The propeller is the heart of the outboard motor, which is responsible for 80 percent of your boat's performance. The wrong choice can lead to overheating, loss of speed, or even failure of the gearbox. But how do you find the same propeller among hundreds of models that will unlock your boat's potential?

Many owners mistakenly believe that it is enough to buy a screw "on the power of the engine" or "like the neighbor." diameter, step, material, blade-number even boat-lineFor example, a heavy aluminum boat with an engine. Yamaha F25 It's going to require a smaller pitch propeller than a lightweight PVC boat with the same engine, and trolling fishing requires a very different approach than speeding.

In this article, we will discuss screw-workWe can read the labels, compare the materials, and give ready-made recommendations for popular boat-motor combinations. Without water and general phrases, only specific numbers and proven matching schemes.

1. The main parameters of the propeller: what do the numbers on the blades mean

Each screw has a type marking engraved on it. 10×13 3R or 9.25×11 4BThis is not a random set of numbers, but the key specifications that determine the behavior of a boat on the water.

First number (diameter) This is the diameter of the circle that the blade tips describe. It's measured in inches. 10" 25.4 cm The diameter depends on:

  • 🔹 Traction force - the larger the diameter, the stronger the screw "pulls" the boat from the spot, but the higher the load on the engine.
  • 🔹 Maximum speed Large screws are worse unwind at high speeds, limiting the “ceiling” of speed.
  • 🔹 Depth of immersion It is important for long-dated engines (e.g., Mercury 15 with legs of 20-25 inches.

Second number (step) The theoretical distance that the screw travels in one complete revolution in a solid medium (like a screw in a tree). On water, because of slippage, the real step is always smaller.

  • 🔸 Speed specifications - a large step (for example, 15") gives high speed but requires a powerful motor.
  • 🔸 Engine load If the pitch is too large, the engine will not be able to spin the screw to working turns (the risk of overheating).
  • 🔸 Fuel economy The optimal step reduces fuel consumption by 10-15%.

Letters after numbers The number of blades (3R - 3 blades, 4B Three-bladed propellers are versatile, four-bladed propellers are better for heavy boats or trolling, and five-bladed propellers are used for racing boats.

📊 What kind of screw do you have now?
Standard (staff)
Aluminum postmarket
Stainless
Homemade
I know.

2. How the screw pitch affects engine speed: the rule of "200-500"

The main secret of the screw selection is step-to-stepManufacturers indicate the recommended speed range for maximum power (e.g., Honda BF20 If the screw is not selected correctly, the engine will:

  • 🔴 Untwisted (revs below normal) is a step too big. Symptoms: the engine choking, bad on the glider, overheating.
  • 🟢 twist (overturns) - too small a step, symptoms: high fuel consumption, vibration, risk of damage to the piston group.

A rule of practice: optimal propeller allows the motor to go 200-500 rpm above the upper limit of the recommended range when the boat is fully loadedFor example, for Suzuki DF9.9 with a range of 5000-5500 rpm, the ideal screw will give 5700-6000 rpm at maximum gas.

How to check the current screw:

  1. Load the boat as normal operation (people, equipment, fuel).
  2. Accelerate to maximum speed on level water.
  3. Measure the speed with a tachometer (or through the onboard computer of the motor).
  4. Compare it with the motor passport.

Load the boat under real weight |

Ensure there is no current/wind |

Accelerate to maximum for 3-5 seconds |

Record tachometer speeds |

Compared to the motor range of the passport

⚠️ Attention: Don't confuse maximum speed with workers! Tohatsu M9.8 It can physically spin up to 6500 rpm, but its operating range is 5000-5500. Prolonged work at the maximum speed reduces the engine life by 2-3 times.

3. Aluminum vs Stainless Steel: Which Screw Material Is Better

The material of the propeller affects not only the price, but also the specifications of the boat.

