Basic knowledge of marine engine, gearbox and propeller matching

In marine propulsion systems, the proper matching of the engine, gearbox (reduction gear) and propeller is crucial. It directly affects the marine power performance, fuel economy, speed and service life.

Ⅰ.Basic Requirements for Marine Engines

1) Classification of Marine Engines

By Fuel Type:

  Diesel engines, gas engines, dual-fuel engines

By Speed:

  Low-speed engines (<300 rpm): Such as large two-stroke diesel engines, applicable to ocean-going cargo ships

  Medium-speed engines (300-4000 rpm): applicable to medium-sized cargo ships, fishing boats, etc.

  High-speed engines (>4000 rpm): applicable to speedboats, warships, yachts

2) Marine Engine Parameters

Rated Power (kW/HP): Determines the propulsion force

Rated Speed (rpm): Requires matching with gearbox and propeller

Torque (Nm): Affects ship acceleration on speed and heavy-load capacity

Fuel Consumption (g/kWh): Determines economic efficiency

Ⅱ.Function and Matching of Gearboxes (Reducers)

1) Function of the Gearbox

Reduction and Torque Boost: Reduces engine speed and increases torque output

Reversing Function: Supports forward/reverse switching

Adaptation to Different Working Conditions: Such as azimuth propulsion, variable pitch propellers etc.

2) Selection of Reduction Ratio

Reduction Ratio = Engine Speed ÷ Propeller Speed

It needs to be calculated based on the propeller diameter, ship speed, and load conditions.

Ⅲ.Propeller Matching Principles

1) Basic Propeller Parameters

Diameter (D): Determines thrust

Pitch (P): Affects speed and efficiency

Number of Blades (Z): Affects vibration and efficiency

Installation Angle (Adjustable/Fixed)

2) Propeller Calculation

Theoretical speed (V) = Rotational speed × Pitch × Efficiency

Cavitation effect, propulsion efficiency, hull resistance, etc. Need to be considered.

Ⅳ.Matching Optimization Strategy

1) Low-speed vessels (e.g. cargo ships, fishing boats)

Choose low-speed or medium-speed diesel engines to improve fuel efficiency.

Choose larger diameter, smaller pitch propellers to increase driving forcing.

Appropriately increase the reduction ratio to optimize torque output.

2) High-speed vessels (e.g., yachts, warships):

Choose high-speed diesel engines to meet high-speed requirements.

Choose smaller diameter, larger pitch propellers to improve propulsion efficiency.

Choose low reduction ratios or direct drive to reduce power loss.

Ⅴ.Conclusion

The proper matching of the engine, gearbox, and propeller is crucial for ensuring efficient ship operation. It is necessary to comprehensively consider power requirements, fuel economy, speed requirements, and hull design. In actual matching, optimization can be achieved by using computational models, ship test data, and CFD simulation analysis.