7.5 Fuel consumption as a function of load
There is not much data available on this issue. In principle the fuel consumption as a function of load for a specific ship is governed by the Admiralty coefficient
Const. = v3 D2/3 /P,
where v is the speed, D the displacement and P the engine power. D can be written as a linear function of the load and thus of LCU. Since ED is assumed to be proportional to P, it will be proportional to the displacement to the power of 2/3 when the speed is constant.
We here define the function F which is ratio the fuel consumption (per km) at a given load and the fuel consumption at full load which can be written as
F (LCU) = (d + e*LCU)2/3.
The IMO GHG study gives emissions in g/tonne-km for the ship types in table on capacity utilization in wiki load capacity utilization both at the utilization factor given in the table and at full load. From these two points d and e can be obtained giving a function that represent the relative decrease in fuel consumption per km with the load lower than full down to the utilisation factor.
The function F will be unity for a full ship. The parameters d and e for different ship types can be found in Table below. For ships where the cargo is not primarily characterised by mass no functions were obtained. For these cases F should be set to 1. The latter applies to Reefers, Container ships, Ro-Ro ships and Vehicle carriers.
Parameters giving fuel consumption per km as a function of load (adapted from IMO 2nd GHG study).