Choosing a boat propeller is a task where a single-digit error can cost you 20% speed loss Each propeller has a marking on its body that looks like a set of mysterious numbers and letters: 13×19 3R, 10.5×15 4L or 11¼×17 3BWithout understanding these designations, you risk buying a part that either doesn't pull the boat to plane or makes the engine run at its limit.
In this article, we will not only decipher each letter and number in the label, but also show how to pick up a screw for a specific motor and boatYou'll learn why, by avoiding the typical mistakes. Michigan and Solas use different notation systems, how the screw pitch affects fuel consumption, and why it is sometimes more profitable to put a screw with a scalp. smaller diameter, but larger increments A unique solution for heavy aluminum boats with low-power engines.
What do the numbers in the marking of boat propellers mean: basic decoding
Each propeller has three main parameters, separated by the symbol "x" or dash. 13×19 or 10.5-15These numbers are coded. diameter, step sometimes blade-number Three key specifications that determine the behavior of a boat on the water.
Let's look at the example of the designation 11×17 3R:
- 🔹 11 — screw-piece This is the distance between the opposite ends of the blades multiplied by 2. The larger the diameter, the more the screw rakes up the water, but the higher the engine load.
- 🔹 17 — screw-step The theoretical distance that a boat will travel in one full rotation of the propeller (without slipping). Similar to a bicycle: a big step = hard to spin, but faster.
- 🔹 3R — number of blades (3) and direction of rotation (R - right, L - left)For single-engine boats, right-hand rotation is usually used.
Important: Some manufacturers (e.g., Mercury) indicate the pitch in millimeters for low-power motors (up to 15 hp), which may be confusing. 2.42×8.25 means a diameter of 61 mm (2.42′′) and a step of 210 mm (8.25′′).
Table of conformity of markings of screws from different manufacturers
Not all brands adhere to a single standard. Solas and Michigan They can refer to the same screw in different ways, and here's a table that decodes the markings for popular manufacturers:
| Brand | Example of marking | Diameter (inches) | Step (inches) | Paddles/Rotating | Features |
|---|---|---|---|---|---|
| Solas | 11×17 3R | 11 | 17 | 3 blades, right | Standard designation for most screws |
| Michigan | 13×19P | 13 | 19 | 3 blades, right (P) | The letter P/L represents rotation. |
| Mercury | 9.9×10 4L | 9.9 | 10 | 4 blades, left. | For low-power motors, the step can be in mm |
| Yamaha | 12.25×15-G | 12.25 | 15 | 3 blades, right (G) | The letter G/H stands for rotation. |
| Honda | 10×13 3RH | 10 | 13 | 3 blades, right (RH) | RH/LH - right/left rotation |
⚠️ Attention: Screws. Mercury and Yamaha often have additional letter designations after the main parameters (for example, 13×19-VThese letters indicate that screw-piece (V for high-speed boats, S for heavy loaded boats) and can affect the price by 2-3 times.
How the direction of rotation (R/L) affects the boat's handling
The direction of rotation of the screw is a critical parameter that cannot be ignored.R or RH) is used in 90% of single-engine boats, but there are exceptions:
- 🔄 Right rotation (R/RH): the propeller rotates clockwise (when viewed from the stern). Standard for most outboard motors. jet-momentThe one that pulls the boat's nose to the left.
- 🔄 Left rotation (L/LH): the propeller rotates counterclockwise, used on twin-engine boats to compensate for jet torque or on specialized vessels (for example, for water skiing).
- 🔀 Counterrotation screws: a pair of screws with opposite rotation (for example, on the Mercury VeradoEliminate the jet moment and increase efficiency by 10-15%.
If you install a screw with the wrong direction of rotation, the consequences will be catastrophic:
- 🚨 It'll be a move. vibrate at any rate.
- 🚨 The boat will lose manageability - the nose will take you away.
- 🚨 The engine gearbox will fail for Seasons 1-2 because of the wrong load.
If you are not sure about the direction of your motor, look at the counter-arrow (usually next to the propeller) It shows the right direction of rotation.
Rotor Step: How to Choose the Best for Your Boat
The screw's step is parameterIt's a simple rule of thumb, which affects speed, fuel consumption and engine load.
- 📈 Big step. (e.g. 19-23) for the speedboat The boat accelerates more slowly, but it reaches a higher maximum speed.
- 📉 Small step. (e.g. 9-13′′) for the heavy-boatIt's fast acceleration, but it's low top speed.
How do you know if the screw step is wrong?
| A symptom. | Reason. | Decision |
|---|---|---|
| The engine does not gain maximum speed (not enough 5000-5500 rpm) | Step too big | Reduce step by 1-2 inches |
| The engine "twisted" to cut off, but the boat does not accelerate | Step too small | Increase the step by 1-2 inches |
| High-speed vibration | Damaged blades or mismatch of step with load | Check the balance or replace the screw |
⚠️ Attention: If your engine slow-moving Even with a properly designed screw, check:
- 🔧 Status. anticavitational (Curves or damages reduce efficiency by 30%).
- 🔧 Corner trimming (Optimally - 3-5 ° up on planing).
- 🔧 Boat weight (each) 100 kg of cargo Require a step reduction of 1 inch).
The engine is gaining maximum speed (5000-5500 for two-stroke, 5500-6000 for four-stroke)
Boat goes to planing in 3-5 seconds |
No vibration at high revs |
Fuel consumption corresponds to data-sheet figures.
Rotor diameter: why more isn't always better
The diameter of the screw determines how much water it can capture in one revolution, and it would seem that the larger the diameter, the better the thrust.
- ⚓ Too big a diameter. (e.g., 15′′ per 30 hp engine) will result in:
- 🔥 Overheating of the engine due to increased load.
