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  3. MERCURY 48-78122A40L

MERCURY 48-78122A40L Rh Boat Prop Pitch Spline 13.75

fits make: Mercury. year: 2015–2021.

48-78122a40l Mercury Aluminum Rh Boat Prop 13.75 X 21 Pitch 15 Spline 78122

( Manufacturer Part Number: 48-78122A40L ), ( Part Type: Aluminum Prop ), ( Propeller Rotation: Standard )

Review MERCURY Aluminum Rh Boat Prop 13.75 Pitch Spline 78122 fits 2015–2021

The **Mercury 48-78122A40L RH Boat Propeller** is a high-performance, precision-engineered propeller designed to deliver exceptional thrust, efficiency, and reliability for marine applications, particularly on outboard engines in the 150 250 horsepower range. Crafted from high-grade aluminum alloy, this **13.75-inch diameter, 21-pitch, 15-spline** propeller features a **right-hand rotation (RH)** design optimized for smooth operation and maximum power transfer, making it ideal for both recreational and light commercial vessels. The **four-blade configuration** balances durability with hydrodynamic efficiency, reducing cavitation and improving fuel economy while maintaining strong acceleration and top-end speed. Its **smooth, contoured blade surfaces** are engineered to minimize drag and turbulence, ensuring consistent performance across a wide RPM range. The **15-spline shaft connection** provides a secure, vibration-dampening fit, reducing wear on the engine s internal components while enhancing overall stability. Whether used on a sportfishing boat, a wakeboard rig, or a versatile cruiser, this propeller excels in delivering crisp throttle response, reduced noise, and enhanced handling making it a standout choice for those seeking a balance of power and precision in their marine propulsion system. Built to Mercury s rigorous standards, it is backed by a reputation for durability and performance, ensuring long-lasting reliability in both calm waters and demanding conditions.

### **Pros and Cons of buying a Mercury 48-78122A40L RH Boat Prop (13.75" Diameter, 21 Pitch, 15 Spline)**

#### **Pros:**

1. **High Performance for Outboard Engines** This propeller is designed for Mercury outboards, ensuring optimized efficiency, speed, and acceleration. It is well-suited for mid-sized boats (typically 18 24 feet) with 150 250 HP engines, delivering strong thrust and fuel economy.

2. **Durable Construction** Made from high-quality stainless steel, this prop is resistant to corrosion, wear, and damage from saltwater, making it ideal for marine use. The robust design helps maintain performance over time.

3. **Balanced Pitch for Versatility** The **21-inch pitch** provides a good balance between speed and torque, making it suitable for both cruising and light planing. It works well for fishing, leisure boating, and general use where moderate speed is preferred over extreme acceleration.

4. **Right-Hand (RH) Rotation** Since this is a **right-hand prop**, it is designed to work with standard Mercury outboards that rotate clockwise when viewed from the stern. This ensures proper alignment with the engine s shaft, reducing strain and improving efficiency.

5. **Standard 15-Spline Shaft Fit** The **15-spline shaft** is a common size for many Mercury outboards, making installation straightforward and reducing the need for custom adapters. This also means it is widely available for replacement or upgrades.

6. **Good for Fuel Efficiency** A well-matched prop like this helps optimize engine performance, reducing fuel consumption while maintaining adequate speed and power. This is beneficial for long trips or frequent use.

7. **Compatibility with Mercury Outboards** Being a **Mercury-specific prop**, it is engineered to work seamlessly with their engine systems, minimizing vibration and maximizing power transfer.

8. **Easier to Find Replacements** Since this is a widely used model, spare parts, replacements, and maintenance tools are readily available through Mercury dealers and marine supply stores.

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#### **Cons:**

1. **Not Ideal for High-Speed Planing** The **21-inch pitch** is moderate, meaning it may not excel in extreme speed or aggressive planing. Boaters looking for high-speed performance (e.g., wakeboarding, water skiing) might need a lower pitch (e.g., 18 20 inches) for better acceleration.

2. **Potential for Cavitation at High Loads** If the engine is heavily loaded (e.g., towing heavy loads or running at high RPMs), this prop may experience cavitation, reducing efficiency and causing noise. A slightly lower pitch might be better in such cases.

3. **Weight Consideration** Stainless steel props are durable but heavier than some aluminum options. While this doesn t affect performance significantly, it may require more effort to remove or install, especially for smaller boats.

4. **Limited to Mercury Outboards** This prop is **not universal**; it is designed exclusively for Mercury engines. Attempting to use it on a different brand (e.g., Yamaha, Suzuki) without proper matching could lead to poor performance or damage.

