Marking of screws of outboard motors: full decoding of codes and designations

The right propeller is a critical step in the adjustment of the outboard motor, because it is this unit that converts engine power into traction. Many watercraft owners often face a situation where the motor does not develop the declared power or, conversely, does not pull the heavy boat. The reason is often the inconsistency of the propeller specifications of the real operating conditions. On the surface of the blade, numbers and letters are stamped out that contain all the necessary information to identify the product.

Ability to read these coder It allows the owner to determine whether the current propeller is suitable for him or if he needs to be replaced with a model with a different pitch or diameter. Decoding errors can lead to overheating of the engine, increased fuel consumption and even engine failure. In this article, we will examine in detail all the nuances of marking adopted by leading manufacturers, and learn how to choose the optimal pair of "engine-propeller".

Basic structure of marking on the blades

Each propeller blade, whether it's an aluminum model or a stainless steel product, has a set of symbols that are not random and are standardized for easy identification. Usually, the marking is on the front of the blade, closer to the hub, where the least likely mechanical damage is to be caused by impacts on water obstacles. diameter and step screw.

The diameter of the screw is the distance between the extreme points of opposite blades, measured in inches. The screw pitch is the theoretical distance that the screw would travel in one complete revolution in a solid medium without slipping. These are the two parameters most often listed first in the labeling line. For example, the entry "13 1/4 x 17" means that you have a 13.25 inch screw in 17 increments.

In addition to geometric dimensions, the marking necessarily contains information about the direction of rotation and the number of blades. Standard screws have a right rotation, but for tandem installations or specific tasks, left screws can be used. stainless-steel.

Decoding of letter designations of the direction of rotation

One of the most important things that newcomers often overlook is the direction of rotation of the propeller. R (Right) and L Standard for most single outboard motors is right-hand rotation, which means that the screw turns clockwise when you look at the transom from behind.

If you see a letter L At the end of the marking line, this indicates left rotation, and these propellers are used on two-engine boats (tandem), where one screw has to rotate to the right and the other to the left to compensate for torque and ensure the boat's straight-line course, and placing the left rotor on the right-rotating motor will result in no traction and possible damage to the gearbox.

Sometimes, instead of the letters R and L, you'll find the symbols RH (Right Hand) and LH (Left Hand), which is the complete equivalent. Yamaha or MercuryThe direction code may be embedded in the article of the part, but the screw metal itself will always have an explicit letter R or L for quick visual verification.

• 🌀 R / RH Standard right-hand rotation occurs in 90% of cases on single motors.
• 🔄 L / LH - left rotation, used on twin engines or specialized equipment.
• ⚙️ Counter Rotation A term often used in documentation to refer to reverse rotation screws.

⚠️ Warning: Never attempt to install a left-hand drive on a right-hand drive shaft, even if the landing strands match, which will cause the thrust bearing to collapse instantly and the oil to be ejected from the gearbox.

Manufacturing material and its coding

The material from which the screw is made directly affects its performance, durability and maintainability. In labeling, this is often reflected in additional letters or prefixes in the article. Aluminum screws are the most common due to their low price and ability to deform on impact, protecting the engine's dreaded. AL The absence of special symbols often indicates aluminum.

Stainless steel screws are marked with letters SS They have much less resistance to water, thinner and lighter than aluminum analogues at the same size, which allows you to increase the efficiency of the engine by 5-10%. However, steel does not forgive shocks: when you encounter a solid object, the impact energy is transferred to the gears of the gear gear gear gears of the gear gear. Rubber Hub with damper bushings.

There are also composite screws that are marked in a special way, for example, Comp They combine plastic flexibility when impacted with rigidity when working at high speeds, and when deciphering, it's important to look at the word "Propeller" or "Prop," which confirms the purpose of the part, especially if you buy a used screw without packaging.

Step and diameter coding system

The most difficult part of the marking for beginners is the numerical marking of step and diameter, since manufacturers use different coding systems. Suzuki or TohatsuFor example, the code "15" may mean a step of 15 inches, but sometimes the step is coded in letters.

In the coding system Yamaha There are often double markings: explicit (numbers on the blades) and hidden (code in the catalog). Mercury and Quicksilver It's a system where the pitch can be marked with a P (Pitch) followed by a number, and it's important to understand that the pitch of the screw is not a fixed value for all conditions; it's a geometric parameter that is matched by the weight of the boat and the speed you want.

For a precise decoding of step codes, you need to refer to the manufacturer's matching tables. For example, Suzuki's code "K" can mean step 15, and the code "G" - step 13. An error in the interpretation of even one inch of step can change the maximum engine speed (WOT) by 150-200 rpm, which is critical for the life of the engine.

Manufacturer	Blade marking	Transcription (example)	Type of data
Yamaha	13 1/4 x 17-K	Diameter 13.25", Step 17", Code K	Clear.
Suzuki	11 1/4 x 15	Diameter 11.25", Step 15"	Clear.
Mercury	48-8M0075167	Article (step searched by catalog)	Catalogue
Tohatsu	M10.6D2	Series code and parameters	Hidden

What is a "step reserve"?

The step reserve is the possibility of installing a screw with a large geometric pitch on engines that have a speed limiter or electronic control of the throttle, which allows you to compensate for the loss of speed when the boat is fully loaded.

Specificity of labeling of different manufacturers

Each major outboard motor manufacturer is striving to implement its own marking standards, which creates some confusion when selecting analogues. YamahaFor example, it often uses three-digit codes at the end of the marking that indicate a series of screws (e.g., K, G, J), where each letter corresponds to a specific step in inches, and it is almost impossible to decipher them without a catalog.

Company Mercury In recent years, it has moved to a system where the emphasis is on the part articular number, which is stamped on the hub, and geometric parameters can be specified in small print on the edge of the blade. Michigan WheelThese are popular aftermarket solutions that often have very detailed labeling right on the front, including material and precise pitch with tenths of an inch.

Chinese manufacturers, such as Parsun or HideaThe original motors (Yamaha/Tohatsu) are often copied, but may use simplified designations. It is important to be careful here: the claimed pitch of 10 inches on a Chinese propeller may actually differ from the original by 0.5-1 inches due to casting tolerances.

• 🇯🇵 Japanese brands (Yamaha, Suzuki, Tohatsu) – Prone to use letter codes of step, requiring a reference.
• 🇺🇸 American brands Mercury, Evinrude – often rely on articles and catalogs, less often write a step explicitly.
• 🇨🇳 Chinese analogues - can duplicate the original marking, but require mandatory rechecking of the dimensions with a bar.

Practical Guide to the Selection of Screws

Understanding the markings is only half the battle, and the key is to apply that knowledge to the right screw to unlock the potential of your engine, and the key to getting the engine right is to get to the Wide Open Throttle when the boat is fully loaded, and if the engine doesn't get to the top of the range, the pitch is too high.

If the motor, on the other hand, "twistles" the allowable speed, there is a risk of valve combat (for four-stroke engines) or bully piston group. In this case, you need to increase the pitch of the screw. Each change in step by 1 inch changes the engine speed by about 150-200 units. This "one inch" rule is the gold standard for the initial setting.

Switching from aluminum to stainless steel in the same step will actually increase efficiency, and the motor may start to twist, in which case, when switching to steel, it is recommended to increase the step by 1-2 inches relative to the aluminum prototype to compensate for the increased efficiency.

Frequent errors in reading labels

One of the most common mistakes is the confusion between diameter and pitch. Inexperienced boaters often take the first number per step, although the standard always states the diameter first. This leads to the purchase of a screw with completely inappropriate specifications. Always remember: diameter is the physical size that should correspond to the datant, and step is the performance characteristic.

Another mistake is ignoring the marking state. On old, broken screws, the numbers can be filled with dirt or salts. Trying to read 13 as 18 because of a chip on metal will lead to mismatching. Use a magnifying glass and solvent to clean the surface before reading. It is also important not to confuse the casting number with the part number; the casting number is often on the hub and does not carry information about the step.

You should not rely solely on the visual similarity of the screws of different brands. Yamaha 9.9 may have a completely different blade profile and pitch than the screw from the Tohatsu It has the same digital marking, despite the similarity of the motors, and always check the Part Numbers on the hub.

⚠️ Note: If the marking on the screw is completely erased or not readable, do not try to guess the parameters. Using a screw with unknown pitch can cause the engine to fail on the first launch.

The effect of the screw's pitch on driving performance

Choosing the right pitch is always a trade-off between traction and speed. Small pitch screws (like 7-9 inches) create powerful traction at low revs, ideal for heavy boats, full-load glides or water skis. However, the top speed with such a propeller will be low, since the engine will quickly reach the rev cut-off.

Large pitch propellers (17-21 inches or higher) allow for high top speeds, but plane time increases. If the boat doesn't go into mode for a long time, the fuel consumption in transition will be huge, and engine wear will be critical. So the pitch marking should be read in the context of your vessel's weight.

There is a concept of "universal pitch", which usually comes with a motor (standard propeller). For most PVC boats 3-4 meters long with a 5-10 hp engine, the optimal step is in the area of 9-11 inches. For larger aluminum boats with 15-20 hp engines, the standard step is 11-13 inches.

Can I saw the screw?

Mechanical change of blade geometry (shortening to reduce pitch) is strongly discouraged, disrupting the screw's balance, causing vibrations that destroy the deidvent bearings, and changing the hydrodynamic profile, reducing efficiency.

What to do if the marking on the screw is completely erased?

If the numbers are not readable, the only reliable way to determine the parameters is to measure the pitch manually, so that the screw is laid on a flat surface, and with the help of a conveyor and ruler, the angle of inclination of the blade is measured at a radius of 0.75 from the diameter, but it is easier and cheaper to contact a specialist in the service center, which has templates for checking the step.

Does the number of blades affect the marking?

Yes, the number of blades (3, 4 or 5) is often indicated in the model marking or code. Quaternary screws provide smoother running and better traction at low revs, but have a lower top speed compared to three-bladed counterparts of the same pitch.

Can a large diameter propeller be used if it is suitable for landing?

The increase in the diameter of the screw is possible only if the gap between the blade and the anti-cavitation plate (or the sole of the boat) is at least 10-15% of the diameter of the screw. The reduction of the gap will lead to cavitation, noise and loss of traction.

What does the letter "S" mean at the end of some screws marking?

Depending on the manufacturer, the letter "S" can mean "Stainless" or indicate a special series of screws (for example, Suzuki Special). In some cases, the "S" denotes a standard step (Standard), as opposed to High Pitch (HP).

How often should I change the propeller?

The propeller has no strict shelf life. Aluminum propellers are changed when cracks occur, when edges or chips become severely strained, when they are not corrected. Steel screws last longer, but they require micro-cracking checks. If the propeller is intact and the motor is turning, you don't need to change it even after 10 years.