transmission notes

Marine Transmission Basics

  • Provides Forward, Neutral, and Reverse.

  • Two main types: Manual and Hydraulic Automatic.

Types of Marine Transmissions

  • Co-Axial, Near Co-Axial, Direct Mount.

  • V-Drive, U-Drive configurations.

  • Various mounting options: Remote, Down Angle, Standard, Direct-mount.

Gear Configurations

  • In-line coaxial: Output shaft in-line with engine driveshaft.

  • Parallel drop-shaft (shallow and deep cases): Offsets below the engine.

  • Down-angle gear: Output angles down relative to engine driveshaft.

Direct-mount V Drive

  • Gear mounts on engine bell housing, output shaft angled down in a V.

  • Space-saving but can cause power loss and access issues.

Remote-mount V Drive

  • Engine facing backward, uses a jackshaft to connect.

  • More flexible but has higher power loss due to friction.

Torque and Power Calculations

  • Torque = (BHP × 5252) / RPM.

  • Max speed relation: Generally, 100 RPM per MPH of boat speed.

  • Reduction gears: Single (one gear pair) and Double (multiple gears).

  • Gear Ratio = Number of teeth on driven gear / Number of teeth on driving gear.

Estimating Propeller RPM and Torque

  • Propeller RPM = Engine RPM / Reduction Ratio.

  • Torque does not increase speed, but thrust for boat movement.

Examples and Applications

  • Max speed calculations based on output power and RPM.

  • Use of reduction gears for optimization in boat speed and performance.