Trim is the bow-to-stern (front-to-back) balance of the dinghy, which affects boat speed. For example, if helm and crew sit towards the stern it will bury (dig in), causing drag (turbulence from the transom) which slows the boat. Helm and crew should adjust their position to reduce drag on each point of sail.
The helm (and crew in a double-handed boat) work together to ensure the sails are working effectively on each point of sail. Both the jib and the mainsail should be trimmed together so they are just ‘not flapping’. Always try to ease the sail to check.
Indicators such as sail tell-tales are used on the jib and mainsail to illustrate airflow. As students become familiar with this concept, they can progress on to using sail tell-tales.