Are marine paintings usually oils or watercolours?

Oil leads by a wide margin, in 372 of 610 titles. Watercolour is second at 152, and it is rising as a share of live stock. Everything else is occasional. Gouache, pastel and charcoal each appear once or twice, and one listing was a blind-stamped lithograph after a watercolour.

Which coastlines turn up most often?

Yorkshire is the most-named stretch, with Whitby in 22 titles and Scarborough in 16, and Runswick Bay, Staithes, Flamborough and Bridlington recurring beneath them. Venice is the most persistent foreign subject, in 13 titles, taking in the lagoon, the Grand Canal, the Doge's Palace and the Salute. Beyond that the odd outlier arrives: Pearl River junks off Hong Kong, a Brazilian harbour, an Arctic expedition ship.

How old are these paintings?

The dealer-supplied dates run from 1750 to 1960, and 339 of the 610 listings carry a clean year. The rest give a century or a reign. "19th Century" is the single largest bucket at 127, with Victorian at 60 and Edwardian at 16, and a number of listings are simply undated. Seventeenth- and eighteenth-century pieces appear only a handful of times.

Do many come signed by the artist?

Signed appears in 44 titles and attributed in 12, so a named or initialled hand is the norm in the upper half of the range. Roughly a quarter of the sample carries no attribution at all beyond a line like "19th Century Marine Oil Painting". Several signatures are given as initials only.

Why are so many sold as pairs?

Pairs are a standing habit of the genre. "Pair" appears in 37 titles, about one listing in sixteen, and they show up repeatedly in the upper half of the range. Some dealers split a pair and list each half on its own, which is why you also see "1 of 2" and "one of a pair offered separately".

Is one dealer or one school behind most of them?

No. On Sellingantiques 112 different dealers have handled marine paintings, one of the widest spreads in any category, and no single stock defines it. National schools sit at similar low levels too: English, French, Dutch and British all appear, none of them dominant. No artist's name reached three separate dealers.