As well as making oil sketches on panel in 1805, Turner also made a series of sketches on canvas. Sometimes he worked on a boat, painting sketches on a roll of prepared canvas, which he presumably tacked in sections over a frame or board. Each subject was painted to a size approximately 3 by 4 feet (0.9 x 1.2m), which he regularly used for exhibited pictures. This suggests that, potentially, these sketches were the beginnings of pictures which could be refined later in the studio. Some of his exhibited Thames subjects shown after 1805 may even have been begun in this way.