Parameter Aluminum screw Stainless screw
💰 Price. From 3,000 From 15,000
⚡ Strength Soft, bends when hit. Strong, but breaks when hit hard
⚖️ Weight. Lightweight (30-40% lighter than stainless steel) Heavy (increases the load on the gearbox)
🔧 Repairability Easy hammering. Requires professional repairs
⚡ Efficiency Worse keeps speed on plane 5-10% higher efficiency, better acceleration

When to choose aluminum:

  • 🛶 For budget engines up to 15 hp (for example, Parsun T2.6 or HDX T9.8).
  • 🌊 For shallow water and risk of hitting rocks.
  • 🔄 For experimentation with step (cheaper to change).

When you need stainless steel:

  • 🏆 For speed boats (racing propellers) Mercury Racing or Solas Rubex).
  • 💪 For engines from 25 hp and heavy boats (aluminum or fiberglass).
  • 🛠️ For long-term use (serves 3-5 times longer than aluminum).
💡

If you often walk on unfamiliar water bodies, choose an aluminum screw with a silk. rubber-dumper at the hub (e.g., Solas Amita 3It reduces the impact loads on the gearbox when it hits obstacles.

4. Selection of propellers by boat type: PVC, aluminum, fiberglass

The weight and shape of the boat dictate the requirements for the propeller is as much as the power of the engine.

PVC boats (inflatable)

  • 🛥️ Weight: 30-80 kg (lungs).
  • 🔹 Recommended step: 1-2 inches more than the standard (for example, for Mercury 9.9 instead 9.25×9 better 9.25×11).
  • 🔄 Features: because of the soft bottom, up to 15% of thrust is lost - compensated by an increase in pitch.

Aluminum boats

  • 🛥️ Weight: 100-300 kg (medium and heavy).
  • 🔹 Recommended step: 1 inch less than the standard (for example, for Yamaha F25 instead 10×13 better 10×12).
  • 🔄 Features: require screws with a larger diameter (10–11) for better “hook” water.

Fiberglass and boats

  • 🛥️ Weight: 300 kg.
  • 🔹 Recommended step: standard or 1 inch more (depending on the contours of the case).
  • 🔄 Features: 4-5 blade screws are often used to reduce cavitation (for example, Michigan Wheel Apollo).

Example of calculation for a popular boat The winger 360 motorized Honda BF20>:

  • Weight of the boat + engine + 2 people: ~250 kg.
  • Standard screw for BF20: 9.25×11 (aluminum)
  • Optimal screw: 10×10 (Increased diameter for thrust, reduced pitch for heavy boats).
Why should not stainless propellers be installed on PVC boats?

Stainless steel is heavier than aluminum, which increases the load on the PVC boat trunk mounting. In addition, due to the flexibility of the inflatable floor, a stainless screw will not increase speed, but will cost 3-4 times more expensive. Bombard Commando>).

5. How to calculate the optimal pitch of the screw: formulas and online calculators

Use the exact step selection smith (simplified version):

Optimal step (inches) = (max. engine speed × 7560) / (max. boat speed in knots × Gear-ratio gearbox)

Where:

  • Gear-ratio gear ratio of the gearbox (e.g., 2.08 for Mercury 15).
  • Max, speed. The speed of your boat (measured by GPS, not the speedometer of the motor!)

Example for a boat with a speed of 30 km/h (16 knots) and a motor Tohatsu M18 (Gear-ratio 2.08, max revolutions 5500):

Step = (5500 × 7560) / (16 × 2.08) ≈ 12.8 inches

The nearest standard size. 13".

Alternative methods:

  • 📊 Online calculators: Mercury Prop Finder or Solas Propeller Selector.
  • 📏 Practical tests: Buy a screw with adjustable pitch (for example, Solas HR3) and select the optimal angle of the blades experimentally.
⚠️ Attention: If the engine doesn't gain momentum after the rotor is replaced, don't be in a hurry to change the step!
  • 🔧 The condition of the anode on the gearbox (worn anode increases resistance).
  • 🛢️ Fuel quality (bad gasoline reduces power by 10-15%)
  • 🌡️ Engine temperature (overheating limits speed).

