argon as the flushed inert and insulation gas. Argon has a better insulation power than nitrogen, which could save 10% of boil-off gas. CS1 CS1 stands for Combined System Number One. It was designed by the now merged Gaztransport & Technigaz companies and consists of the best components of both MkIII and No96 systems. The primary barrier is made of invar , and secondary from Triplex. The primary and secondary insulation consists of polyurethane foam panels. Three vessels with CS1 technology were built by one shipyard, but established shipyards have decided to maintain production of the MKIII and NO96. Reliquefaction and boil-off In order to facilitate transport, natural gas is cooled down to approximately at atmospheric pressure, at which point the gas condenses to a liquid. The tanks on board an LNG carrier effectively function as giant thermoses to keep the liquid gas cold during storage. No insulation is perfect, however, and so the liquid is constantly boiling during the voyage. According to WGI, on a typical voyage an estimated 0.1–0.25% of the cargo converts to gas each day, depending on the efficiency of the insulation and the roughness of the voyage. In a typical 20-day voyage, anywhere from 2–6% of the total volume of LNG originally loaded may be lost. Normally an LNG tanker is powered by steam turbines with boilers. These boilers are dual fuel and can run on either methane or oil or a combination of both. The gas produced in boil off is traditionally diverted to the boilers and used as a fuel for the vessel. Before this gas is used in the boilers, it must be warmed up to roughly 20 °C by using the gas heaters. The gas is either fed into the boiler by tank pressure or it is increased in pressure by the Low Duty compressors. What fuel the vessel runs on is dependent on many factors which include the length of the voyage, desire to carry a heel for cooldown, price of oil versus price of LNG, and port demands for cleaner exhaust. There are three basic modes available: Minimum boil-off/maximum oil:- In this mode tank pressures are kept high to reduce boil off to a minimum and the majority of energy comes from the fuel oil. This maximises the amount of LNG delivered but does allow tank temps to rise due to lack of evaporation. The high cargo temps can