Getting your rig right

Andy Rice advises a Fireball sailor on the mysteries of prebend and mast rake
Fireball sailor Ralph Gillam wants to know: What is the difference between prebend and mast rake? Prebend and mast rake are two very different things but also very inter-related factors when setting up your rig for optimum speed. Prebend is the amount of bend in your mast after you have pulled on the rig tension. Mast rake is simply the term used to describe the angle that your mast sits fore and aft in the boat with the rig tension on. Measuring prebend To measure prebend, pull on the rig tension to the amount specified by your sailmaker or an acknowledged expert in your class. For the Fireball, 400lbs is a typical setting. The Loos Tension Gauge is considered the benchmark tool for this job, and is available from most chandlers. On a conventional dinghy like a Fireball, make sure there is no tension in the deck-level mast control, whether it be a mast strut or wooden chocks. The purpose of measuring prebend is to measure the amount of bend the spreaders are applying to the mast, without other factors coming into play. Next, take the mainsail halyard and tie it off tightly to the gooseneck fitting on the aft face of the mast. The halyard needs to be taught for accurate measurement, but not so taught that it affects the bend of the mast. Now roll the boat over on to its side so that you can measure the 'deflection' at spreader level. This means using a tape measure to record the distance between the back of the mast track at spreader level (bottom set of spreaders on a boat like a 14 or RS800) and the tensioned main halyard. For a Fireball dinghy, a typical amount of prebend at spreader level would be between 20-25mm. 2001 world champion Stevie Morrison uses 22mm. When