Selecting the correct propeller for your boat is crucial for optimal performance, fuel efficiency, and engine longevity. A propeller's job is to translate the rotational power of your engine into thrust that pushes your boat through the water. Quicksilver, a well-known marine parts manufacturer, offers a wide range of propellers designed for various boat types and engine configurations.
Key Factors in Propeller Selection:
Engine Horsepower (HP): This is the fundamental measure of your engine's power output. It dictates the general size and pitch of propeller that can be effectively driven.
Gear Ratio: This ratio, found in your boat's lower unit, indicates how many times the engine crankshaft turns for each full revolution of the propeller shaft. A higher gear ratio (e.g., 2.33:1) means the propeller spins slower relative to the engine, often allowing for a larger diameter propeller.
Boat Weight: A heavier boat requires more thrust to get on plane and maintain speed. Heavier boats generally benefit from propellers with larger diameters and/or more blades to generate this increased thrust.
Hull Type: Different hull designs have varying hydrodynamic properties.
Planing Hulls: These hulls are designed to lift out of the water and skim across the surface at higher speeds. They typically require propellers that offer good top-end speed and efficiency.
Displacement Hulls: These hulls push through the water and are generally found on slower, heavier vessels. They prioritize torque and low-end thrust for pushing the hull.
Desired Speed: Your intended cruising speed or top speed will influence the pitch and diameter of the propeller. A higher desired speed might necessitate a higher pitch.
How the Calculator Works:
This calculator provides an estimated propeller size based on the input parameters. It uses general formulas to approximate the relationship between your boat's characteristics and the propeller needed.
Diameter: This is the distance across the circle swept by the propeller blades. A larger diameter generally provides more thrust at lower speeds.
Pitch: This is the theoretical distance the propeller would move forward in one full revolution. A higher pitch means the propeller "bites" more water per revolution, leading to higher speeds but requiring more power.
Disclaimer: This calculator is a guide only. Actual propeller performance can vary significantly based on specific hull design, engine condition, load, and water conditions. It is always recommended to consult with a marine professional or refer to your engine manufacturer's guidelines for the most accurate propeller selection.
function calculatePropellerSize() {
var hp = parseFloat(document.getElementById("engineHorsepower").value);
var gearRatioStr = document.getElementById("gearRatio").value;
var boatWeight = parseFloat(document.getElementById("boatWeight").value);
var hullType = document.getElementById("hullType").value;
var desiredSpeed = parseFloat(document.getElementById("desiredSpeed").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
if (isNaN(hp) || isNaN(boatWeight) || isNaN(desiredSpeed) || gearRatioStr === "") {
resultDiv.innerHTML = "Please enter valid numbers for all fields.";
return;
}
var gearRatio;
if (gearRatioStr.includes(':')) {
var parts = gearRatioStr.split(':');
if (parts.length === 2) {
gearRatio = parseFloat(parts[0]) / parseFloat(parts[1]);
} else {
resultDiv.innerHTML = "Invalid gear ratio format. Use 'X.XX:1' or 'X.XX'.";
return;
}
} else {
gearRatio = parseFloat(gearRatioStr);
}
if (isNaN(gearRatio) || gearRatio <= 0) {
resultDiv.innerHTML = "Please enter a valid gear ratio.";
return;
}
var estimatedDiameter = 0;
var estimatedPitch = 0;
// Basic estimation formulas – these are highly simplified and for illustrative purposes.
// Real-world propeller selection involves more complex calculations and empirical data.
// Diameter estimation (rough guide)
if (hullType === "planing") {
estimatedDiameter = (hp * 0.1) + (boatWeight * 0.005) + (desiredSpeed * 0.1);
} else { // displacement
estimatedDiameter = (hp * 0.15) + (boatWeight * 0.008) + (desiredSpeed * 0.05);
}
// Pitch estimation (rough guide)
if (hullType === "planing") {
estimatedPitch = (desiredSpeed * 1.5) + (hp * 0.5 / gearRatio);
} else { // displacement
estimatedPitch = (desiredSpeed * 1.0) + (hp * 0.8 / gearRatio);
}
// Clamp values to reasonable ranges (example ranges)
estimatedDiameter = Math.max(8, Math.min(estimatedDiameter, 20)); // Example: 8 to 20 inches
estimatedPitch = Math.max(6, Math.min(estimatedPitch, 25)); // Example: 6 to 25 inches
resultDiv.innerHTML =
"