Fuel efficiency

Maritime technologies fuel efficiency quick guide

The Shipping Efficiency Clean Tech Guide gives an easy to digest scope of the emission reduction technologies available and their associated fuel saving potential.

This is a simplified but comprehensive reference tool to enable rapid assessment of the fuel saving percentages of the main ship efficiency technologies. To be taken with caution, as no doubt some technology potential seems to be over estimated, like solar for instance.

Nevertheless, a useful document to make sense on technology development likelihood (since fuel represent the main part of shipping lines fixed cost), fuel savings being the main driver for any future development.


Slow steaming a long term viable option

A good presentation from Wartsilla explaining the inital challenges faced by 2 stokes engines to perform slow steaming as makers had designed those engines for a much higher load.

The optimal load range of the two-stroke engine lies between 70-85%. The fuel efficiency of the engine, its operational parameters, the specification of the turbochargers, coolers, auxiliary systems, exhaust gas boilers, and so on, are chosen and optimised for that normal load range. It is natural, therefore, that when the engine is operated continuously in a load range below or even far below 60%, the overall system is no longer fully optimised.

However shipping lines can save a lot bunker tons (and x3 of CO2 emissions) by reducing ship speed. As an example reducing speed from 27 to 22 knots (-19%) will reduce the engine power to 42% of its nominal output (CMCR). This results in hourly main engine fuel oil savings of approximately 58%. A further reduction down to 18 knots saves as much as 75% of the fuel.

Wartsilla after due considerations concluded that the modern two-stroke engines are able to reliably operate in all load ranges between 10% CMCR and 100% CMCR without major modifications, if recommendations are followed.

The possible consequences of continuously operating at reduced load without taking the recommended precautions are:

  • Lower air flows A problematic area after the auxiliary blowers cut out / before they cut in. The possibility of very high exhaust, and thus component temperatures.
  • Poor combustion Poor atomisation. Higher sac volume: injected volume ratio, increased likelihood of dripping. Increased fouling and carbon deposits likely.
  • Cold corrosion Caused by condensation of corrosive vapours. Possible when observing very low engine temperatures during very low load operation.
  • Fouling Of the exhaust system, turbochargers, exhaust boilers Z Of the scavenging air space due to excess cylinder oil. Apart from these engine related concerns, concerns have also been voiced about efficiency losses (e.g. propeller, turbochargers, shaft generators, heat recovery systems) and the accelerated deterioration of condition and performance (e.g. fouling of the hull and propeller due to reduced ship speed, stern tube seals, shaft bearings).

The presentation can be found here: