There are many factors that affect boat speed, even though all the boats are exactly the same. These include the skipper’s ability to ‘read’ changes (shifts) in the wind direction and also to judge from which direction the wind is arriving at the boat (note, often not the same direction as that at the shore). But, more important than these is what we call ‘sail trim’ (see also ‘Sail Shape’ and ‘Using the Leech Tell-tales’ above).
It will be very rare day that you will be able to race more than one or two races on the same sail trim (wind strength is always changing just as much as its direction). One ‘golden rule’ is that if your boat is not going as fast as the boat at the front of the fleet change your sail trim – and keep practising.