Treatment of common costs: allocate shared costs reasonably and apportion depreciation by officer based on asset use. Section 115VJ requires that common costs shared between a tonnage tax business and other activities be allocated on a reasonable basis. For assets other than qualifying ships used for both tonnage tax and other business, depreciation must be apportioned between the two activities in a fair proportion to be determined by the Assessing Officer with reference to the asset's use for the tonnage tax business and for other business.