Imagine you just pulled your boat out of the water and found the propeller seriously corroded or damaged. Increasing the pitch will decrease engine rpms and decreasing the pitch will increase engine rpms. Inboard Sizing: Choosing the right propeller for your boat requires several pieces of information to allow us to give you the best suggested propeller size for your boat and engine combination. based on a 25°C day (77°F) day is output. Slip is not a measure of propeller efficiency. Mercury Precision Parts. gauge. A boat propeller has two basic dimensions: diameter and pitch. Parts & Accessories. Mach number. Smaller prop diameters generally go with smaller engines, or with fast high performing boats. So that translates into a 16-pitch prop of the same style and manufacture. Is it important to know your prop’s slip? Start by clicking on the type of boat hull that most closely matches your boat. All Rights Reserved. Due to prop slip the boat is actually going slower than the theoretical speed. Accuracy: Best. propeller is turning. For example, a propeller described as 14.5 x 19 has a diameter of 14.5 inches and a pitch of 19 inches. This propeller rpm times the prop pitch determines the theoretical distance that the boat should have moved in one minute, which can be converted to a theoretical boat speed in miles per hour. The calculator will automatically compute the 5 th variable. This calculator is designed to give any missing value from the 5 … The "angle of attack" is measured from the pitch gauge reference. We’ll continue to use this conceptual aircraft, specify an engine and propeller, and then use this information to estimate the variation in thrust produced with speed. most cases this is different from the conventional airfoil datum. The calculations and results are based on imperical data and formulas. FAQs. increase in the velocity of the air in front of the propeller disc that The higher the pitch number, the more bite the prop takes out of the air. US units of inches (in) and miles per hour (mph). The results are only as acurate as the data you enter. The pitch is the distance a propeller moves and the amount of power needed to turn the propeller. This has the effect of increasing the effective Engine rpms and pitch are inversely related. These dimensions are often stamped or cast right on the propeller. To account for this the input airspeed must be higher than the The results are only as acurate as the data you enter. Elevation: M… Therefore any results in the calculated engine power field should be monitored carefully! Of course, most boaters will want something that is in between – good hole shot with acceptable top end speed. Conversely, a two-inch decrease in pitch will result in an increase of 300 to 400 rpm. If you prop your boat to maximize top speed, acceleration will be compromised and visa-versa. Only if you care about insignificant, little items like thrust. The calculations do not include the effect of inflow. Inboard Prop Sizing: Allow the experts at Propeller Depot to complete your free inboard propeller sizing. Propeller Shop. Decrease your current pitch prop (19) by 17% and you get a 15.80 pitch prop to achieve 6000 rpms. As the propeller (with high-pitch) rotates faster and faster it is stalling more and more. The propeller pitch, or prop pitch, depends on the diameter and the pitch of the boat or airplane. To use our boat prop calculator, you need four inputs: All marine propellers involve a tradeoff. Calculate; Engine RPM. The second number, pitch, is the length of the prop’s twist section. timed airspeed. Enter Boat Weight, People & Gear and Fuel Capacity. The propeller revolution rate is the engine rpm divided by the gear ratio. Conversely, to increase top speed, consider increasing your pitch. Going back to the question of performance at WOT, if your engine is under revving, consider a propeller with less pitch. Copyright © 2020 BoaterInput. You can change one parameter and recalculate the rest. Therefore, the first consideration is whether to optimize top speed,  acceleration or some combination of the two. Enter RPM, Top Speed and Propeller Pitch for the most accurate results. GoBrushless Propeller Thrust Calculator (you will need to select the propeller brand, size and pitch and enter the thrust ounces; leave the altitude at the default of 800) Once you have the RPM, refer to the above formula to determine the propeller pitch speed. If it is the former, then it might not make much difference after you account for the fact that each 1″ increase in pitch will result in approximately a 200 decrease in RPMs. can be felt by holding a hand in front of the propeller while the Essentially, slip is no more than the difference between a propeller’s theoretical pitch and its real-world, in-the-water progression. The angle of attack has been adjusted near the tip for the effect of Knowing the theoretical speed for your boat can help you select the proper pitch. In Note the angle between the edge of the propeller hub and the base of the protractor. Length. These dimensions are used to describe the propeller, usually in inches, and always stated as diameter x pitch. Accuracy: Better. Boat Prop Calculator to Help Select the Right Pitch. The lower the prop pitch, the better your hole-shot. Pitch Calculator. View All Propellers. Mercury® Parts Catalog. If it is the later, then you likely have room to improve your top speed. Prop Guide:Use our revoluntionary boat propeller guide to find the perfect boat prop for your outboard, stern drive, or ski/wake marine engine. The calculated propeller sizes are based on standard propeller designs; 2 blade = 30% blade area ratio 3 blade = 50% blade area ratio 4 blade = 69% blade area ratio Weight. To see the potential impact on top speed, enter your current values for Max RPMs, Gear Ratio, If you have a different way of measuring Boat Propeller Calculator You can use this boat propeller calculator to determine one of five variables: boat speed, propeller slip, propeller pitch, engine gear ratio, or engine revs. Important remarks: The propeller's pitch has a significant effect on the required engine power! So, the 200 RPM rule just does not add up, subtracting 5” of pitch from a 19 down to a 14. Propeller Guide: Utilize our best in class boat propeller guide to find the correct propeller for your Outboard, Ski/Wake, or Stern Drive marine engine. Propeller Terms - “Prop Talk” Propeller size is expressed with two numbers, diameter and pitch, with diameter always stated first. kilometers per hour (kph). Propeller Pitch. Pitch Speed is the Mean