Whenever any exporter who has forwarded to the board an estimate of intended exports in terms of section 10(c) fails to export the estimated quantity and in consequence of such failure the board is unable to arrange for the occupation of so much of any shipping space contracted for on the faith of such estimate as would have been occupied but for such failure, the board may charge to him the cost of the shipping space so unoccupied or such other charge as may in the opinion of the board be fairly claimed by a shipowner as a result of such failure, and such charge shall be a debt due by such exporter to the board and may be recovered by the board from him.