How can hull friction be reduced, and what is eddy-making resistance compared with eddy-current testing?
Short answer
| Measure | What it attacks |
|---|---|
| Hull cleaning in dock and in water | Marine fouling that raises roughness |
| Anti-fouling or foul-release coating, low roughness | Growth and surface roughness |
| Propeller polishing | Propeller roughness and lost efficiency |
| Air lubrication | Hull-to-water frictional contact |
| Optimum trim and slow steaming, performance monitoring | Wetted surface and speed |
- Why: frictional resistance is the largest component at service speed; it rises with wetted area, roughness and about speed to the 1.8 power, so it drives fuel and CO2.
- Reduce friction: clean hull, anti-fouling or foul-release coating, low roughness, polished propeller, air lubrication, optimum trim and slow steaming with performance monitoring.
- Eddy-making (form) resistance: flow separates at abrupt changes of form (stern, appendages) and sheds eddies; reduced by streamlining and faired appendages.
- Other meaning: eddy-current testing is NDT: an alternating-current coil induces eddy currents and a surface crack disturbs them (shafts, tubes, welds).
- Trap: in a resistance question the examiner means eddy-making resistance, not the NDT method.
- As Chief Engineer: a clean, smooth hull and propeller plus trim and speed management are SEEMP measures that cut fuel directly.
Full answer
The full answer explains each point step by step, with the regulations and figures behind it and the discussion from other candidates. It is in the MEO Class I section of the Marine One forum, open to members enrolled for the MEO Class I exam.