Propeller slip is a crucial concept in marine engineering and aeronautics, referring to the difference between the theoretical distance a propeller would advance in one revolution and its actual distance traveled. It's essentially the 'slippage' of the propeller through the fluid (water or air).
Understanding propeller slip helps in optimizing propeller design and engine performance. A higher slip percentage might indicate an inefficient propeller for the current conditions, or that the engine is struggling to provide enough power. Conversely, very low slip could mean the propeller is too small or the gearing is too low, failing to utilize the engine's full potential.
Actual Speed is the measured speed of the vessel or aircraft through the fluid.
Theoretical Speed is the pitch of the propeller multiplied by its rotational speed (RPM).
function calculatePropellerSlip() {
var pitch = parseFloat(document.getElementById("propellerPitch").value);
var rpm = parseFloat(document.getElementById("rpm").value);
var actualSpeed = parseFloat(document.getElementById("actualSpeed").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = "";
if (isNaN(pitch) || isNaN(rpm) || isNaN(actualSpeed) || pitch <= 0 || rpm <= 0 || actualSpeed < 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for pitch and RPM, and a non-negative number for actual speed.";
return;
}
// Assuming pitch is in meters and speed is in meters per second for direct calculation
// If units differ (e.g., pitch in feet, speed in knots), conversion would be needed here.
// For this example, we'll assume consistent units or that the user knows to provide them.
// Calculate theoretical speed in distance per minute
// Theoretical Speed (distance/minute) = Pitch * RPM
var theoreticalSpeedPerMinute = pitch * rpm;
// Convert actual speed to meters per minute if it was in meters per second
// If actualSpeed is in knots, further conversion to m/min is needed.
// For simplicity, let's assume the user inputs actual speed in the same unit per minute as the theoretical speed will be calculated.
// If actualSpeed is in m/s, multiply by 60.
// If actualSpeed is in knots, convert knots to m/s (1 knot = 0.514444 m/s) then multiply by 60.
// Let's standardize to meters per minute for theoretical speed.
// If the user enters actual speed in m/s, we convert it to m/min.
// If they enter knots, they should be aware of the conversion for input.
// For now, let's assume they input m/min if theoretical is m/min or they understand the unit context.
// A more robust calculator would include unit selection.
// Example: If pitch is in meters, rpm is rpm, actual speed is in m/s.
// Then theoretical speed (m/min) = pitch (m) * rpm (rev/min)
// actual speed (m/min) = actual speed (m/s) * 60 (s/min)
var actualSpeedPerMinute;
// We need to know the unit of actualSpeed. Let's assume it's m/s and convert.
// If the user inputs 'knots', they should ideally know to convert it to m/s first, or we add unit handling.
// For simplicity, let's assume m/s and convert to m/min.
actualSpeedPerMinute = actualSpeed * 60; // Convert m/s to m/min
// Theoretical distance advanced per revolution = pitch
// Theoretical distance advanced per minute = pitch * RPM
// Actual distance advanced per minute = Actual Speed (converted to m/min)
// Calculate slip
var theoreticalSpeed;
// Here theoretical speed is distance covered in one revolution
// If pitch is 2.5 meters, and RPM is 1500, then theoretical speed per minute is 2.5 * 1500 = 3750 meters/minute.
// If actual speed is 5 m/s, then actual speed per minute is 5 * 60 = 300 meters/minute.
// The formula uses speed, not distance per minute.
// Theoretical Speed = Pitch * RPM (This isn't speed directly, but distance per minute, assuming pitch is distance per revolution)
// Let's re-evaluate the formula: Slip = 1 – (Actual Speed / Theoretical Speed)
// Where Theoretical Speed = Pitch * Rotational Speed (in consistent units)
// Let's ensure units are consistent.
// If Pitch is in meters, and RPM is in revolutions per minute:
// Theoretical speed (meters per minute) = Pitch (meters/revolution) * RPM (revolutions/minute)
// If Actual Speed is in meters per second, we convert it to meters per minute:
// Actual speed (meters per minute) = Actual Speed (meters/second) * 60 (seconds/minute)
var theoreticalSpeedMetersPerMinute = pitch * rpm;
var actualSpeedMetersPerMinute = actualSpeed * 60; // Assuming actualSpeed input is in m/s
if (theoreticalSpeedMetersPerMinute 100) slipPercentage = 100;
if (slipPercentage < -100) slipPercentage = -100; // For cases where actual speed exceeds theoretical
resultDiv.innerHTML = "
Result:
";
resultDiv.innerHTML += "Theoretical Speed (per minute): " + theoreticalSpeedMetersPerMinute.toFixed(2) + " m/min";
resultDiv.innerHTML += "Actual Speed (per minute): " + actualSpeedMetersPerMinute.toFixed(2) + " m/min";
resultDiv.innerHTML += "Propeller Slip: " + slipPercentage.toFixed(2) + "%";
if (slipPercentage > 20) {
resultDiv.innerHTML += "Note: A slip percentage above 20% may indicate inefficiency. Consider propeller adjustments or engine tuning.";
} else if (slipPercentage < 0) {
resultDiv.innerHTML += "Note: A negative slip percentage indicates the propeller is advancing further than its pitch suggests, which might point to unusual hydrodynamic conditions or inaccurate measurements.";
}
}