Inland waterway tanker for transportation of liquid product

An inland waterway tanker for transportation of liquid product over inland waterways, e.g. crude oil. The tanker comprises cargo tanks in a double hull configuration. A combustible fuel powered propulsion engine is cooled preferably by a closed cooling water circuit with a pump and a first heat exchanger arranged in a below waterline recessed compartment to exchange heat between the cooling water and outboard water. A cargo tank heating system comprises a closed thermal oil circuit with heat exchanger ducts to heat the liquid product in the cargo tanks. A high-temperature thermal oil heating device has capacity to heat the thermal oil in said circuit to a temperature above 100 °C. The heating system further comprises a thermal oil circuit heat exchanger adapted to exchange heat between the cooling water and the thermal oil in order to allow for heating of the liquid product in the one or more cargo tanks by heat recovered from the cooling water emerging from the propulsion engine. The cooling water circuit comprises a bypass duct and one or more valves to allow for selectively bypassing the cooling water about the cooling water flow path in the thermal oil circuit heat exchange.