Geometric Pitch times RPM, which means the speed the aircraft would make if there was no slip. However, this comes at a price: top speed. Search by serial number to find the exact part you need. Otherwise circular Tip Speed is shown. Links. Calculate; Actual Speed (MPH) Calculate; Propeller Slip. Calculate; Choosing a Prop. per square ft of the prop disc. Determine the correct diameter and pitch of a propeller for any given vessel and engine. This is especially relevant if you ARE hitting the max RPM level established by the engine manufacturer with your current prop. station increment are taken from a Prather pitch This calculator is free to use as often as you wish. Mercury Precision Parts and Mercury Lubricants keep your engine running at peak performance. Pitch Speed Calculator Input a propeller pitch in inches and its RPM to see the theoretical maximum speed in miles per hour. If your engine is over revving, consider a propeller with more pitch. Be sure to take a look at the Prop Slip page for an explanation of how to find your prop … Use your calculator to determine the tangent of the pitch angle. This is the Prop Calculator. The same is true with a prop. Send a Repair. The default initial station position and Calculate Pitch by: Performance. For very high pitch props (70"-80") the calculated Tip Speed has been adjusted 5%-6% to approximate true helix Tip Speed. Here’s the math, in case you care to calculate slip. The sketch below shows a plan view of the two-seat conceptual Light Sport Aircraft (LSA) that we used in the drag study covered in Part 9to calculate the total drag variation with velocity. This is the increase in the velocity of the air in front of the propeller disc that can be felt by holding a hand in front of the propeller while the propeller is turning. Click the "Register" button or click here to create a free account. a prop, adjust those parameters accordingly. First, you need to ascertain the theoretical speed: (pitch x RPM)/(gear ratio x 1056) = theoretical speed. Nor does it account for propeller inefficiencies. units (they used to be called metric) of millimeters (mm) and Then, decrease the pitch by an inch or two. Marine Propeller Calculator This calculator requires the use of Javascript enabled and capable browsers. Contact Us. The Virtual Pitch Speed is usually 20 to 30% higher than the Pitch Speed. An approximate Mach number for the blade station in question However, it is hard to tell whether your RPM level is the best your engine can do or if it is being capped by the engine’s rev-limiter (to protect the engine). For example, if the pitch angle is 23 degrees, then its tangent is 0.4245. The calculations and results are based on imperical data and formulas. Use this calculator to figure out just about anything in regard to propeller, ratio, RPM and speed. Picking a perfect prop for an individual boat depends on a large number of factors including hull design, weight, altitude, engine, and usage patterns. To increase acceleration, consider reducing your pitch. The lower pitch makes the engine reach maximum rpm at slower speeds. That’s 4 inches in our example. airspeed. It does not account for pitch measurement imprecision or unloading in the air. A rough approximation for F2A is 5 kph addition to the Thus, a higher pitch value typically donates a faster aircraft. This is called the pitch angle. The lower the ratio, the more pulling power from a standstill. Pitch Calculator. Just be sure that whatever size prop you use your engine operates within its recommended RPM range. Download the Pitch Calculator here Compatible operating systems: Please note that the pitch calculator software will only work on the following platforms - Windows XP Windows Vista Unfortunately Windows 7 and Mac OS are not supported. This makes particular sense if you are NOT hitting the max RPM level established by the engine manufacturer when running at Wide Open Throttle (WOT) with your current prop. Diameter is two times the distance from the center of the hub to the tip of any blade. If technical information is unavailable, determine pitch by entering Boat length. This calculator will help guide you to the proper propeller for your boat hull type and boating style. This calculator is free to use as often as you wish. Not a member? To see the potential impact on top speed, enter your current values for Max RPMs, Gear Ratio, Pitch and Prop Slip in the Boat Prop Calculator tool. Recommended pitch is theroetical as it assumes no "slip". The diameter is determined by the revolutions per minute at which the propeller will be turning and the amount of power need to turn the propeller. All of them... Don’t miss a prop. Use the CalcT button to figure the theoretical speed from the actual speed and slip. Inboard Propeller Sizings & Prop Guide for Outboards, Sterndrives, and Ski/Wake engines. This has the effect of increasing the effective airspeed. airspeed. A bigger diameter results in more thrust and noise. As a general rule, a two-inch increase in pitch will result in a reduction of 300 to 400 rpm. Slip is the most misunderstood of all propeller terms, probably because it sounds like something undesirable. Your looking for a replacement and a friend has an old propeller but is not sure of the size. This is colour coded to give an immediate idea of the potential performance of that prop with the selected motor KV and battery voltage. Ideal Tip Speed varies depending on the H.P. Often the pitch angle is not constant along the prop's blade, so it is typically specified at 75% from the center of the blade. This simple pitch measuring app is for educational purposes and is ideal for someone who can't read any numbers on the propeller. To use the calculator, input four of the five variables. Sign in to BoaterInput using the username or email address and password you selected. Prop pitch explained: Think of a propeller as you would a car's axle ratio. The most convenient result to check on the propeller speed calculator is the metres per second (m/s) tip speed. Propeller Pitch Calculator. By superimposing the thrust and drag variation on the same graph we can estimate the theoretical top speed of our aircraft (the speed at which the available thrust i… The calculated propeller sizes are based on standard propeller designs; 2 blade = 30% blade area ratio 3 blade = 50% blade area ratio 4 blade = 69% blade area ratio However, as you do this, you should increase your RPMs by approximately 200 for each 1″ reduction in pitch (until the maximum RPM rating is reached). Calculate; Gear Ratio. Prop Slip Calculator.