Most propellers will have measurements stamped between the blades, or around the hub on the aft end.
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Let&#;s look at this example:
14-1/2 X 19 RH 3 Blade SS Apollo Propeller
We&#;ll break it down by section:
14-1/2 : The propeller diameter. The diameter is always the first set of numbers.
19: The pitch of the propeller. The pitch is always the second set of numbers.
RH: This is the propeller&#;s rotation. Either RH clockwise or LH counterclockwise.
3 Blade: This is the number of blades. It can be 2, 3, 4, or 5 blades.
SS : This represents the propeller material. AL = Aluminum & SS = Stainless Steel.
An inboard will be either Bronze or Nibral, older inboards may also be Stainless Steel.
Apollo Propeller: This is the style or brand of the propeller. You may see a name, but not always.
The diameter of a propeller is two times the distance from the center of the hub to the tip of the blade. It also can be looked at as the distance across the circle that the propeller would make when rotating. The propeller&#;s diameter is the first number stamped or embossed on the propeller and the first number when describing a propeller&#;s dimensions.
Pitch is the theoretical forward movement of the propeller during one revolution, assuming there is no &#;slippage&#; between the propeller blade and the water. 19 pitch would indicate that your boat should propel 19&#; for every rotation of the shaft. For most boats, there is slippage and therefore the distance advanced is less than the design pitch. The amount of slippage varies from boat to boat. The propeller&#;s pitch is the second number stamped or embossed on the propeller and the second number when describing propellers dimensions.
To measure pitch when the stamps are unreadable, we place outboard propellers and small inboard propellers on our pitchometer. The pitchometer measures the distance from the top edge of the blade to the bottom, giving us an accurate pitch measurement. Most inboard propellers get a digital analysis on our MRI machine, which indicates pitch at three points on each blade, as well as track and blade spacing.
From behind the boat looking forward to the propeller(s), a right-hand propeller rotates clockwise and a left-hand propeller rotates counterclockwise. Many single-engine boats rotate clockwise using a right-handed propeller. Two propellers rotating the same direction on twin-screw boats will create steering torque. In other words, two right-handed propellers pull the stern hard to the right and the bow to the left.
Two counter-rotating (opposite direction) propellers on twin-engine boats eliminate this steering torque because the left-handed propeller balances out the right-hand propeller. This results in better straight-line tracking and helm control at high speed.
Insider trick: when you place your hand against the hub of a propeller, your thumb will point at the hub, indicating the rotation.
Right and Left Hands placed against Right and Left Hand Rotating Propellers
Many of today&#;s propellers incorporate a cup at the trailing edge of the propeller blade. This curved lip on the propeller allows it to get a better bite on the water. This results in reduced ventilation, slipping, and allows for a better hole shot in many cases. A cupped propeller also works well where the motor can be trimmed so that the propeller is near the surface of the water. The cup will typically result in higher top speed without affecting RPM&#;s on one of these applications.
(DOWNLOAD OUR PITCH CHOOSING PDF HERE)
September 14,
The propeller is the part of the boat that is most in contact with the water. As a result, it is the one part of the boat that is most likely to degrade quickly due to the mechanics of the engine or the salinity of the water.
Before considering any change, it is important to know how to measure the propeller of your boat.
With this in mind, the National Boating Safety School&#;s boating specialists explain how to measure a boat&#;s propeller.
The propeller is one of the many parts of a boat. It is designed to propel the boat forward or in reverse. There are times when you may need to change your boat&#;s propeller if it is no longer working or becomes damaged.
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It is important to know the characteristics of your propeller as well as your boat&#;s electric motor. According to these characteristics, you will have to determine the measurements of your propeller if you plan to replace it or ask a dealer for a part.
Before we understand how a propeller is measured, it&#;s best to review the essential measurements you need to know to define its size.
The diameter of a propeller informs how the boat&#;s engine is used. The larger the diameter, the more strain the engine has in starting the blades.
The pitch of a propeller is the distance traveled by the blades during one complete revolution or spin cycle. This measurement is also an essential point since it informs the engine&#;s round per minute (RPM). This information indicates the engine speed and the top speed of the engine.
If you choose a propeller that doesn&#;t match the power of your engine, you risk damaging your boat. It&#;s therefore important to know how to properly measure your boat propeller.
A simple way to calculate a propeller&#;s measurement is to find this information on the equipment itself. Whether you have an inboard motorboat or not, this data is found either on the inside or outside of the hub of your propeller.
It is presented in the following format: 15 X 27.
The first number (15) is the diameter of your propeller and the second (27) is the pitch.
The notation may change depending on the type of engine, the type of propeller and the number of blades.
The calculation of a boat propeller includes the measurement of its diameter and pitch. This information is usually expressed in inches unless stated otherwise. Over time, your propeller&#;s manufacturing labels may weather. In this case, it is possible to manually measure your propeller.
To illustrate the calculation method, we provide an example below. Note that, whatever the result obtained in all the steps, you must always round up and avoid decimals. This will make it easier to choose your propeller when you need to replace it.
For example, if the distance from the hub to the tip is 12.5 inches, then the total diameter will be 25 inches.
In this example, the propeller has a diameter of 25 and a pitch of 29. The information on your propeller would then be 25 X 29 because you need to round up to avoid decimals.
Given these steps, you may as well determine these measurements yourself or use an online boat propellor calculator that help you determine the pitch of your propeller.
Determining the measurements of your propeller before having it replaced is a process that requires some comfort with numbers. Knowing how to determine them allows you to understand the operation and power of your engine, which is an important step in obtaining your Canadian boat license.
To perfect your knowledge, you can register for our online boating course to become more comfortable with the process.
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