A fortified town on a river, with a sailing boat in the distance, at sunset

For the attribution compare the picture, signed and dated 1641, in a Dutch private collection (H.-U. Beck, Künstler um Jan van Goyen, 1991, p.236, no.625, plate XXXVI).
Dr. H.-U. Beck has kindly suggested the attribution, on the basis of a photograph, in a fax dated 15 September 2000.