One of the best things about a Hartley TS 16 is that it can be customised to suit the builder or owner. However, this modification must be controlled when boats race against each other. For this purpose an "A" class certificate was drawn up to ensure that all boats competing in races meet set tolerances to minimise boat design advantage and create a one class racing. Another set of tolerance also applies to the sails that can be used in these events. The two documents are listed below;
