A lot of studies on the economical benefits of modern LNG carrier propulsion systems have already been published. Their results, however, are usually based on certain assumptions regarding oil and gas prices (HFO, LNG purchasing and selling price). In fact, by an appropriate choice of oil- and gas price combination one can produce almost any result needed – either in favour towards the one or the other propulsion solution. It is not without any reason, therefore, that such kind of studies are acknowledged with reservations and caution by the specialized readers.

To better support its customers in their investment decision, MAN Diesel has developed a method, which permits to compare the profitability of two different LNG propulsion systems “A” and “B” for all possible oil- & gas price combinations in just one chart. A method, which reduces an apparently complex problem to its main parameters of influence and illustrates the basic trends in a simple and accessible way – the charterer nomogram.

This nomogram explained in this paper answers the question under which conditions an LNG carrier propulsion system “A” is more profitable then another LNG carrier propulsion system “B” from the charterers view, who plays a decisive role in the LNG transport chain. It will be shown that the solution to this question can be derived by a purely mathematical consideration.