Torque Definition

  • Torque: A twisting force causing rotation.

  • Units: Expressed in pounds/feet.

Torque Calculation

  • Formula: Torque=BHP×5252RPMTorque = \frac{BHP \times 5252}{RPM}

  • Key Insights:

    • BHP: Brake Horsepower

    • RPM: Propeller RPM

    • At 5252 RPM, Torque = Horsepower.

    • Below 5252 RPM: Torque > Horsepower.

    • Above 5252 RPM: Torque < Horsepower.

Engine Output Examples

  • Example 1:

    • BHP: 210 at 3000 RPM

    • Torque: 210×52523000=367.64 extlb/ft\frac{210 \times 5252}{3000} = 367.64\ ext{ lb/ft}

  • Reduction Gear: 2:1

    • New RPM: 30002=1500\frac{3000}{2} = 1500

    • Torque: 210×52521500=735.28 extlb/ft\frac{210 \times 5252}{1500} = 735.28\ ext{ lb/ft}

  • Example 2:

    • BHP: 285 at 4150 RPM

    • Torque: 285×52524150=360.67 extlb/ft\frac{285 \times 5252}{4150} = 360.67\ ext{ lb/ft}

  • Reduction Gear: 1.75:1

    • New RPM: 41501.75=2371\frac{4150}{1.75} = 2371

    • Torque: 285×52522371=631.30 extlb/ft\frac{285 \times 5252}{2371} = 631.30\ ext{ lb/ft}

Yanmar Engine Specifications (4JH80)

  • Rated Output: 58.8 kW / 80 mhp

  • Rated Speed: 3200 RPM

  • Displacement: 2 L

  • Cylinders: 4

  • Torque Performance Curves:

    • Max Torque occurs at specific RPM and BHP values.

Practical Calculation Example

  • Given BHP at RPM:

    • 2000 RPM, BHP: 63

    • Torque: 63×52522000≈165.43 extlb/ft\frac{63 \times 5252}{2000} \approx 165.43\ ext{ lb/ft}