Dual use of liquid fuels—(1) Dual use by the propulsion engine. The tax imposed by section 4042(a) applies to all taxable liquid used as a fuel in the propulsion system of the vessel, regardless of whether the engine (or other propulsion system) is used for a purpose other than propulsion of the vessel. For purposes of this section, any engines generating movement of a vessel (including bow thrusters used for steering) are part of the propulsion system. The tax does not apply to fuel consumed in engines which are not used to generate movement of a vessel. When the propulsion engine operates special equipment by means of a power take-off or power transfer, the tax applies to all liquid fuel consumed by that engine. For example, the tax applies to all fuel used in the engine operating an alternator, a generator, or pumps, if that engine is used to generate movement of a vessel.

Common tank. If the liquid fuel consumed by a nonpropulsion engine is drawn from the same tank as fuel consumed by a propulsion engine, a reasonable determination of the quantity of fuel used in such a separate engine will be acceptable for purposes of excluding from taxation a portion of the fuel consumed by the vessel. The determination of the amount of fuel consumed by the nonpropulsion engine may be based primarily on the operating experience of the person using the fuel; however, in order to exclude fuel from taxation under the rule set out in this paragraph (a)(2), the taxpayer must maintain records which will support the allocation used.

Voyages crossing boundaries of the specified waterways. Fuel consumed by a vessel traveling along the specified waterways is taxable only to the extent of fuel consumed for propulsion while on the specified waterways. Generally, the operator may calculate the amount of fuel consumed while on the specified waterways during a particular voyage by mulitplying total fuel consumed in the propulsion engine by a fraction. The numerator of the fraction is the time spent operating on the specified waterways; the denominator is the total time spent operating on the specified and nonspecified waterways during the voyage. This calculation may not be used when it is unreasonable. It may be determined to be unreasonable by:

Better evidence of fuel consumed (e.g., readings from an accurate fuel gauge or records from similar voyages); or

The existence of factors causing a substantial discrepancy between the rate of fuel consumption on the specified and nonspecified waterways.

Records required. (1) All operators of vessels used in commercial waterway transportation must maintain records sufficient to establish to the satisfaction of the district director the amount of fuel used for taxable purposes. Those records may include, when relevant to establish liability:

Quantity of fuel and date of acquisition of all liquid fuels acquired for both taxable and nontaxable purposes, whether delivered to storage tanks or tanks on a vessel;

Date and quantity of fuel pumped into tanks on each vessel;

Identification number or name of each vessel using fuel; and

Departure time, departure point, route traveled, destination, and arrival time for each vessel.

Vessel operators seeking a tax exemption provided by section 4042(c) must maintain records which will support any exemption claimed. Where applicable, the records shall contain:

The draft of the vessel on each voyage (for exemption under section 4042(c)(1));

The type of vessel in which fuel is consumed and the type of vessel in which cargo is transported (for exemption under section 4042(c) (1), (2) or (4); and

The ultimate use of cargo transported (for exemption under section 4042(c)(3)).