Some of the crude oils which are shipped as so-called ‘no heat crudes’ can solidify if the voyage becomes protracted. An intended short voyage can unexpectedly increase in duration due to a sudden port strike for example. The minimum temperature at which cargo is to be maintained is usually 10° celsius above its pour point. It is essential to adhere as closely as possible to the charterer’s instructions on when heating should start and the temperature at which the cargo should be maintained and delivered, having regard to the conditions that are likely to be encountered on the voyage. The wing tanks lose most heat because of their position and conversely, it may be possible to maintain a higher temperature in the centre tanks with their larger volumes and smaller exposed surfaces. If more than one grade is loaded and the volumes and segregation arrangements permit, the higher heat cargo should therefore be stowed in the centre tanks. If a heating problem arises in one or more tanks it may be possible to achieve a satisfactory overall temperature by circulating the cargo, but the charterer should be advised beforehand in such circumstances. When discharging in low ambient temperatures it may be necessary to keep the cargo circulating through the deck lines to prevent solidification and a blockage of the lines. On most existing tankers the suction lines pass through the tanks and the cargo in the tanks keeps these lines heated. Where these lines are not located in the tanks, in OBOs for example, it is important to strip the suction lines after loading to ensure that the cargo remaining in them does not solidify on passage. This is particularly important with some very waxy cargoes. Problems with wax vary greatly depending on sea and air temperatures. A cargo which presents no particular problems in say a tropical area may rapidly solidify in the deck lines during a stoppage in discharging in winter conditions.