Rate of Turn Calculator Ship

Rate of Turn (ROT) Calculator

Calculation Result:

0 °/min

function calculateROT() { var speed = parseFloat(document.getElementById("shipSpeed").value); var radius = parseFloat(document.getElementById("turnRadius").value); var resultDiv = document.getElementById("resultDisplay"); var rotOutput = document.getElementById("rotResult"); var adviceOutput = document.getElementById("rotAdvice"); if (isNaN(speed) || isNaN(radius) || speed <= 0 || radius 30) { adviceOutput.innerText = "Warning: High Rate of Turn. Ensure cargo is secured and stability is verified."; } else if (rot < 5) { adviceOutput.innerText = "Notice: Slow Rate of Turn. Ensure sufficient sea room is available."; } else { adviceOutput.innerText = "Normal maneuvering rate for standard navigation."; } }

Understanding Rate of Turn (ROT) in Maritime Navigation

In maritime navigation, the Rate of Turn (ROT) is the number of degrees a ship rotates around its vertical axis per unit of time, typically expressed in degrees per minute (°/min). Mastering ROT is essential for safe passage planning, especially in restricted waters, channels, and during pilotage operations.

The Mathematical Formula

Professional mariners use a standard rule of thumb to determine the required ROT for a specific radius at a given speed:

ROT (°/min) = (Speed in Knots × 0.96) / Radius in NM

This formula allows OOWs (Officers of the Watch) to calculate the necessary constant radius turn, which is safer and more predictable than simply applying a fixed rudder angle.

Why ROT Matters for Ship Handling

• Predictability: Using a constant ROT ensures the ship follows a specific circular path on the chart, making it easier to monitor cross-track error.
• Safety: High rates of turn can cause significant heel in vessels with high centers of gravity or cause cargo shifting.
• Wheel Over Point (WOP): Calculating ROT is the first step in determining the Wheel Over Point, which accounts for the time lag between ordering the helm and the ship beginning its swing.
• Pilotage: Pilots often request specific ROTs to stay within narrow dredged channels.

Practical Example

Imagine a container ship approaching a 90-degree turn in a channel. The pilot wants a turn radius of 1.0 Nautical Mile to stay in deep water. The ship is steaming at 10 knots.

Calculation:
ROT = (10 knots × 0.96) / 1.0 NM
ROT = 9.6°/min

By maintaining approximately 10 degrees per minute on the ROT indicator, the navigator ensures the vessel stays perfectly on the planned arc.

Key Factors Affecting ROT

While the calculator provides the theoretical ROT, real-world factors can influence actual performance:

Factor	Impact
Draft/Trim	A trim by the head usually makes the vessel more "pivot-happy" but less stable on course.
Squat/Shallow Water	In shallow water, the turn radius increases significantly due to restricted water flow around the hull.
Current	The ROT formula uses Speed Over Ground (SOG). A following current increases the required ROT for the same radius.