loading or facing strong winds. Regular calibration and proper installation of the inclinometer are essential to guarantee accurate readings and effective use.