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Abstract
The International Maritime Organization (IMO) now has in place a set of metrics which allow the Transport Energy Efficiency (TEE) of the design and operation of ships to be assessed. The TEE is quantified in terms of mass carbon dioxide emitted per tonne.nautical mile, where the mass is usually based on the ship’s displacement.
These metrics are categorised by ship types using historical ships’ TEE data from the large vessel population. The required IMO-regulated performance is to show a progressive year-on-year improvement compared to the average performance of the whole fleet of international ships.
Naval ships are leading diplomatic and functional representatives of their government and as such, the navies of the world are arguably morally bound to adopt best practice and present the best possible image of their country. However, each aval vessel is different: they have a wide range of sizes and a rage of service and top speeds, and so to create a single metric to allow a comparison and regulation is challenging.
Using information from the public domain, a means of setting a valid TEE target values for warships has been developed which makes use of their given hullform displacement and their declared cruise speed as stated for the associated range calculation.
A method for derivation of the warship TEE is proposed which uses fundamental principles to derive the carbon dioxide emitted at the stated cruise speed. The approach includes the Ships Electrical Load (SEL) which is estimated using the IMO equation in this instance. This approach is independent of propulsion configuration and incentivises the design to reduce the SEL as well as to increase the overall propulsion energy efficiency.
To prescribe the required target TEE values, using values derived from existing vessels, 3D contour plots are presented for warships and for naval auxiliaries on diesel engines at their cruise speed. A spatial, contoured distribution plot of TEE versus the vessels’ displacement and cruise speeds, allows targets to be set for vessels with intermediate displacements and speeds. The target TEE value is looked-up from the declared cruise speed and its displacement, the IMO Capacity term.
Separate contour plots for vessels which rely on GT engine power for propulsion and/or power at the nominated cruise speed are also developed.