- 🐢 Loss of top speed by 10-15%.
- 💸 Increase fuel consumption by 20-30%.
- ⚓ Too small a diameter. (e.g., 9′′ to 115 hp) will not be able to transfer power efficiently, and the boat will “twist”.
Motor manufacturers always point out propeller diameter Instructions, for example, for Yamaha F50 The optimum diameter is 10-12 inches, exceeding this value by 1-2 inches is permissible only for heavy aluminum boats or when towing.
How to measure the diameter of the screw without marking?
If the marking is worn, take a bar or ruler and measure the distance from the center of the hub to the end of the blade. Multiply the result by 2, that's the diameter. For example, if from center to edge 15 cm (6 inches), the screw diameter is 12 inches.
Labeling blades: why 3, 4 or 5 – and what it changes
The number of blades directly affects the traction, vibration and speed-upHere's what you need to know:
- 🍀 3 blades The best balance between speed and thrust, is suitable for 90% of boats.
- 🍀 4 blades - better for heavy boats or towing. 10-15% more traction at low speeds, but lose 3-5% of the maximum speed.
- 🍀 5 blades Specialized propellers for professional towboats or racing boats require a powerful motor (from 150 hp) and accurate balancing.
⚠️ Attention: Increased number of blades It does not replace the correct step selection.For example, if your motor does not gain momentum with a 3-blade propeller 13×19, a 4-blade replacement 13×19 won't solve the problem - You need to reduce the step to 13×17.
Manufacturers often add letter designations to the number of blades:
- 🔹 R (Right) Right spin.
- 🔹 L (Left) Left rotation.
- 🔹 C Cleaver is a clover profile of a blade for high-speed boats.
- 🔹 S (Stainless) - screw made of stainless steel (strengther than aluminum by 30%).
Additional designations: what the letters hide after the numbers
In addition to the basic parameters, additional letters and numbers may be found in the screw markings.
- 🔧 Materials:
- 🅰️ A Aluminum (the most common, cheap, but less durable).
- 🆂 S - stainless steel (more expensive, but efficiency is higher by 5-10%).
- 🅱️ B bronze (used in salt water).
- 🔧 Profile of the blade:
- 🅲 C - "clover" profile (for high-speed boats).
- 🅿️ P Progressive step (step increases from hub to edge).
- 🔧 Series of screws:
- 🅱️ Black ooh Solas) - screws with anti-corrosion coating.
- 🅱️ Vengeance ooh Mercury) - high-performance propellers for racing.
Example of decoding complex marking: Solas 12×15 4R-AS:
- 🔹 12×15 - diameter 12′′, step 15′′.
- 🔹 4R - 4 blades, right rotation.
- 🔹 A - aluminum.
- 🔹 S series Stainless (Although the screw is aluminum, here is the designation about the shape of the blades).
If there is a letter in the marking SBut the screw is magnetized -- it's a fake. Stainless steel is not magnetized.
FAQ: Frequent questions about boat propeller marking
🔍 How to determine the pitch of the screw if the marking is erased?
There are two ways:
- 📏 Measure the angle of the blade:
- Put the screw on a flat surface.
- Put the ruler under the edge of the blade so that it lies horizontally.
- Measure the distance from the surface to the next blade (in inches) – this will be the step.
- Step (inches) ≈ (max. boat speed in knots × 1.15) / (Motor turn × 0.85).
- Example: If the boat goes 30 knots by 5000 rpm, then the step ≈ (30 × 1.15) / (5000 × 0.85) ≈ 16′′.
⚠️ Can I install a larger diameter propeller than the engine manufacturer recommends?
You can, but with reservations:
- 🔹 Increase in diameter by 1 inch It is permissible for heavy aluminum boats or when towing.
- 🔹 Exceeding by more than 1.5 inches will lead to overloading of the gearbox and overheating of the engine.
- 🔹 For the latest generation four-stroke motors (e.g., Honda BF150) it is better not to deviate from the recommendations - their gearboxes are sensitive to load.
⚠️ Critical moment: If after the replacement of the screw the engine does not collect minimum recommended speeds (e.g., 5000 for a two-stroke 50 hp), the diameter or pitch is too large.
🔄 What happens if you put a left-handed screw on the right-hand engine?
Consequences:
- 💥 It'll be a move. vibrate It's already idling.
- 🔧 The gearbox will fail for 10 to 20 hours of motors because of the wrong load.
- 🚤 The boat will become runaway - the nose will take you away.
🔧 How to fix it: Just replacing the screw with the right one. No amount of "rework" will help.
🛠️ Which screw is better: aluminum or stainless?
| Parameter | aluminum | Stainless steel |
|---|---|---|
| Price. | Low (from 5,000 )) | High (from 20,000 )) |
| Strength | Soft, bends on impact | Strong, but breaks when hit hard |
| Efficiency | Lower 5-10% | Higher than 5-10% |
| Repairs | Easy hammering. | Not repaired (replacement only) |
| For whom? | Fishermen, amateurs, shallow waters | Sports boats, professionals |
💡 Advice: If you walk on rocky rivers often, take an aluminum screw, it will soften the impacts. Stainless steel is optimal for high-speed boats and sea water.
📌 Where to find the recommended propeller for your engine?
Sources:
- 📄 Instructions for the engine - There is usually a table with recommended propellers for different boats.
- 🌐 Official website of the manufacturer:
- Mercury:
www.mercurymarine.com/prop-selector - Yamaha:
www.yamahaoutboards.com/propeller-guide - Solas:
www.solaspropellers.com/prop-finder
- Mercury:
- 📱 Mobile applications:
- PropFinder for Mercury).
- Yamaha Prop Guide.
⚠️ Attention: Online calculators give approximate For accurate selection, you need a test drive with a tachometer.