Three masted vessel in the English Channel off Dover?

This watercolour depicts a three-masted vessel under full sail in starboard broadside view with white cliffs and additional vessels in the background. It is signed and dated lower right ‘WA Richards / 07’. Although the artist was active in the late nineteenth and early twentieth centuries, the ship appears to be an early nineteenth-century Royal Navy fifth rate of 36-38 guns. ‘St Lawrence’ is inscribed on the verso.