Quasi-Propulsive Coefficient η_D
Quasi-propulsive coefficient η_D = η_H × η_O × η_R - the ratio between effective power (EHP) and delivered power (DHP).
Hull efficiency η_H
1.171 -
QPC η_D
0.777 -
Formula, assumptions, and limits
η_D typically 0.60–0.75 for merchant ships. Low η_O (small propeller) compensated by η_H > 1. Improved by ESDs (η_R up 1–3 %) or increased propeller diameter.
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| Thrust deduction | - | ship-propeller interaction | |
| Wake fraction | - | Taylor or Harvald | |
| Open-water efficiency | - | propeller chart | |
| Relative rotative efficiency | - | model test |