MERCURY 48-78239A4 Propeller Rh Spline 48-73982-21 3/4

( Manufacturer Part Number: 48-78239A4 ), ( Part Type: Propeller ), ( Propeller Rotation: Left Hand, Standard ), ( Country Of Origin: United States )

Review MERCURY Propellers Stainless Propeller 3/4 Rh Spline fits 2013–2021

The **Mercury 48-78239A4** and **48-73982-21** propellers are precision-engineered marine propellers designed specifically for high-performance Mercury outboard engines, offering an optimal balance of efficiency, durability, and thrust for both recreational and performance-oriented applications. These propellers are part of Mercury s **13 3/4-inch pitch series**, featuring a **21-inch diameter** with a **15-spline RH (right-hand) shaft connection**, making them ideal for mid-sized outboards ranging from 150 to 250 horsepower. Crafted from high-grade, corrosion-resistant materials, these propellers incorporate advanced hydrodynamic blade designs that minimize cavitation and maximize water flow, ensuring superior fuel efficiency and smooth operation even under heavy loads. The **A4** model in the 48-78239 series is particularly well-suited for applications requiring a blend of speed and towing capability, while the **48-73982-21** is optimized for general boating, offering a refined pitch that enhances acceleration and handling in both calm and choppy conditions. Both propellers feature **Mercury s proprietary blade shaping technology**, which reduces drag and improves overall performance while maintaining structural integrity under demanding use. Whether used on a sportfishing boat, a wakeboard rig, or a versatile cruiser, these propellers deliver reliable thrust and responsiveness, making them a trusted choice for anglers, racers, and weekend warriors alike. Their precise engineering ensures longevity, with robust construction that resists warping, bending, and corrosion key factors in extending the lifespan of your Mercury outboard. For those seeking a propeller that combines performance, durability, and compatibility with Mercury s engine lineup, the **48-78239A4** and **48-73982-21** are exceptional additions to any marine setup.

### **Pros and Cons of Buying Mercury 48-78239A4 and 48-73982-21 Propellers (13 3/4" x 21 RH, 15 Spline)**

#### **Overview**

The **Mercury 48-78239A4** and **48-73982-21** are high-performance propellers designed for Mercury outboard engines, specifically for models with a **15-spline shaft**. These propellers are part of Mercury s **PowerMax** series, known for improved efficiency, fuel savings, and better handling. The **13 3/4" x 21 RH (Right Hand)** pitch is common for mid-sized outboards (typically 150 250 HP range), offering a balance between speed and maneuverability.

---

### **Pros**

1. **Improved Fuel Efficiency**

- Mercury s PowerMax propellers are engineered to reduce drag and optimize water flow, leading to **better fuel economy** compared to older designs.

- The **aerodynamic blade shape** minimizes turbulence, reducing engine strain and improving overall performance.

2. **Enhanced Speed and Performance**

- The **21-inch pitch** provides a good balance between **planing speed and acceleration**, making it suitable for both cruising and light planing.

- The **13 3/4" diameter** is ideal for mid-sized boats, offering a **sweet spot** between handling and top-end speed without excessive cavitation.

3. **Better Handling and Maneuverability**

- The **right-hand rotation (RH)** is standard for most Mercury outboards, ensuring **consistent steering response** without requiring propeller changes.

- The **optimized blade design** reduces "porpoising" (bouncing) at higher speeds, leading to a **smoother ride**.

4. **Durability and Corrosion Resistance**

- Mercury propellers are made from **high-grade stainless steel**, resistant to **corrosion, saltwater, and wear**.

- The **precision machining** ensures long-term reliability, reducing the need for frequent replacements.

5. **Compatibility with Mercury Outboards**

- These propellers are **directly engineered for Mercury s 15-spline shaft**, ensuring a **secure fit** and proper alignment.

- They are part of Mercury s **authorized replacement line**, meaning they meet the manufacturer s performance standards.

6. **Reduced Engine Strain**

- The **efficient blade design** helps the engine operate at **optimal RPM**, reducing wear on internal components.

- This can **extend engine life** and lower maintenance costs over time.

7. **Easy Installation and Replacement**

- Mercury propellers are designed for **quick and straightforward installation**, requiring minimal tools.

- Many dealers offer **installation services**, making it convenient for boat owners.

8. **Warranty Coverage**

- Mercury propellers typically come with a **limited warranty** (varies by model and region), providing peace of mind against defects.

---

### **Cons**

1. **Higher Upfront Cost**

- Compared to **generic or aftermarket propellers**, Mercury s PowerMax models are **more expensive**.

- Prices can range from **$300 $600 **, depending on the dealer and any additional features.

2. **Potential for Overkill on Smaller Engines**

- If installed on a **lower-HP engine (e.g., 115 150 HP)**, the **21-inch pitch may feel too aggressive**, leading to **excessive RPM and rough planing**.

- A slightly smaller pitch (e.g., 20-inch) might be more suitable for **smaller boats**.

3. **Limited Customization Options**

- Unlike some aftermarket brands, Mercury propellers offer **fewer pitch and diameter variations**, which may restrict tuning for specific boat setups.

- If a boat requires **unique performance adjustments**, third-party propellers might be necessary.

4. **Weight Consideration**

- Stainless steel propellers are **heavier than aluminum or plastic alternatives**, which could slightly affect **boat handling in rough water**.

- However, the weight is generally negligible for most recreational boats.

5. **Dealer Dependency for Authentic Parts**

- While Mercury propellers are widely available, **some smaller dealers may not stock them**, requiring online ordering or special requests.

- Counterfeit or non-OEM propellers (common in some markets) may **not perform as expected** and could void warranties.