6. Top 5 mistakes when choosing a screw (and how to avoid them)

Even experienced water-engineers sometimes make mistakes.

  1. Buying a screw "by eye" Always test the current propeller with a tachometer before replacing it!
  2. Ignoring the weight of the boatAn additional 100 kg of cargo may require a step reduction of 1-1.5 inches.
  3. Savings on balancingThe unbalanced screw vibrates, which causes wear on gear bearings.
  4. Installation of a stainless screw on a weak engine. For example, Parsun T3.6 will not pull heavy stainless steel - the turnover will fall by 20-30%.
  5. Neglecting height above waterIf the propeller is submerged to less than 50% of the diameter, up to 40% of the thrust is lost.

How to avoid mistakes:

Measure the current propeller |

Consider the real weight of the boat with cargo |

Consult with the seller on a specific model of the engine |

Check the balance of the new screw |

Make sure the sleeve is compatible with the gearbox.

We analyzed the feedback from owners and tests from independent experts (including the channel). BoatTest.com) and have compiled a rating of the screws for budget engines:

Motor. Recommended screw Price, RUB Features
Yamaha F9.9 Solas Amita 3 9.25×11 3R 4 500 Universal aluminum for PVC boats
Mercury F15 Michigan Wheel 10×12 3B 22 000 Stainless steel for aluminum boats (adds 3-5 km / h)
Honda BF20 Mercury Black Max 10×13 4B 18 000 4 blades for heavy boats and trolling
Tohatsu M9.8 Solas HR3 9.25×9-13 3R 8 000 Adjustable step (suitable for experiments)
Parsun T9.9 Quicksilver 9.9×10 3R 3 800 Budget aluminum for shallow water

For power motors 25-30 hp. (for example, Suzuki DF30 or Evinrude E-TEC 30) We recommend stainless screws with a diameter of 11-12" and increments of 13-15".

  • 🥇 Mercury Enertia - for speedboats.
  • 🥈 Solas Rubex The best price/quality ratio.
  • 🥉 Michigan Wheel Apollo - for heavy aluminum boats.
💡

For engines 25-30 hp. transition from aluminum to stainless steel gives an increase in speed by 5-10 km / h, but requires checking the gearbox for wear (load increases).

FAQ: Answers to frequent questions

Can I put a screw with a different diameter than the regular one?

Yes, but with reservations: A 0.5-1 diameter increase improves traction, but requires checking the gap between the screw and the anti-cavitation stove (should be ≥15 mm). Mercury 15 screws of 9.25-10 diameter may be safely used. "

Which screw is better for trolling fishing?

For trolling, you need screws with large diameter and small step (for example, 10×8 4B for Yamaha F25Four blades provide smooth running at low speeds (2-5 km/h).

  • 🎣 Mercury Trolling Master (specially for trolling).
  • 🎣 Solas SD314 (budgetary option).
What happens if you put a screw with a bigger pitch than necessary?

The engine won't be able to spin the screw to a full speed.

  • ❌ The maximum speed drop is 10-30%.
  • ❌ Overheating of the engine (temperature rises by 10-15 C).
  • ❌ Increase in fuel consumption by 15-25%.
  • ❌ Risk of detonation and damage to the piston group.

If after replacing the screw the engine does not gain 80% of the maximum speed, the step is too large.

How to check the balance of the screw at home?

Take the screw by the hub and put it on a sharp object (like a screwdriver) like a swing. If one blade outweighs, you need balancing.

  1. Mark the heavy blade.
  2. Carefully undermine its back side with sandpaper (no more than 1 mm!).
  3. Repeat the check.

An imbalance of more than 2 grams leads to vibration at high revs.

Do I need to register a replacement screw in GIMS?

No, changing the propeller does not require changes to the boat's ticket or registration with the GIMS. However, if you change the engine to a more powerful one (for example, from 9.9 hp to 15 hp), this is considered a conversion and is subject to registration.