Figures on the propeller of the outboard motor: full decoding of marking

Every owner of water equipment sooner or later faces the need to replace or select a new propeller. When you look at the hub of the product, you can see knocked out numbers and letters that often seem like a meaningless set of characters for an untrained person. However, these data contain all the necessary information about the geometry of the blade, the material of manufacture and compatibility with a particular motor.

Understanding the marking is not just theoretical knowledge, but a practical skill that saves fuel and saves engine life. Incorrectly selected step or diameter This can cause the piston group to overheat or, conversely, torsion of the crankshaft, which will eventually result in expensive repairs. In this article, we will discuss in detail how to read the "passport" of your screw and what to pay attention to first.

Modern manufacturers, such as Solas, Michigan Wheel or TohatsuThey use standardized notation systems, although they have their own unique features, and once you understand the logic of these notations, you can diagnose problems with planing and find the best solution for your child. water-motor complex No dealing with dealers.

Where to look for a label and what it looks like

Identification is the first step to understanding product specifications. Usually, all the data you need is stamped on the screw hub, which is the center hub where the gearbox shaft is inserted. In some models, especially plastic or composite materials, the information can be deposited with a laser or paint, which eventually erases it.

You will often see a line that resembles a fraction, for example, 10 1/4 x 13This is the basic formula, where the first digit is the diameter and the second digit is the pitch of the screw, but there may be other codes nearby that indicate the number of blades, the direction of rotation or the serial number of the batch. Surface cleanliness In this area is critically important: before trying to read the erased numbers, it is recommended to carefully clean the hub of oxides and dirt, without using abrasive materials.

It's important to note that rubber hub screws may have a deeper, closer to the landing strand, and if you can't find the numbers on the visible part, you may need to remove the screw from the shaft to view it from all sides. Sometimes manufacturers hide the code under a layer of anti-fouling paint, so a thorough visual inspection is required.

Rotor diameter: influence on thrust and speed

The first number on the label always represents the diameter of the propeller, which is the distance between the tips of opposing blades, measured in inches. 13 x 15 The number 13 means that the diameter is 13 inches (about 33 cm). Rotor diameter It directly affects the area of the surface to be swept and therefore the amount of water that the screw can throw back in one turn.

Increasing the diameter tends to lead to lower thrust, which is useful for heavy boats or when using additional equipment. However, too large a diameter can put an excessive load on the engine, preventing it from reaching maximum speed. In turn, a small diameter will allow the engine to unwind more easily, but can lead to loss of efficiency at high speeds and an increase in the risk of cavitation.

When selecting a screw, it is important to consider the gap between the blade tips and the anti-cavitation ring in lower unit. The standard gap is about 10-15% of the diameter of the screw. If you plan to install a larger screw, make sure it physically fits in the screw. motor-gondola without risk of damage to the protective casing or the screw itself during maneuvers.

Rotor step: the main performance parameter

The second number in the fraction represents the pitch of the propeller (Pitch), which is theoretically the distance in inches that the propeller would travel in one complete revolution in a solid medium without slipping, and is the key parameter that determines the balance between the maximum speed of the boat and the speed of its entry into planing mode. Change of step The most effective way to adjust the motor for specific tasks.

There is a direct relationship: a 1-inch reduction in pitch usually leads to an increase in maximum engine speeds by about 150-200 rpm. If your motor does not twist to the upper limit of the range (WOT), you need a screw with a smaller pitch. Conversely, if the engine "twistles" the upper limit, you need to increase the pitch to reduce load and avoid wear.

Some screws are marked with the letter "P" after the step number (for example, 13P), which just confirms the step indication. There are also variable pitch screws, but they are rare and used in specific conditions. For most water motors, the rule is simple: smaller pitch is more traction and acceleration, larger pitch is higher potential speed, but heavier acceleration.

Number of blades and other designations

In addition to the diameter and the pitch, you can often find numbers on the hub indicating the number of blades. 3, 4 or 3 BL (Blades) Three-bladed screws are the most common due to their versatility and high top speed. Four-bladed models provide smoother running, better handling at low speeds and less vibration, but can slightly reduce the "maximum speed."

Rotation direction is also important, and twin-engine or tunnel-propeller boats may use left-hand propellers (see below).Left Hand) and right (Right Hand) rotations. Markings may contain letters LH and RH Installing a propeller with the wrong direction of rotation will cause the boat to move backwards (or vice versa) instead of moving forward, and also cause the engine to overheat due to a violation of the water supply to the cooling system.

Special attention should be paid to the marking of the material. BrAnd aluminum. AlAnd stainless steel, SSSteel screws, having high strength, often have thinner blades, which also affects their hydrodynamic specifications and requires the correct selection of pitch.

Manufacturer-specific codes

Other brands use their own coding systems that can confuse a beginner. Tohatsu frequently 9 1/4 x 10where there may also be a letter indicating a series or type of hub. Yamaha You can find codes that start with a letter. F or KCompatibility with certain models of gearboxes.

Company Solas, which is one of the largest independent manufacturers, uses its own system, where the code may include the name of the series (for example, the name of the series). Amir, HelixThis is important to consider when looking for analogues: a screw with the same pitch and diameter numbers from different manufacturers may have different blade geometry (turning, area), which will lead to different behavior of the boat on the water.

In some cases, there is a marking of the species. A x BWhere A is the diameter in centimeters (rarely, mostly for old Soviet or specific European engines), but 99% of the time the marine engine industry has adopted an inch measurement system. Always double-check the units of measurement if you doubt the origin of the screw.

Table of step and engine speed

To understand how the change in propeller geometry affects engine performance, here is an example table. The data is relevant for standard four-stroke engines with a capacity of 15-60 hp in an average boat load.

And you can see from the table that you can manipulate the step, you can fine-tune the motor, but it's worth remembering that these values are approximate, and the real result depends on the state of the engine, the cleanness of the bottom of the boat, the excitement on the water, and even the temperature of the off-shore water. Accurate setup It is possible only by experiment using a tachometer.

Typical errors in decoding and selection

One of the most common mistakes is to ignore the type of hub. The numbers may match, but if the screw is designed for a hub with a rubber stack, and you have a motor that requires a screw with a slit fit (or vice versa), you can't install it. Also, screws for engines of different power, which may have different diameters of the landing shaft, are often confused.

Another mistake is to try to compensate for power shortages by reducing the pitch, so if the pitch is too small, the engine will run into a cutoff at low speeds, and the boat will not be able to develop enough speed to plane, which will lead to fuel overrun. It is critically important to select the screw so that on a fully open throttle (WOT) the engine goes into the upper third of the operating speed range specified in the instructions.

⚠️ Attention: Never use a screw with cracks, chips on the edges of the blades or a deformity of the hub. Even a microscopic defect can lead to an imbalance and destruction of the screw at high revs, which can damage the gearbox or injury people in the water.

Frequently Asked Questions (FAQ)