The Thames A Class Rater is both a historic and modern specialist sailing craft designed for the particular conditions at Thames Sailing Club, on the River Thames at Surbiton in England. The class is a development of the Half Rater, which was designed by Linton Hope in 1907. The rules refer to the craft as a yacht.

The rig is lofty, supported by standing rigging and usually by runners, and the hull is a scow with metal centreplate.

All boats built before 1922 are made from wood whilst those built since are of a different construction.

The rater is extremely fast, planes easily, and is a technically highly challenging boat to sail in anything above moderate wind conditions. It is usually sailed with a crew of three.