5. **Cost Relative to Performance** While not excessively expensive, this is a **mid-range prop**, and boaters with extreme performance needs (e.g., racing, heavy towing) might opt for more specialized, higher-end props with better efficiency gains.

6. **Potential for Wear Over Time** Like all props, this one will experience wear from debris, corrosion, or improper use. Regular maintenance (e.g., cleaning, inspection) is necessary to prolong its lifespan.

7. **Installation Requires Care** Improper installation (e.g., misalignment, overtightening) can damage the shaft or prop. Boaters without experience should consult a professional to avoid issues.

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### **Conclusion:**

The **Mercury 48-78122A40L (13.75" x 21" pitch, 15 spline, RH)** is a **reliable, well-balanced propeller** suited for **mid-sized Mercury outboards** in the **150 250 HP range**. It excels in **fishing, cruising, and general boating** where moderate speed and efficiency are prioritized. However, it may fall short for **high-speed planing, heavy towing, or extreme performance applications**, where a different pitch or prop design would be more appropriate.

If your primary use involves **daily fishing, leisure cruising, or light planing**, this prop is a **solid, cost-effective choice** with long-term durability. For **high-performance needs**, consider a prop with a **lower pitch (e.g., 18 20")** or a **custom-machined option** for better acceleration.

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### **Recommendation:** - **Buy this prop if:**

- You have a **Mercury outboard (150 250 HP)**.

- Your boat is **18 24 feet** and used for **fishing, cruising, or light planing**.

- You want a **durable, efficient, and easy-to-find replacement** prop.

- You prioritize **moderate speed and fuel economy** over extreme acceleration.

- **Consider alternatives if:**

- You need **higher speed or aggressive planing** (opt for a **lower pitch, e.g., 18 20"**).

- You frequently **tow heavy loads or use the boat for racing** (a **custom prop** may be better).

- Your engine is **outside the 150 250 HP range** (check Mercury s prop matching guide for the correct size).

- You want **lighter weight** (some aluminum props offer similar performance with less weight).

**Final Verdict:** This is a **good, all-around prop** for standard Mercury outboards in recreational use. Ensure it matches your engine s **HP, shaft size, and intended use** before purchasing. If in doubt, consult a **Mercury dealer or marine mechanic** to confirm compatibility.

Details:

Mercury Aluminum RH Boat Prop 13.75 x 21 Pitch 15 Spline 48-78122A40L 78122. Buyer Pays Return Shipping.

part #: 4878122a40l prices

  • $27.79-$139.99

specifications propboapar:

  • for makes: Mercury
  • for years: 2015-2021
  • mpn: 48-78122a40l
  • part type: Aluminum Prop
  • propeller rotation: Standard

general propboapar:

  • Parts Accessories > Boat Parts > Propellers
  • condition: Used

returns propboapar:

  • time: 14 Days
  • policy: Returns Accepted
  • paid by: Buyer

shipping propboapar:

  • cost: $15.62
  • class: Standard
  • service: USPS Ground Advantage
  • carrier: USPS
  • transit: 9-13 Days
  • type: Calculated

seller propboapar:

  • rating: 99.6%
  • # reviews: 546
  • city: Gravois Mills, Missouri

offer propboapar:

  • availability: In Stock
  • best offers: True
  • quantity: 1
  • sold: 0
  • started: February 18, 2026
  • options: Ship-to-home

payments propboapar:

  • credit card: Diners-club
  • other
  • wallet: Apple-pay
for makes: mercury, for years: 2015-2021, part type: aluminum prop, propeller rotation: standard,
category: boat parts > propellers, sku: 12159184833526793,
Mercury 48-78122A40L Is Similar To:
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5 offers $27.79–$139.99 USD
  • New other (see details). Offer #1 priced at $139.99 + $14.94 shipping estimate = $154.93* total. +$14.94 shipping
  • Used. Offer #2 priced at $27.79 + $20.60 shipping estimate = $48.39* total. +$20.60 shipping
  • Used. Offer #3 priced at $100.00 + $41.15 shipping estimate = $141.15* total. +$41.15 shipping
  • Used. Offer #4 priced at $75.00 + $16.87 shipping estimate = $91.87* total. +$16.87 shipping
  • Used. Offer #5 priced at $35.97 + $20.85 shipping estimate = $56.82* total. Would make a good spare or for repair Fair condition.+$20.85 shipping

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