6. **Potential for Cavitation at High Speeds**

- On **larger boats or high-HP setups**, the **13 3/4" diameter** may cause **cavitation** (bubbling noise) if pushed too hard, reducing efficiency.

- A **larger diameter (e.g., 14" or 15")** might be better for **heavier loads or towing**.

7. **Not Ideal for Deep-V or Extreme Angles**

- These propellers are optimized for **traditional V-drives and stern drives**, not necessarily **deep-V hulls** or **extreme angles**.

- Some boat owners report **reduced performance** on aggressive hull designs without proper tuning.

---

### **Conclusion**

The **Mercury 48-78239A4 and 48-73982-21 propellers (13 3/4" x 21 RH, 15 spline)** are **high-quality, performance-oriented propellers** that offer **significant benefits in fuel efficiency, handling, and durability**. They are an **excellent choice for Mercury outboard owners** looking to **optimize their boat s performance** without sacrificing reliability.

However, they are **not a one-size-fits-all solution**. Boaters with **smaller engines, deep-V hulls, or specific tuning needs** may find that a **different pitch or diameter** would be more suitable. Additionally, the **higher cost** compared to generic propellers must be weighed against the **long-term savings in fuel and engine wear**.

If you are **certain about the engine size, boat type, and intended use**, these propellers will **deliver measurable improvements** in speed, fuel economy, and smoothness. For **custom tuning or extreme conditions**, consulting a **propeller specialist** before purchase is advisable.

---

### **Final Recommendation**

You have a **Mercury outboard (150 250 HP range)** with a **15-spline shaft**.

Your boat is a **traditional V-drive or stern drive** (not deep-V or extreme angle).

You want **better fuel efficiency, smoother handling, and reduced engine strain**.

You are willing to **invest in a high-quality, long-lasting propeller** with warranty support.

Your engine is **below 150 HP** (a smaller pitch may be better).

Your boat has a **deep-V hull or aggressive angle** (a larger diameter may be needed).

You are on a **tight budget** (generic propellers may suffice for basic use).

You need **custom tuning** (third-party propellers offer more pitch/diameter options).

- **Consult your Mercury dealer** or a **propeller tuning expert** to confirm the **optimal pitch and diameter** for your specific boat and engine.

- **Test the propellers** for a few outings to ensure they meet your performance expectations before committing long-term.

- **Store them properly** when not in use to prevent corrosion.

For most **standard Mercury outboard owners** looking for **reliable, high-performance propellers**, these are a **strong recommendation**.

Details:

Up for sale is a Mercury Propellers stainless cleaver propeller part number 48-73982-21 / 48-78239A4. Rotation: Right Hand RH. Hub: 15 splines with pressed in hub. Material: Stainless Steel.

part #: 4878239a4 prices

• $94.99-$169.99

specifications propboapar:

• for makes: Mercury
• for years: 2013-2021
• mpn: 48-78239a4
• part type: Propeller
• propeller rotation: Left Hand, Standard
• country of origin: United States

offer propboapar:

• sold: 0
• options: Ship-to-home
• availability: In Stock
• started: April 4, 2026
• quantity: 1

payments propboapar:

• wallet: Apple-pay
• other
• credit card: Discover

returns propboapar:

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

general propboapar:

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

shipping propboapar:

• service: Standard
• class: Standard
• cost: $0.00
• transit: 4-9 Days
• type: Fixed

seller propboapar:

• city: Mesa, Arizona
• # reviews: 13192
• rating: 100.0%

Mercury 48-78239A4 Is Similar To:

• 031021 Michigan Wheel Aluminum Propeller For Mercury (29% similar) New but a few nicks and scratches from sitting in storage for years. Was a spare...(October 31st, 2018)
• 031027 Michigan Wheel Mercury Propeller Pitch Rh Prop Rebuilt (32.7% similar) Most of my vintage items need cleaned as I sell them in found condition. Mercury propeller 13. Don't hesitate to make me an offer. I do combine shipping...(April 24th, 2018)
• 031053 Michigan Wheel Mercury Force Outboard Aluminum Propeller Blue (36.4% similar) New prop with a couple small nicks from being moved around. Clean, quality, inspected parts...(July 18th, 2018)
• 031061 Michigan Wheel Aluminum Propeller For Mercury (27.5% similar) Contact me, I have something almost any. Marketing, listing apps, application...(June 15th, 2018)
• 031068 Michigan Wheel Match Propeller Rh Mercury Mariner Hp Part (32% similar) Comes with accessories pictured...(August 31st, 2018)
• 031143 Michigan Wheel Match Propeller For Mercury Mariner Searay (30.7% similar) ...(December 22nd, 2018)
• 032054 Michigan Wheel Match New Pitch Blade Boat Propeller Mercury Mariner (28.8% similar) 9 hp 2 stroke NEWER9. Match propeller features include:precision balanced blades, high gloss black powder coat finish,quality aluminum alloy for strength and durability fits mercury mariner OUTBOARDS6, 8...(January 6th, 2019)
• 033003-1 48-79794a4 Michigan Wheel Mercury Hp Stainless Prop Spline (40.5% similar) 1998 mercury 135 hp optic max stainless steel prop x 17 pitch rh MN 135XLOP Sn 0G699776 pn, 48-79794A4...(May 5th, 2018)
• 033006-1 Ssm-253 Michigan Wheel Mi Stainless Steel Propeller Mercury (33.8% similar) ...(June 4th, 2018)
• 033012 Michigan Wheel Edge Stainless Steel Propeller Mercury (37% similar) Propeller is in great used condition x 21 stainless steel complete with hub...(March 22nd, 2019)
• 033019 Michigan Wheel Mi Stainless Steel Propeller For Mercury (39.2% similar) Looking for a specific propeller. Contact me, I have something almost any application. Marketing, listing apps, application...(July 13th, 2018)